The field of molecule magnets has advanced significantly in recent years.Yet,key challenges persist for their practical applications,such as achieving higher blocking temperatures and maintaining precise temperature c...The field of molecule magnets has advanced significantly in recent years.Yet,key challenges persist for their practical applications,such as achieving higher blocking temperatures and maintaining precise temperature control in air-stable magnets.This work addresses aspects related to both challenges.Thus,it presents the air-stable hexagonal bipyramidal compound{[Dy(L^(N6en))(OSiPh_(3))_(2)](BPh_(4))}·1.5CH_(2)Cl_(2)(1·1.5CH_(2)Cl_(2))and its diluted analogue{[Dy_(0.1)Y_(0.9)(L^(N6en))(OSiPh_(3))_(2)](BPh_(4))}·1.5CH_(2)Cl_(2)(1@Y·1.5CH_(2)Cl_(2)).Their high axiality,achieved by reducing equatorial charge,enables magnetic behaviour with energy barriers higher than 1500 K and blocking temperatures based on hysteresis(T_(B)^(H))of 12 and 40 K,respectively.Hence,1@Y·1.5CH_(2)Cl_(2) is the SMM with the highest T_(B)^(H) reported among air-stable uncapsulated molecule magnets.Besides,both complexes show temperature-dependent luminescence.Remarkably,1@Y·1.5CH_(2)Cl_(2) stands out as the pioneering example of a bifunctional molecule magnet and luminescent thermometer with both functionalities active below its T_(B)^(H).This breakthrough makes it possible to monitor the temperature of a molecule in the range where it exhibits remanent magnetization for the first time.Moreover,this molecular material presents by far the best magnetic characteristics(U_(eff) and T_(B)^(H))of any SMM luminescent thermometer reported to date.Experimental magnetic and luminescent data are analysed using theoretical calculations.Notably,luminescence is interpreted via coupled cluster methods,offering a more sophisticated alternative to the traditional time-dependent DFT approach.展开更多
A tetranuclear heterometallic butterfly-shaped complex of molecular formula;[Cr^(Ⅲ)_(2)Dy^(Ⅲ)_(2)(OMe)_(2)(mdea)_(2)(benz)_(4)(NO_(3))_(2)](mdeaH_(2)=N-methyldiethanolamine,benz=benzoate)was reported by us and found...A tetranuclear heterometallic butterfly-shaped complex of molecular formula;[Cr^(Ⅲ)_(2)Dy^(Ⅲ)_(2)(OMe)_(2)(mdea)_(2)(benz)_(4)(NO_(3))_(2)](mdeaH_(2)=N-methyldiethanolamine,benz=benzoate)was reported by us and found to display single-molecule magnetism(SMM)behaviour with a Ueff=54 cm^(−1)and well-resolved magnetisation hysteresis plots,with a blocking temperature,T_(B)=3.5 K.In the present study,fourteen related{Cr^(Ⅲ)2 Dy^(Ⅲ)_(2)}complexes have been synthesised,and their magnetic properties have been studied.The study probes how chemical changes in bridging ligands and coordination environment affect the SMM properties compared to the parent complex.We show that by making simple chemical modifications to the ligands,the Ueff and T_(B)values change,with Ueff values ranging from 22 to 65 cm^(−1)and T_(B)1.8 K to 4.7 K.We also show that SMM behaviour can be turned off by manipulation of the coordination sphere around the Dy^(Ⅲ)ion.Based on these experimental results,we undertook a detailed theoretical study to understand why these changes occur.The theoretical studies further describe the mode of exchange mechanism in such complexes and how it controls the blocking temperature.Further,we have found that the exchange coupling between the Dy^(Ⅲ)–Cr^(Ⅲ)ions strongly influences the magnetic relaxation for this family of complexes,and interestingly,the exchange between the Cr^(Ⅲ)–Cr^(Ⅲ)centres plays a determining role in the overall SMM properties,which has been ignored in previous studies.We have derived a relation between the magnetic exchange and T_(B)for such 3d–4f SMMs where exchange coupled states play a dominant role,revealing the blocking temperature is strongly correlated to the overall magnetic exchange.This clearly illustrates the importance of inducing strong exchange coupling to enhance not only the magnetisation reversal barrier but also T_(B)via quenching of zero-field quantum tunnelling of the magnetisation(QTM)in{3d–4f}type complexes.展开更多
A combination of rich phthalocyanine chemistry such as peripheral substitution and the unique properties of lanthanides to enhance organic radical-f interaction is expected to afford new SIMs with a higher working tem...A combination of rich phthalocyanine chemistry such as peripheral substitution and the unique properties of lanthanides to enhance organic radical-f interaction is expected to afford new SIMs with a higher working temperature.展开更多
