Endohedral clusters inside metallofullerenes experience considerable inner strain when the size of the hosting cage is comparably small.This strain can be tuned in mixed-metal metallofullerenes by combining metals of ...Endohedral clusters inside metallofullerenes experience considerable inner strain when the size of the hosting cage is comparably small.This strain can be tuned in mixed-metal metallofullerenes by combining metals of different sizes.Here we demonstrate that the internal strain and mass can be used as variables to control D_(y)…D_(y)coupling and relaxation of magnetization in D_(y)-metallofullerenes.Mixed-metal nitride clusterfullerenes D_(y)_(x)Y_(3-x)N@Ih-C_(80)(x=0-3)and D_(y)_(2)LaN@Ih-C_(80)combining D_(y)with diamagnetic rare-earth elements,Y and La,were synthesized and characterized by single-crystal X-ray diffraction,SQUID magnetometry,ab initio calculations,and spectroscopic techniques.D_(y)_(x)Y_(3-x)N clusters showed a planar structure,but the slightly larger size of D_(y)^(3+)in comparison with that of Y^(3+)resulted in increased elongation of the nitrogen thermal ellipsoid,showing enhancement of the out-of-plane vibrational amplitude.When D_(y)was combined with larger La,the D_(y)_(2)LaN cluster appeared strongly pyramidal with the distance between two nitrogen sites of 1.15(1)A,whereas D_(y)La_(2)N@C_(80)could not be obtained in a separable yield.Magnetic studies revealed that the relaxation of magnetization and blocking temperature of magnetization in the D_(y)M_(2)N@C_(80)series(M=Sc,Y,Lu)correlated with the mass of M,with D_(y)Sc_(2)N@C_(80)showing the fastest and D_(y)Lu_(2)N@C_(80)the slowest relaxation.Ab initio calculations predicted very similar g-tensors for D_(y)^(3+)ground state pseudospin in all studied D_(y)M_(2)N@C_(80)molecules,suggesting that the variation in relaxation is caused by different vibrational spectra of these compounds.In the D_(y)_(2)MN@C_(80)series(M=Sc,Y,La,Lu),the magnetic and hysteretic behavior was found to correlate with D_(y)…D_(y)coupling,which in turn appears to depend on the size of M^(3+).Across the D_(y)_(2)MN@C_(80)series,the energy difference between ferromagnetic and antiferromagnetic states changes from 5.6 cm^(-1)in D_(y)_(2)ScN@C_(80)to 3.0 cm^(-1)in D_(y)_(2)LuN@C_(80),1.0 cm^(-1)in D_(y)_(2)YN@C_(80),and-0.8 cm^(-1)in D_(y)_(2)LaN@C_(80).The coupling of D_(y)ions suppresses the zero-field quantum tunnelling of magnetization but opens new relaxation channels,making the relaxation rate dependent on the coupling strengths.D_(y)Y_(2)N@C_(80)and D_(y)_(2)YN@C_(80)were found to be non-luminescent,while the luminescence reported for D_(y)Y_(2)N@C_(80)was caused by traces of Y3N@C_(80)and Y_(2)ScN@C_(80).展开更多
The detailed electronic structure of single atomic magnets is a crucial bit in the further understanding and design of a new generation of monoatomic magnetic elements on surfaces and in molecules.Control and manipula...The detailed electronic structure of single atomic magnets is a crucial bit in the further understanding and design of a new generation of monoatomic magnetic elements on surfaces and in molecules.Control and manipulation of the single atomic state,as well as long relaxation of magnetization,have been demonstrated for lanthanide atoms on carefully chosen supporting substrates.However,these convincing experiments are puzzling by insufficient theoretical description,usually omitting the valence electrons of lanthanide atoms.In this work,starting with an idea of the inevitable need of local d-and p-shell electrons for a proper description of the magnetic states of lanthanide atoms,we rationalized the electronic structure and magnetic properties of Ho atom on the MgO substrate using ab initio multiconfigurational approaches.By doing so,we obtained the solution which complements experimental observations and has been able to pin-point the atomic state which most likely to be responsible for the exceptional magnetic properties of Ho on MgO.This study demonstrates that new paradigms are needed for understanding and interpretation of the lanthanide single-atomic magnets.展开更多
