本文研究了4d过渡族金属Zr取代(Mn,Fe)2 (P,Si)合金中Fe原子对其晶体结构、居里温度、热滞以及磁热性能的影响规律。结果显示,当Zr取代10at.%的Fe时,可将MnFeP0.65Si0.35原始样品的热滞由18 K降低至1.5K,大大提高其相变的可逆性。然而,...本文研究了4d过渡族金属Zr取代(Mn,Fe)2 (P,Si)合金中Fe原子对其晶体结构、居里温度、热滞以及磁热性能的影响规律。结果显示,当Zr取代10at.%的Fe时,可将MnFeP0.65Si0.35原始样品的热滞由18 K降低至1.5K,大大提高其相变的可逆性。然而,当Zr原子的含量增加至20 at.%时,热滞出现了上升,这主要由于过量的Zr造成了Mn5Si3型第二相的出现,消耗了主相中的部分Si原子所致。与此同时,随着Zr含量的增加,居里温度逐渐上升。这是由于Zr取代部分Fe原子削弱了(Mn,Fe)2 (P,Si)合金中Fe-Si的化学键合作用,增强了铁磁相的稳定性,从而提高了该合金的居里温度。此外,Zr掺杂的(Mn,Fe)2 (P,Si)合金仍然表现出较强的磁热性能。因此,Zr掺杂的(Mn,Fe)2 (P,Si)合金因其具有较小的热滞、可调的居里温度以及优异的磁热性能有望应用于室温磁制冷和能量转换领域。 Theinfluence of 4d transition metal Zr substitution on the structure,magnetoelastic transition and magnetocaloric properties has been investigatedfor the MnFe1-xZrxP0.65Si0.35alloys. The substitution for Fe by 10 at.% Zr significantly diminishes the thermalhysteresis (ΔThvs) from 18 to 1.5 K and hence greatlyenhances the reversibility of the magnetoelastic transition. However, a furtherincrease in the Zr content to 20 at.% deteriorates the thermal hysteresis. Thisis due to the formation of Mn5 Si3-type impurity phase, which depletes the Si atoms in the main phase. The Curietemperature (TC) is raised with the increasing Zrcontent. This is due to the Zr-induced weakening of the Fe-Si covalent bonding,which stabilizes the ferromagnetic state and thus increases the TC.Additionally, the giant magnetocaloric effect (MCE) is retained in theZr-substituted samples. Consequently, the combination of small ΔThvs,tunable TC and giant MCE has made the Zr-substituted (Mn,Fe)2 (P,Si) promising for room-temperature magnetic refrigerationand energy conversion applications.展开更多
The Mn Fe P0.56Si0.44 compound is investigated by x-ray diffraction, magnetic measurements, and x-ray absorption fine structure spectroscopy. It crystallizes in Fe2P-type structure with the lattice parameters a = b = ...The Mn Fe P0.56Si0.44 compound is investigated by x-ray diffraction, magnetic measurements, and x-ray absorption fine structure spectroscopy. It crystallizes in Fe2P-type structure with the lattice parameters a = b = 5.9823(0) and c = 3.4551(1) and undergoes a first-order phase transition at the Curie temperature of 255 K. The Fe K edge and Mn K edge x-ray absorption fine structure spectra show that Mn atoms mainly reside at 3g sites, while 3f sites are occupied by Fe atoms. The distances between the absorbing Fe atom and the first and second nearest neighbor Fe atoms in a 3f-layer shift from 2.65 and 4.01 in the ferromagnetic state to 2.61 and 3.96 in the paramagnetic phase. On the other hand, the distance between the 3g-layer and 3f-layer changes a little as 2.66 –2.73 below the Curie temperature and2.68 –2.75 above it.展开更多
（MnFe）2（P, Si）-type compounds are, to date, one of the best candidates for magnetic refrigeration and energy conversion applications due to the combination of giant magnetocaloric effect （MCE）, tunable working t...（MnFe）2（P, Si）-type compounds are, to date, one of the best candidates for magnetic refrigeration and energy conversion applications due to the combination of giant magnetocaloric effect （MCE）, tunable working temperature range and low material cost. The giant MCE in the （Mn, Fe）2（P, Si）-type compounds originates from strong mag- netoelastic coupling, where the lattice degrees of freedom and spin degrees of freedom are efficiently coupled. The tunability of the phase transition, in terms of the critical