We present a general relationship between the magnetisation blocking temperature(T_(B))measured using the zero-field cooling/field cooling technique(ZFC/FC)and the temperature-dependent spin relaxation time obtained f...We present a general relationship between the magnetisation blocking temperature(T_(B))measured using the zero-field cooling/field cooling technique(ZFC/FC)and the temperature-dependent spin relaxation time obtained from AC susceptibility and magnetisation decay measurements.The presented mathematical approach supplies ZFC/FC blocking temperatures at any heating rate(R_(H)),providing comparable values to those obtained experimentally,as demonstrated by testing 107 examples for reported singlemolecule magnets(SMMs)where the ZFC/FC curve has been measured.This procedure is examined in further detail for a new single-molecule magnet,[Dy(OPAd_(2)Bz)_(2)(H_(2)O)4Br]Br_(2)·4THF(1)(OPAd_(2)Bz:di(1-adamantyl)benzylphosphine oxide).For this compound,ZFC/FC measurements were made over a broad range of heating rates(0.01-5 K min^(−1)),which agreed with the general behaviour predicted from AC susceptibility data.We discuss how the demagnetisation mechanism determines the sensitivity of T_(B)with respect to the heating rate:T_(B)is mostly insensitive to R_(H)for Orbach relaxation,while there is a larger sensitivity for Raman-limited systems.Our conclusions provide a clear physical interpretation of ZFC/FC blocking temperatures,aiding in the proper contextualization of this figure of merit.展开更多
Two one-dimensional coordination polymers were synthesized:[M(hfac)_(2)(9-PhentNIT)]_(n),where M=Mn(1)or Co(2),hfac^(-)is hexafluoroacetylacetonato and 9-PhentNIT is a new stable nitronyl nitroxide organic radical,2-(...Two one-dimensional coordination polymers were synthesized:[M(hfac)_(2)(9-PhentNIT)]_(n),where M=Mn(1)or Co(2),hfac^(-)is hexafluoroacetylacetonato and 9-PhentNIT is a new stable nitronyl nitroxide organic radical,2-(9-phenanthrenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide.These two complexes are isomorphous and crystallized with metal ions coordinated by two aminoxyl groups,arising from two bridging 9-PhentNIT radicals and two hfac^(-)chelating ligands.展开更多
This paper examines an asymmetric spatiotemporal connection and climatic impact between the winter atmospheric blocking activity in the Euro-Atlantic sector and the life cycle of the North Atlantic Oscillation（NAO） ...This paper examines an asymmetric spatiotemporal connection and climatic impact between the winter atmospheric blocking activity in the Euro-Atlantic sector and the life cycle of the North Atlantic Oscillation（NAO） during the period 1950–2012. Results show that, for positive NAO（NAO＋） events, the instantaneous blocking（IB） frequency exhibits an enhancement along the southwest–northeast（SW–NE） direction from the eastern Atlantic to northeastern Europe（SW–NE pattern, hereafter）, which is particularly evident during the NAO＋decaying stage. By contrast, for negative NAO（NAO-）events, the IB frequency exhibits a spatially asymmetric southeast–northwest（SE–NW） distribution from central Europe to the North Atlantic and Greenland（SE–NW pattern, hereafter）. Moreover, for NAO-（NAO＋） events, the most marked decrease（increase） in the surface air temperature（SAT） in winter over northern Europe is in the decaying stage. For NAO＋events, the dominant positive temperature and precipitation anomalies exhibit the SW–NE-oriented distribution from western to northeastern Europe, which is parallel to the NAO＋-related blocking frequency distribution. For NAO-events, the dominant negative temperature anomaly is in northern and central Europe, whereas the dominant positive precipitation anomaly is distributed over southern Europe along the SW–NE direction. In addition, the downward infrared radiation controlled by the NAO＇s circulation plays a crucial role in the SAT anomaly distribution. It is further shown that the NAO＇s phase can act as an asymmetric impact on the European climate through producing this asymmetric spatiotemporal connection with the Euro-Atlantic IB frequency.展开更多
Using an effective field theory with correlations, magnetic properties of an octahedral chain described by a mixed spin Ising model are investigated. Unique phenomena such as multiple hysteresis loops, saturation magn...Using an effective field theory with correlations, magnetic properties of an octahedral chain described by a mixed spin Ising model are investigated. Unique phenomena such as multiple hysteresis loops, saturation magnetization, and reverse flip of the magnetization plateaus occur when certain typical parameters are applied. These results may be helpful to further investigate the magnetic properties of one-dimensional systems and could potentially be utilized in the design of spin devices.展开更多
A new single-molecule magnet [Mn11Fe1O12 （CH3COO）16（H2O）4]·2CH3COOH·4H2O （Mn11Fe1） has been synthesized. The structure has been studied by the single crystal x-ray diffraction. The difference of Jahn-T...A new single-molecule magnet [Mn11Fe1O12 （CH3COO）16（H2O）4]·2CH3COOH·4H2O （Mn11Fe1） has been synthesized. The structure has been studied by the single crystal x-ray diffraction. The difference of Jahn-Teller distortion between Fe^3＋ and Mn^3＋ ion reveals that Fe^3＋ ion substitutes for Mn^3＋ ion on the Mn（3） sites in the Mn12 skeleton. The temperature dependence of the magnetization gives a blocking temperature TB=1.9K for Mn11Fe1. Based on the magnetization process analysis of the crystal at T=2K, we suggest that Mn11Fe1 has the ground state with a total spin S=11/2.展开更多