Two isomers of metallofullerene Dy_(2)S@C_(82)with sulfur-bridged Dy ions exhibit broad magnetic hysteresis with sharp steps at sub-Kelvin temperature.Analysis of the level crossing events for different orientations o...Two isomers of metallofullerene Dy_(2)S@C_(82)with sulfur-bridged Dy ions exhibit broad magnetic hysteresis with sharp steps at sub-Kelvin temperature.Analysis of the level crossing events for different orientations of a magnetic field showed that even in powder samples,the hysteresis steps caused by quantum tunneling of magnetization can provide precise information on the strength of intramolecular Dy…Dy interactions.A comparison of different methods to determine the energy difference between ferromagnetic and antiferromagnetic states showed that sub-Kelvin hysteresis gives the most robust and reliable values.The ground state in Dy_(2)S@C_(82)has ferromagnetic coupling of Dy magnetic moments,whereas the state with antiferromagnetic coupling in C_(s)and C_(3)v cage isomers is 10.7 and 5.1 cm^(-1)higher,respectively.The value for the C_(s)isomer is among the highest found in metallofullerenes and is considerably larger than that reported in non-fullerene dinuclear molecular magnets.Magnetization relaxation times measured in zero magnetic field at sub-Kelvin temperatures tend to level off near 900 and 3200 s in C_(s)and C_(3)v isomers.These times correspond to the quantum tunneling relaxation mechanism,in which the whole magnetic moment of the Dy_(2)S@C_(82)molecule flips at once as a single entity.展开更多
基金support by Deutsche Forschungsgemeinschaft(grants LI 3055/3-1,PO 1602/6-1,PO 1602/7-1,and AV 169/3-1)the China Scholarship Council(Fellowship to Y.H.).
文摘Endohedral clusters inside metallofullerenes experience considerable inner strain when the size of the hosting cage is comparably small.This strain can be tuned in mixed-metal metallofullerenes by combining metals of different sizes.Here we demonstrate that the internal strain and mass can be used as variables to control D_(y)…D_(y)coupling and relaxation of magnetization in D_(y)-metallofullerenes.Mixed-metal nitride clusterfullerenes D_(y)_(x)Y_(3-x)N@Ih-C_(80)(x=0-3)and D_(y)_(2)LaN@Ih-C_(80)combining D_(y)with diamagnetic rare-earth elements,Y and La,were synthesized and characterized by single-crystal X-ray diffraction,SQUID magnetometry,ab initio calculations,and spectroscopic techniques.D_(y)_(x)Y_(3-x)N clusters showed a planar structure,but the slightly larger size of D_(y)^(3+)in comparison with that of Y^(3+)resulted in increased elongation of the nitrogen thermal ellipsoid,showing enhancement of the out-of-plane vibrational amplitude.When D_(y)was combined with larger La,the D_(y)_(2)LaN cluster appeared strongly pyramidal with the distance between two nitrogen sites of 1.15(1)A,whereas D_(y)La_(2)N@C_(80)could not be obtained in a separable yield.Magnetic studies revealed that the relaxation of magnetization and blocking temperature of magnetization in the D_(y)M_(2)N@C_(80)series(M=Sc,Y,Lu)correlated with the mass of M,with D_(y)Sc_(2)N@C_(80)showing the fastest and D_(y)Lu_(2)N@C_(80)the slowest relaxation.Ab initio calculations predicted very similar g-tensors for D_(y)^(3+)ground state pseudospin in all studied D_(y)M_(2)N@C_(80)molecules,suggesting that the variation in relaxation is caused by different vibrational spectra of these compounds.In the D_(y)_(2)MN@C_(80)series(M=Sc,Y,La,Lu),the magnetic and hysteretic behavior was found to correlate with D_(y)…D_(y)coupling,which in turn appears to depend on the size of M^(3+).Across the D_(y)_(2)MN@C_(80)series,the energy difference between ferromagnetic and antiferromagnetic states changes from 5.6 cm^(-1)in D_(y)_(2)ScN@C_(80)to 3.0 cm^(-1)in D_(y)_(2)LuN@C_(80),1.0 cm^(-1)in D_(y)_(2)YN@C_(80),and-0.8 cm^(-1)in D_(y)_(2)LaN@C_(80).The coupling of D_(y)ions suppresses the zero-field quantum tunnelling of magnetization but opens new relaxation channels,making the relaxation rate dependent on the coupling strengths.D_(y)Y_(2)N@C_(80)and D_(y)_(2)YN@C_(80)were found to be non-luminescent,while the luminescence reported for D_(y)Y_(2)N@C_(80)was caused by traces of Y3N@C_(80)and Y_(2)ScN@C_(80).
