Magnetocaloric materials undergoing reversible phase transitions are highly desirable for magnetic refrigeration applications.(Mn,Fe)_(2)(P,Si)alloys exhibit a giant magnetocaloric effect accompanied by a magnetoelast...Magnetocaloric materials undergoing reversible phase transitions are highly desirable for magnetic refrigeration applications.(Mn,Fe)_(2)(P,Si)alloys exhibit a giant magnetocaloric effect accompanied by a magnetoelastic transition,while the noticeable irreversibility causes drastic degradation of the magnetocaloric properties during consecutive cooling cycles.In the present work,we performed a comprehensive study on the magnetoelastic transition of the(Mn,Fe)_(2)(P,Si)alloys by high-resolution transmission electron microscopy,in situ field-and temperature-dependent neutron powder diffraction as well as density functional theory calculations(DFT).We found a generalized relationship between the thermal hysteresis and the transition-induced elastic strain energy for the(Mn,Fe)_(2)(P,Si)family.The thermal hysteresis was greatly reduced from 11 to 1 K by a mere 4 at.%substitution of Fe by Mo in the Mn_(1.15)Fe_(0.80)P_(0.45)Si_(0.55)alloy.This reduction is found to be due to a strong reduction in the transition-induced elastic strain energy.The significantly enhanced reversibility of the magnetoelastic transition leads to a remarkable improvement of the reversible magnetocaloric properties,compared to the parent alloy.Based on the DFT calculations and the neutron diffraction experiments,we also elucidated the underlying mechanism of the tunable transition temperature for the(Mn,Fe)_(2)(P,Si)family,which can essentially be attributed to the strong competition between the covalent bonding and the ferromagnetic exchange coupling.The present work provides not only a new strategy to improve the reversibility of a first-order magnetic transition but also essential insight into the electron-spin-lattice coupling in giant magnetocaloric materials.展开更多
The development of zero and negative therma expansion(i.e.,ZTE and NTE)materials is of crucial importance to the control of undesirable thermal expansion for high-precision devices.In the present work,ZTE and NTE were...The development of zero and negative therma expansion(i.e.,ZTE and NTE)materials is of crucial importance to the control of undesirable thermal expansion for high-precision devices.In the present work,ZTE and NTE were obtained in directionally-solidified Mn_(x)Fe_(5-x)Si_(3)alloys with a strong<001>texture,in striking contrast to positive thermal expansion in their isotropic counterparts Magnetometry and in-situ X-ray diffraction(XRD)measurements were performed to uncover the origin of the anomalous thermal expansion.Magnetic measurements indicate a strong easy-plane magnetocrystalline anisotropy in the textured samples,where the magnetic moments are aligned within the ab plane of the hexagonal structure Temperature-dependent XRD on the x=1 sample reveals a ZTE character in the ab plane that is coupled to a ferromagnetic transition.As a result,the macroscopic ZTE(~0.22×10^(-6)K^(-1))in the x=1 sample can be attributed to the microscopic magneto volume effect within the ab plane,which is realized by the introduction of the<001>-textured microstructure.Besides,the competition between antiferromagnetic and ferromagnetic exchange coupling leads to NTE in textured x=1.5 and 2 samples.Additionally,textured x=1 sample displays enhanced magnetocaloric properties as compared to the conventional counterparts with randomly-oriented grains.Consequently this work demonstrates a new strategy toward the exploration of anomalous thermal expansion properties as well as the enhancement of magnetocaloric properties for materials with a strong magnetocrystalline anisotropy.展开更多
基金supported by the National Natural Science Foundation of China(Nos.51801102,U1832191,12004179,and 11974184)the Natural Science Foundation of Jiangsu Province(Nos.BK20180491 and BK20180418)+1 种基金the Open Fund of Large Facilities in Nanjing University of Science and Technologythe Guangdong-Hong Kong-Macao Joint Laboratory for Neutron Scattering Science and Technology。
文摘Magnetocaloric materials undergoing reversible phase transitions are highly desirable for magnetic refrigeration applications.(Mn,Fe)_(2)(P,Si)alloys exhibit a giant magnetocaloric effect accompanied by a magnetoelastic transition,while the noticeable irreversibility causes drastic degradation of the magnetocaloric properties during consecutive cooling cycles.In the present work,we performed a comprehensive study on the magnetoelastic transition of the(Mn,Fe)_(2)(P,Si)alloys by high-resolution transmission electron microscopy,in situ field-and temperature-dependent neutron powder diffraction as well as density functional theory calculations(DFT).We found a generalized relationship between the thermal hysteresis and the transition-induced elastic strain energy for the(Mn,Fe)_(2)(P,Si)family.The thermal hysteresis was greatly reduced from 11 to 1 K by a mere 4 at.%substitution of Fe by Mo in the Mn_(1.15)Fe_(0.80)P_(0.45)Si_(0.55)alloy.This reduction is found to be due to a strong reduction in the transition-induced elastic strain energy.The significantly enhanced reversibility of the magnetoelastic transition leads to a remarkable improvement of the reversible magnetocaloric properties,compared to the parent alloy.Based on the DFT calculations and the neutron diffraction experiments,we also elucidated the underlying mechanism of the tunable transition temperature for the(Mn,Fe)_(2)(P,Si)family,which can essentially be attributed to the strong competition between the covalent bonding and the ferromagnetic exchange coupling.The present work provides not only a new strategy to improve the reversibility of a first-order magnetic transition but also essential insight into the electron-spin-lattice coupling in giant magnetocaloric materials.
基金financially supported by the National Natural Science Foundation of China(Nos.12004179,U1832191,51801102,52271180,52001167 and 52101236)Guangdong-Hong Kong-Macao Joint Laboratory for Neutron Scattering Science and Technology+1 种基金the Fundamental Research Funds for the Central Universities(No.30922010802)the Sino-German Mobility Program from the Sino-German Center for Research Promotion(SGC)(No.M-0447)。
文摘The development of zero and negative therma expansion(i.e.,ZTE and NTE)materials is of crucial importance to the control of undesirable thermal expansion for high-precision devices.In the present work,ZTE and NTE were obtained in directionally-solidified Mn_(x)Fe_(5-x)Si_(3)alloys with a strong<001>texture,in striking contrast to positive thermal expansion in their isotropic counterparts Magnetometry and in-situ X-ray diffraction(XRD)measurements were performed to uncover the origin of the anomalous thermal expansion.Magnetic measurements indicate a strong easy-plane magnetocrystalline anisotropy in the textured samples,where the magnetic moments are aligned within the ab plane of the hexagonal structure Temperature-dependent XRD on the x=1 sample reveals a ZTE character in the ab plane that is coupled to a ferromagnetic transition.As a result,the macroscopic ZTE(~0.22×10^(-6)K^(-1))in the x=1 sample can be attributed to the microscopic magneto volume effect within the ab plane,which is realized by the introduction of the<001>-textured microstructure.Besides,the competition between antiferromagnetic and ferromagnetic exchange coupling leads to NTE in textured x=1.5 and 2 samples.Additionally,textured x=1 sample displays enhanced magnetocaloric properties as compared to the conventional counterparts with randomly-oriented grains.Consequently this work demonstrates a new strategy toward the exploration of anomalous thermal expansion properties as well as the enhancement of magnetocaloric properties for materials with a strong magnetocrystalline anisotropy.