The recent breakthrough of attaining a blocking temperature near liquid N2 temperature rekindled the interest in lanthanide-based single molecule magnets (SMMs) for end-user applications.Within this realm,several chal...The recent breakthrough of attaining a blocking temperature near liquid N2 temperature rekindled the interest in lanthanide-based single molecule magnets (SMMs) for end-user applications.Within this realm,several challenges are present,with a key objective being the further enhancement of the blocking temperature.As the current set of molecules based on Dy^(III) have already reached their maximum potential barrier height for magnetisation reversal (Ueff),chemical insight-based developments are hampered.To address these challenges,using density functional theory (DFT) and ab initio complete active space self-consistent field (CASSCF) methods,we have explored the possibility of obtaining lanthanide SMMs in high-valent oxidation states such as +4 and +5.We begin with various small models of [LnO_(2)]^(+),[LnO_(2)],and [LnO_(2)]- (Ln varying from Ce to Lu) systems to correlate the nature of the lanthanides to the SMM characteristics.We have also extended our study to include eight complexes reported earlier possessing +4 and +5 oxidation states to offer clues to improve the SMM characteristics.Our calculations reveal several advantages in fine-tuning the oxidation states in lanthanide SMMs,including the following: (i) increased lanthanide-ligand covalency compared to the Ln^(III) counterpart,(ii) a magnetisation reversal barrier height as high as 8424 cm-1,an unprecedented value compared to any models reported,(iii) among various ways to stabilise such high-oxidation states,encapsulation yielding several targets,with HoO_(2)@SWCNT(4,4) predicted to yield an impressive energy barrier of ∼5400 cm-1 and (iv) stronger lanthanide-ligand bonds that were also found to quench spin-phonon relaxation,as they offset the vibrations that cause this relaxation.These potentially yield higher blocking temperatures,offering a novel strategy for developing a new class of lanthanide SMMs.展开更多
We report here a new Dy^(Ⅲ)-SIM[Dy(OPCy_(3))_(2)(H_(2)O)_(5)](CF_(3)SO_(3))_(3)·_(2)OPCy_(3)(OPCy_(3)=tricyclohexylphosphine oxide)with a pentagonal bipyramidal geometry,which exhibits a blocking temperature T_(...We report here a new Dy^(Ⅲ)-SIM[Dy(OPCy_(3))_(2)(H_(2)O)_(5)](CF_(3)SO_(3))_(3)·_(2)OPCy_(3)(OPCy_(3)=tricyclohexylphosphine oxide)with a pentagonal bipyramidal geometry,which exhibits a blocking temperature T_(B)=8.5 K and an anisotropy barrier U_(eff)=562 K.Ab initio calculations show that this complex exhibits the largest U_(calc)=732 K among the Dy^(Ⅲ)-SIM complexes containing the[Dy(L)_(2)(H_(2)O)_(5)]^(3+)(L=phosphine oxide derivative)cationic unit.展开更多
Lanthanide-based single-molecule magnets(Ln-SMMs)have become the most conspicuous SMMs exhibiting the highest effective barrier(U_(eff))and blocking temperature(T_(B)).Different strategies have been proposed to constr...Lanthanide-based single-molecule magnets(Ln-SMMs)have become the most conspicuous SMMs exhibiting the highest effective barrier(U_(eff))and blocking temperature(T_(B)).Different strategies have been proposed to construct high-performance SMMs,including reducing the coordination number to generate high-order local symmetry and weakened molecular vibrations,thus reducing the possibility of spin-vibration interaction.However,the synthesis of low-coordinate Ln(III)complexes is still very challenging owing to their large ionic radius and ionic nature,especially when the coordination number is lower than five.Herein,two bis(imidazolin-2-iminato)dysprosium_((III))SMMs[Dy(Im^(Dipp)N)_(2)(Bn)(THF)](1)and[Dy(Im^(Dipp)N)_(2)(BPh_(4))](2)(Im^(Dipp)NH=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-imine,Bn=benzyl)were synthesized and characterized.The four-coordinate complex 1 possessed a U_(eff)of 593 K and a T_(B)of 8 K,while complex 2 exhibited a U_(eff)of 343 K.The weaker equatorial crystal field in 1 than 2 could suppress the quantum tunneling of magnetization(QTM),leading to a higher U_(eff).Moreover,calculations on model structures indicated that constructing bis(imidazolin-2-iminato)single-molecule magnets with a higher U_(eff)and T_(B)is possible by further regulating the electronic effects and steric hindrance of imidazolin-2-iminato ligands.展开更多
In recent years,very significant progress has been made in single-molecule magnets (SMMs),and one of the major milestone works is the hysteresis blocking temperature beyond the boiling point of liquid nitrogen.As incr...In recent years,very significant progress has been made in single-molecule magnets (SMMs),and one of the major milestone works is the hysteresis blocking temperature beyond the boiling point of liquid nitrogen.As increasingly abundant experimental and theoretical cases are studied,our understanding of how to construct high-performance rare-earth SMMs is becoming clearer,while few good SMMs have been reported for actinides that possess stronger spin-orbital coupling than rare earths.Recently,attempts to replicate the successful strategy on rare-earth SMMs to actinides have proven to be a failure,or at least frustrating,with the main reason being the stronger covalent contribution in the actinide-ligand bonds.In this review,the progress on actinide SMMs is summarized to look back at how far we have come and try to find possible routes forward.展开更多