基金Marie Skłodowska-Curie actions,EU project‘SamSD’(grant agreement number 748635)European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation program(grant agreement number 648295‘GraM3’)。
文摘The detailed electronic structure of single atomic magnets is a crucial bit in the further understanding and design of a new generation of monoatomic magnetic elements on surfaces and in molecules.Control and manipulation of the single atomic state,as well as long relaxation of magnetization,have been demonstrated for lanthanide atoms on carefully chosen supporting substrates.However,these convincing experiments are puzzling by insufficient theoretical description,usually omitting the valence electrons of lanthanide atoms.In this work,starting with an idea of the inevitable need of local d-and p-shell electrons for a proper description of the magnetic states of lanthanide atoms,we rationalized the electronic structure and magnetic properties of Ho atom on the MgO substrate using ab initio multiconfigurational approaches.By doing so,we obtained the solution which complements experimental observations and has been able to pin-point the atomic state which most likely to be responsible for the exceptional magnetic properties of Ho on MgO.This study demonstrates that new paradigms are needed for understanding and interpretation of the lanthanide single-atomic magnets.
基金the European Union’s Horizon 2020 research and innovation programme,European Research Council(grant agreement no.648295 to A.A.P.)Marie Skłodowska-Curie action(grant agreement no.748635 to S.M.A.)+1 种基金the Deutsche Forschungsgemeinschaft(grants PO 1602/4-1 and 1602/5-1 to A.A.P.)the Swiss National Science Foundation(Projects No.200021L_147201 and No.206021_-150784 to T.G.)。
文摘Two isomers of metallofullerene Dy_(2)S@C_(82)with sulfur-bridged Dy ions exhibit broad magnetic hysteresis with sharp steps at sub-Kelvin temperature.Analysis of the level crossing events for different orientations of a magnetic field showed that even in powder samples,the hysteresis steps caused by quantum tunneling of magnetization can provide precise information on the strength of intramolecular Dy…Dy interactions.A comparison of different methods to determine the energy difference between ferromagnetic and antiferromagnetic states showed that sub-Kelvin hysteresis gives the most robust and reliable values.The ground state in Dy_(2)S@C_(82)has ferromagnetic coupling of Dy magnetic moments,whereas the state with antiferromagnetic coupling in C_(s)and C_(3)v cage isomers is 10.7 and 5.1 cm^(-1)higher,respectively.The value for the C_(s)isomer is among the highest found in metallofullerenes and is considerably larger than that reported in non-fullerene dinuclear molecular magnets.Magnetization relaxation times measured in zero magnetic field at sub-Kelvin temperatures tend to level off near 900 and 3200 s in C_(s)and C_(3)v isomers.These times correspond to the quantum tunneling relaxation mechanism,in which the whole magnetic moment of the Dy_(2)S@C_(82)molecule flips at once as a single entity.