Cold air outbreaks（CAOs）always hit East Asia during boreal winter and have significant impacts on human health and public transport.The amplitude and route of CAOs are closely associated with blocking circulations o...Cold air outbreaks（CAOs）always hit East Asia during boreal winter and have significant impacts on human health and public transport.The amplitude and route of CAOs are closely associated with blocking circulations over the Eurasian continent.Two categories of CAOs are recognized,namely,the ordinary cold wave events（CWEs）and the extensive and persistent extreme cold events（EPECEs）,with the latter having even stronger impacts.The blocking features associated with these two types of CAOs and their differences are investigated in this study on the intraseasonal timescale.What these two CAOs do have in common is that they are both preceded by the intensification and recurrence of a blocking high over the midlatitude North Atlantic.The difference between these events is primarily reflected on the spatial scale and duration of the corresponding blocking high.During the CWEs,blocking occurs around the Ural Mountains,and exhibits a regional feature.The resulting cold air temperature persists for only up to 8 days.In contrast,during the EPECEs,the blocking region is quite extensive and is not only confined around the Ural Mountains but also extends eastward into Northeast Asia in a southwest–northeast orientation.As a result,the cold air tends to accumulate over a large area and persists for a much longer time.The blocking activity is primarily induced by an increased frequency and eastward extension of the synoptic anticyclonic Rossby wave breaking（AWB）.Compared with the CWEs,characterized by a regional and short-lived synoptic AWB frequency,the EPE-CEs tend to be accompanied by more recurrent and eastward extensions of the synoptic AWB.展开更多
An orthogonal coupling structure of NiO/CoPt/Pt/glass with perpendicular exchange bias effect has been prepared.The exchange bias is found to be strongly dependent on the interface roughness between NiO and CoPt layer...An orthogonal coupling structure of NiO/CoPt/Pt/glass with perpendicular exchange bias effect has been prepared.The exchange bias is found to be strongly dependent on the interface roughness between NiO and CoPt layer.The conventional inverse proportionality of the exchange bias field with the ferromagnetic thickness is not applicable to this top-pinned stacking structure.Moreover,an anomalous ferromagnetic thickness dependence of blocking temperature is also observed.A simulation on the basis of a spin configuration model with defects at the interface agrees well with the experimental observations.These findings suggest considerable contribution of the interface roughness to the perpendicular exchange bias.展开更多
Many sandwich-type lanthanide complexes show extremely high energy barriers(Ueff)for the reversal of magnetization and high blocking temperatures,being the star molecules in the research area of single-molecule magnet...Many sandwich-type lanthanide complexes show extremely high energy barriers(Ueff)for the reversal of magnetization and high blocking temperatures,being the star molecules in the research area of single-molecule magnets.Herein,the preparation,structural determination,and magnetic property studies of two ansa-bridged Er-COT(COT=cyclooctatetraenyl dianion)complexes[KDME_(2)][Er((η^(8)-COT-Si^(Me2))_(2)O)](1)and[KDME_(2)][Er((η^(8)-COT-Si^(iPr2))_(2)O)]K[Er((η^(8)-COT-Si^(iPr2))_(2)O)](2)were reported.The Er(Ⅲ)ions in both complexes are sandwiched by two COT rings which are ansa-bridged by a[Si-O-Si]group.Magnetic studies reveal both complexes display slow magnetic relaxations with comparable energy barriers(228(5)K for 1,and 196(4)K for 2)and blocking temperatures(10.5 K for both complexes).The difference in the relaxation times(τ)for the two complexes was studied in details:different molecular vibrations induced by the substituents are the main reason forτfor 1 being about 10 times longer than for 2 at the same temperature above 10 K,while the quantum tunnelling of magnetization relaxation time(τQTM)for 2 is about 10 times longer than for 1 below 8 K,probably owing to the different dipolar interactions.Further rearrangement of molecular network with such ansa-bridged SMMs is promising to design molecular magnetic materials with enhanced properties or new properties.展开更多
基金supported by Universidade de Santiago de Compostela(2024-PU027-1)Consellería de Cultura,Educación,Formación Profesional e Universidades,Xunta de Galicia(convenio 2023-1298)+3 种基金by Portuguese funds through the FCT/MCTES(PIDDAC)(UIDB/50011/2020,https://doi.org/10.54499/UIDB/50011/2020,UIDP/50011/2020,https://doi.org/10.54499/UIDP/50011/2020,and LA/P/0006/2020,https://doi.org/10.54499/LA/P/0006/2020 projects of the CICECO-Aveiro Institute of Materials)by Ministerio de Ciencia,Innovación y Universidades(PID2021-122464NB-I00 and Maria de Maeztu CEX2021-001202-M).COST Action CA22131,supported by COST(European Cooperation in Science and Technology)Xunta de Galicia for his postdoctoral fellowship(ED481B-2022-068).the Generalitat de Catalunya for the 2021-SGR-00286 grantE.R.for an ICREA Academia grant.
文摘The field of molecule magnets has advanced significantly in recent years.Yet,key challenges persist for their practical applications,such as achieving higher blocking temperatures and maintaining precise temperature control in air-stable magnets.This work addresses aspects related to both challenges.Thus,it presents the air-stable hexagonal bipyramidal compound{[Dy(L^(N6en))(OSiPh_(3))_(2)](BPh_(4))}·1.5CH_(2)Cl_(2)(1·1.5CH_(2)Cl_(2))and its diluted analogue{[Dy_(0.1)Y_(0.9)(L^(N6en))(OSiPh_(3))_(2)](BPh_(4))}·1.5CH_(2)Cl_(2)(1@Y·1.5CH_(2)Cl_(2)).Their high axiality,achieved by reducing equatorial charge,enables magnetic behaviour with energy barriers higher than 1500 K and blocking temperatures based on hysteresis(T_(B)^(H))of 12 and 40 K,respectively.Hence,1@Y·1.5CH_(2)Cl_(2) is the SMM with the highest T_(B)^(H) reported among air-stable uncapsulated molecule magnets.Besides,both complexes show temperature-dependent luminescence.Remarkably,1@Y·1.5CH_(2)Cl_(2) stands out as the pioneering example of a bifunctional molecule magnet and luminescent thermometer with both functionalities active below its T_(B)^(H).This breakthrough makes it possible to monitor the temperature of a molecule in the range where it exhibits remanent magnetization for the first time.Moreover,this molecular material presents by far the best magnetic characteristics(U_(eff) and T_(B)^(H))of any SMM luminescent thermometer reported to date.Experimental magnetic and luminescent data are analysed using theoretical calculations.Notably,luminescence is interpreted via coupled cluster methods,offering a more sophisticated alternative to the traditional time-dependent DFT approach.
基金We thank DST and SERB(SB/SJF/2019-20/12,CRG/2022/001697)for fundingAS thanks UGC/CSIR for the fellowship+1 种基金the financial support from the Prime Ministers Research Fellowship(PMRF)the Australian Research Council(DP110100525)for a Discovery grant.
文摘A tetranuclear heterometallic butterfly-shaped complex of molecular formula;[Cr^(Ⅲ)_(2)Dy^(Ⅲ)_(2)(OMe)_(2)(mdea)_(2)(benz)_(4)(NO_(3))_(2)](mdeaH_(2)=N-methyldiethanolamine,benz=benzoate)was reported by us and found to display single-molecule magnetism(SMM)behaviour with a Ueff=54 cm^(−1)and well-resolved magnetisation hysteresis plots,with a blocking temperature,T_(B)=3.5 K.In the present study,fourteen related{Cr^(Ⅲ)2 Dy^(Ⅲ)_(2)}complexes have been synthesised,and their magnetic properties have been studied.The study probes how chemical changes in bridging ligands and coordination environment affect the SMM properties compared to the parent complex.We show that by making simple chemical modifications to the ligands,the Ueff and T_(B)values change,with Ueff values ranging from 22 to 65 cm^(−1)and T_(B)1.8 K to 4.7 K.We also show that SMM behaviour can be turned off by manipulation of the coordination sphere around the Dy^(Ⅲ)ion.Based on these experimental results,we undertook a detailed theoretical study to understand why these changes occur.The theoretical studies further describe the mode of exchange mechanism in such complexes and how it controls the blocking temperature.Further,we have found that the exchange coupling between the Dy^(Ⅲ)–Cr^(Ⅲ)ions strongly influences the magnetic relaxation for this family of complexes,and interestingly,the exchange between the Cr^(Ⅲ)–Cr^(Ⅲ)centres plays a determining role in the overall SMM properties,which has been ignored in previous studies.We have derived a relation between the magnetic exchange and T_(B)for such 3d–4f SMMs where exchange coupled states play a dominant role,revealing the blocking temperature is strongly correlated to the overall magnetic exchange.This clearly illustrates the importance of inducing strong exchange coupling to enhance not only the magnetisation reversal barrier but also T_(B)via quenching of zero-field quantum tunnelling of the magnetisation(QTM)in{3d–4f}type complexes.
文摘A combination of rich phthalocyanine chemistry such as peripheral substitution and the unique properties of lanthanides to enhance organic radical-f interaction is expected to afford new SIMs with a higher working temperature.
基金FONDECYT Regular 1210325 for financial support.Powered@NLHPC:this research was partially supported by the supercomputing infrastructure of the NLHPC(ECM-02)Financial support from the Ministerio de Ciencia e Innovación(projects PID2022-138090NB-C21,PID2021-122464NB-I00,TED2021-129593B-I00,CNS2023-144561 and Maria de Maeztu CEX2021-001202-M)+5 种基金the Junta de Andalucía(FQM-195 and FQM-337)FEDER/Junta de Andalucía(projects I+D+i P20_00692,C-EXP-140-UGR23 and M.1.B.B TA_000722,Programas Operativos FEDER 2014-2020 y 2021-2027,Consejería de Economía,Conocimiento,Empresas y Universidad)the University of Granada(project I+D+i PPJIA2020.10)is greatly appreciatedthe Centro de Servicios de Informática y Redes de Comunicaciones(CSIRC)for computational time and facilitiesthe Ministerio de Ciencia e Innovación for a Ramón y Cajal contract(the publication is part of the project PID2022-138090NB-C21 and grant RYC2021-034288-I funded by MCIN/AEI/10.13039/501100011033 and by the European Union“NextGenerationEU”/PRTR”)the Generalitat de Catalunya for ICREA Academia and 2021-SGR-00286 grants,and for computational resources at CSUC.
文摘We present a general relationship between the magnetisation blocking temperature(T_(B))measured using the zero-field cooling/field cooling technique(ZFC/FC)and the temperature-dependent spin relaxation time obtained from AC susceptibility and magnetisation decay measurements.The presented mathematical approach supplies ZFC/FC blocking temperatures at any heating rate(R_(H)),providing comparable values to those obtained experimentally,as demonstrated by testing 107 examples for reported singlemolecule magnets(SMMs)where the ZFC/FC curve has been measured.This procedure is examined in further detail for a new single-molecule magnet,[Dy(OPAd_(2)Bz)_(2)(H_(2)O)4Br]Br_(2)·4THF(1)(OPAd_(2)Bz:di(1-adamantyl)benzylphosphine oxide).For this compound,ZFC/FC measurements were made over a broad range of heating rates(0.01-5 K min^(−1)),which agreed with the general behaviour predicted from AC susceptibility data.We discuss how the demagnetisation mechanism determines the sensitivity of T_(B)with respect to the heating rate:T_(B)is mostly insensitive to R_(H)for Orbach relaxation,while there is a larger sensitivity for Raman-limited systems.Our conclusions provide a clear physical interpretation of ZFC/FC blocking temperatures,aiding in the proper contextualization of this figure of merit.
基金CAPES-PrInt-Universidade Federal Fluminense-988887.310269/2018-00.T.A.C.thanks CAPES for the fellowshipThe authors thank FAPERJ and CNPq(Brazil),ICUB(University of Bucharest)and UEFISCDI(Romania)for financial support.This research used facilities of the Brazilian Synchrotron Light Laboratory(LNLS)The MANACÁbeamline(projects 20231062 and 20233038)as well as staff member Dr Andrey F.Z.Nascimento are acknowledged.
文摘Two one-dimensional coordination polymers were synthesized:[M(hfac)_(2)(9-PhentNIT)]_(n),where M=Mn(1)or Co(2),hfac^(-)is hexafluoroacetylacetonato and 9-PhentNIT is a new stable nitronyl nitroxide organic radical,2-(9-phenanthrenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide.These two complexes are isomorphous and crystallized with metal ions coordinated by two aminoxyl groups,arising from two bridging 9-PhentNIT radicals and two hfac^(-)chelating ligands.
基金support from the National Natural Science Foundation of China (Grant Nos. 41505075 and 41790473)the National Key Research and Development Program of China (Grant No. 2016YFA0601802)
文摘This paper examines an asymmetric spatiotemporal connection and climatic impact between the winter atmospheric blocking activity in the Euro-Atlantic sector and the life cycle of the North Atlantic Oscillation（NAO） during the period 1950–2012. Results show that, for positive NAO（NAO＋） events, the instantaneous blocking（IB） frequency exhibits an enhancement along the southwest–northeast（SW–NE） direction from the eastern Atlantic to northeastern Europe（SW–NE pattern, hereafter）, which is particularly evident during the NAO＋decaying stage. By contrast, for negative NAO（NAO-）events, the IB frequency exhibits a spatially asymmetric southeast–northwest（SE–NW） distribution from central Europe to the North Atlantic and Greenland（SE–NW pattern, hereafter）. Moreover, for NAO-（NAO＋） events, the most marked decrease（increase） in the surface air temperature（SAT） in winter over northern Europe is in the decaying stage. For NAO＋events, the dominant positive temperature and precipitation anomalies exhibit the SW–NE-oriented distribution from western to northeastern Europe, which is parallel to the NAO＋-related blocking frequency distribution. For NAO-events, the dominant negative temperature anomaly is in northern and central Europe, whereas the dominant positive precipitation anomaly is distributed over southern Europe along the SW–NE direction. In addition, the downward infrared radiation controlled by the NAO＇s circulation plays a crucial role in the SAT anomaly distribution. It is further shown that the NAO＇s phase can act as an asymmetric impact on the European climate through producing this asymmetric spatiotemporal connection with the Euro-Atlantic IB frequency.
基金Project supported by National Natural Science Foundation of China(Grant No.51920105011)the Key R&D Program of Liaoning Province of China(Grant No.2020JH2/10300079)。
文摘Using an effective field theory with correlations, magnetic properties of an octahedral chain described by a mixed spin Ising model are investigated. Unique phenomena such as multiple hysteresis loops, saturation magnetization, and reverse flip of the magnetization plateaus occur when certain typical parameters are applied. These results may be helpful to further investigate the magnetic properties of one-dimensional systems and could potentially be utilized in the design of spin devices.
基金Project supported by the National Natural Science Foundation of China （Grant No 10375088）.
文摘A new single-molecule magnet [Mn11Fe1O12 （CH3COO）16（H2O）4]·2CH3COOH·4H2O （Mn11Fe1） has been synthesized. The structure has been studied by the single crystal x-ray diffraction. The difference of Jahn-Teller distortion between Fe^3＋ and Mn^3＋ ion reveals that Fe^3＋ ion substitutes for Mn^3＋ ion on the Mn（3） sites in the Mn12 skeleton. The temperature dependence of the magnetization gives a blocking temperature TB=1.9K for Mn11Fe1. Based on the magnetization process analysis of the crystal at T=2K, we suggest that Mn11Fe1 has the ground state with a total spin S=11/2.
基金A.S.is thankful to IITB for the IPDF.G.R.would like to thank SERB(SB/SJF/2019-20/12,CRG/2022/001697)for funding.
文摘The recent breakthrough of attaining a blocking temperature near liquid N2 temperature rekindled the interest in lanthanide-based single molecule magnets (SMMs) for end-user applications.Within this realm,several challenges are present,with a key objective being the further enhancement of the blocking temperature.As the current set of molecules based on Dy^(III) have already reached their maximum potential barrier height for magnetisation reversal (Ueff),chemical insight-based developments are hampered.To address these challenges,using density functional theory (DFT) and ab initio complete active space self-consistent field (CASSCF) methods,we have explored the possibility of obtaining lanthanide SMMs in high-valent oxidation states such as +4 and +5.We begin with various small models of [LnO_(2)]^(+),[LnO_(2)],and [LnO_(2)]- (Ln varying from Ce to Lu) systems to correlate the nature of the lanthanides to the SMM characteristics.We have also extended our study to include eight complexes reported earlier possessing +4 and +5 oxidation states to offer clues to improve the SMM characteristics.Our calculations reveal several advantages in fine-tuning the oxidation states in lanthanide SMMs,including the following: (i) increased lanthanide-ligand covalency compared to the Ln^(III) counterpart,(ii) a magnetisation reversal barrier height as high as 8424 cm-1,an unprecedented value compared to any models reported,(iii) among various ways to stabilise such high-oxidation states,encapsulation yielding several targets,with HoO_(2)@SWCNT(4,4) predicted to yield an impressive energy barrier of ∼5400 cm-1 and (iv) stronger lanthanide-ligand bonds that were also found to quench spin-phonon relaxation,as they offset the vibrations that cause this relaxation.These potentially yield higher blocking temperatures,offering a novel strategy for developing a new class of lanthanide SMMs.
基金support from Ministerio de Economía y Competitividad(MINECO)for Projects CTQ2014-56312-P and PGC2018-102052-B-C21,the Junta de Andalucía(FQM-195)FEDER project A-FQM-172-UGR18 and the University of Granada is gratefully acknowledged+1 种基金A part of this work was carried out at HFLSM,IMR,Tohoku UniversityI.F.D.O.also acknowledges support by COLABS.GR would like to thank the SERB(CRG/2018/000430)for financial support.S.D.thanks the UGC for a Senior Research Fellowship.
文摘We report here a new Dy^(Ⅲ)-SIM[Dy(OPCy_(3))_(2)(H_(2)O)_(5)](CF_(3)SO_(3))_(3)·_(2)OPCy_(3)(OPCy_(3)=tricyclohexylphosphine oxide)with a pentagonal bipyramidal geometry,which exhibits a blocking temperature T_(B)=8.5 K and an anisotropy barrier U_(eff)=562 K.Ab initio calculations show that this complex exhibits the largest U_(calc)=732 K among the Dy^(Ⅲ)-SIM complexes containing the[Dy(L)_(2)(H_(2)O)_(5)]^(3+)(L=phosphine oxide derivative)cationic unit.
基金supported by the NSFC(21971006 and 22131003)the National Basic Research Program of China(2018YFA0306003).
文摘Lanthanide-based single-molecule magnets(Ln-SMMs)have become the most conspicuous SMMs exhibiting the highest effective barrier(U_(eff))and blocking temperature(T_(B)).Different strategies have been proposed to construct high-performance SMMs,including reducing the coordination number to generate high-order local symmetry and weakened molecular vibrations,thus reducing the possibility of spin-vibration interaction.However,the synthesis of low-coordinate Ln(III)complexes is still very challenging owing to their large ionic radius and ionic nature,especially when the coordination number is lower than five.Herein,two bis(imidazolin-2-iminato)dysprosium_((III))SMMs[Dy(Im^(Dipp)N)_(2)(Bn)(THF)](1)and[Dy(Im^(Dipp)N)_(2)(BPh_(4))](2)(Im^(Dipp)NH=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-imine,Bn=benzyl)were synthesized and characterized.The four-coordinate complex 1 possessed a U_(eff)of 593 K and a T_(B)of 8 K,while complex 2 exhibited a U_(eff)of 343 K.The weaker equatorial crystal field in 1 than 2 could suppress the quantum tunneling of magnetization(QTM),leading to a higher U_(eff).Moreover,calculations on model structures indicated that constructing bis(imidazolin-2-iminato)single-molecule magnets with a higher U_(eff)and T_(B)is possible by further regulating the electronic effects and steric hindrance of imidazolin-2-iminato ligands.
基金the National Natural Science Foundation of China(grant no.22131011 and 21821003)the Pearl River Talent Plan of Guangdong(2017BT01C161).
文摘In recent years,very significant progress has been made in single-molecule magnets (SMMs),and one of the major milestone works is the hysteresis blocking temperature beyond the boiling point of liquid nitrogen.As increasingly abundant experimental and theoretical cases are studied,our understanding of how to construct high-performance rare-earth SMMs is becoming clearer,while few good SMMs have been reported for actinides that possess stronger spin-orbital coupling than rare earths.Recently,attempts to replicate the successful strategy on rare-earth SMMs to actinides have proven to be a failure,or at least frustrating,with the main reason being the stronger covalent contribution in the actinide-ligand bonds.In this review,the progress on actinide SMMs is summarized to look back at how far we have come and try to find possible routes forward.
基金Supported by the National Natural Science Foundation of China(41305047,41375064,and 41630424)National Science and Technology Support Program of China(2015BAC03B03)
文摘Cold air outbreaks（CAOs）always hit East Asia during boreal winter and have significant impacts on human health and public transport.The amplitude and route of CAOs are closely associated with blocking circulations over the Eurasian continent.Two categories of CAOs are recognized,namely,the ordinary cold wave events（CWEs）and the extensive and persistent extreme cold events（EPECEs）,with the latter having even stronger impacts.The blocking features associated with these two types of CAOs and their differences are investigated in this study on the intraseasonal timescale.What these two CAOs do have in common is that they are both preceded by the intensification and recurrence of a blocking high over the midlatitude North Atlantic.The difference between these events is primarily reflected on the spatial scale and duration of the corresponding blocking high.During the CWEs,blocking occurs around the Ural Mountains,and exhibits a regional feature.The resulting cold air temperature persists for only up to 8 days.In contrast,during the EPECEs,the blocking region is quite extensive and is not only confined around the Ural Mountains but also extends eastward into Northeast Asia in a southwest–northeast orientation.As a result,the cold air tends to accumulate over a large area and persists for a much longer time.The blocking activity is primarily induced by an increased frequency and eastward extension of the synoptic anticyclonic Rossby wave breaking（AWB）.Compared with the CWEs,characterized by a regional and short-lived synoptic AWB frequency,the EPE-CEs tend to be accompanied by more recurrent and eastward extensions of the synoptic AWB.
文摘An orthogonal coupling structure of NiO/CoPt/Pt/glass with perpendicular exchange bias effect has been prepared.The exchange bias is found to be strongly dependent on the interface roughness between NiO and CoPt layer.The conventional inverse proportionality of the exchange bias field with the ferromagnetic thickness is not applicable to this top-pinned stacking structure.Moreover,an anomalous ferromagnetic thickness dependence of blocking temperature is also observed.A simulation on the basis of a spin configuration model with defects at the interface agrees well with the experimental observations.These findings suggest considerable contribution of the interface roughness to the perpendicular exchange bias.
基金supported by the National Natural Science Foundation of China(92261203,22101116,and 21971106)Key Laboratory of Rare Earth Chemistry of Guangdong Higher Education Institutes(2022KSYS006)+1 种基金the Stable Support Plan Program of Shenzhen Natural Science Fund(20200925161141006)Shenzhen Fundamental Research Program(JCYJ20220530115001002 and JCYJ20220818100417037).
文摘Many sandwich-type lanthanide complexes show extremely high energy barriers(Ueff)for the reversal of magnetization and high blocking temperatures,being the star molecules in the research area of single-molecule magnets.Herein,the preparation,structural determination,and magnetic property studies of two ansa-bridged Er-COT(COT=cyclooctatetraenyl dianion)complexes[KDME_(2)][Er((η^(8)-COT-Si^(Me2))_(2)O)](1)and[KDME_(2)][Er((η^(8)-COT-Si^(iPr2))_(2)O)]K[Er((η^(8)-COT-Si^(iPr2))_(2)O)](2)were reported.The Er(Ⅲ)ions in both complexes are sandwiched by two COT rings which are ansa-bridged by a[Si-O-Si]group.Magnetic studies reveal both complexes display slow magnetic relaxations with comparable energy barriers(228(5)K for 1,and 196(4)K for 2)and blocking temperatures(10.5 K for both complexes).The difference in the relaxation times(τ)for the two complexes was studied in details:different molecular vibrations induced by the substituents are the main reason forτfor 1 being about 10 times longer than for 2 at the same temperature above 10 K,while the quantum tunnelling of magnetization relaxation time(τQTM)for 2 is about 10 times longer than for 1 below 8 K,probably owing to the different dipolar interactions.Further rearrangement of molecular network with such ansa-bridged SMMs is promising to design molecular magnetic materials with enhanced properties or new properties.