temperature and the character of the phase transition, is essentially attributed to the changes in the magnetoelastic coupling in the （Mn, Fe）2（P, Si）-type compounds. In this review, not only the fundamentals of the magnetoelastic coupling but also the related practical aspects such as magnetocaloric performance, hysteresis issue and mechanical stability are discussed for the （Mn, Fe）2（P, Si）- type compounds. Additionally, some future fundamental studies on the MCE as well as possible ways of solving the hysteresis and fracture issues are proposed.展开更多
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
文摘本文研究了4d过渡族金属Zr取代(Mn,Fe)2 (P,Si)合金中Fe原子对其晶体结构、居里温度、热滞以及磁热性能的影响规律。结果显示,当Zr取代10at.%的Fe时,可将MnFeP0.65Si0.35原始样品的热滞由18 K降低至1.5K,大大提高其相变的可逆性。然而,当Zr原子的含量增加至20 at.%时,热滞出现了上升,这主要由于过量的Zr造成了Mn5Si3型第二相的出现,消耗了主相中的部分Si原子所致。与此同时,随着Zr含量的增加,居里温度逐渐上升。这是由于Zr取代部分Fe原子削弱了(Mn,Fe)2 (P,Si)合金中Fe-Si的化学键合作用,增强了铁磁相的稳定性,从而提高了该合金的居里温度。此外,Zr掺杂的(Mn,Fe)2 (P,Si)合金仍然表现出较强的磁热性能。因此,Zr掺杂的(Mn,Fe)2 (P,Si)合金因其具有较小的热滞、可调的居里温度以及优异的磁热性能有望应用于室温磁制冷和能量转换领域。 Theinfluence of 4d transition metal Zr substitution on the structure,magnetoelastic transition and magnetocaloric properties has been investigatedfor the MnFe1-xZrxP0.65Si0.35alloys. The substitution for Fe by 10 at.% Zr significantly diminishes the thermalhysteresis (ΔThvs) from 18 to 1.5 K and hence greatlyenhances the reversibility of the magnetoelastic transition. However, a furtherincrease in the Zr content to 20 at.% deteriorates the thermal hysteresis. Thisis due to the formation of Mn5 Si3-type impurity phase, which depletes the Si atoms in the main phase. The Curietemperature (TC) is raised with the increasing Zrcontent. This is due to the Zr-induced weakening of the Fe-Si covalent bonding,which stabilizes the ferromagnetic state and thus increases the TC.Additionally, the giant magnetocaloric effect (MCE) is retained in theZr-substituted samples. Consequently, the combination of small ΔThvs,tunable TC and giant MCE has made the Zr-substituted (Mn,Fe)2 (P,Si) promising for room-temperature magnetic refrigerationand energy conversion applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.51461035,51161017,and 11404176)the Scientific Research Projects of the Higher Educational Department of Inner Mongolian Autonomous Region,China(Grant No.NJZZ14033)The XAFS measurement was performed under the approval of Photon Factory Program Advisory Committee(Proposal Nos.2012G095 and 2014G047)
文摘The Mn Fe P0.56Si0.44 compound is investigated by x-ray diffraction, magnetic measurements, and x-ray absorption fine structure spectroscopy. It crystallizes in Fe2P-type structure with the lattice parameters a = b = 5.9823(0) and c = 3.4551(1) and undergoes a first-order phase transition at the Curie temperature of 255 K. The Fe K edge and Mn K edge x-ray absorption fine structure spectra show that Mn atoms mainly reside at 3g sites, while 3f sites are occupied by Fe atoms. The distances between the absorbing Fe atom and the first and second nearest neighbor Fe atoms in a 3f-layer shift from 2.65 and 4.01 in the ferromagnetic state to 2.61 and 3.96 in the paramagnetic phase. On the other hand, the distance between the 3g-layer and 3f-layer changes a little as 2.66 –2.73 below the Curie temperature and2.68 –2.75 above it.
基金financially supported by the Key Research & Development Program of Jiangsu Province(No.BE2017102)
文摘（MnFe）2（P, Si）-type compounds are, to date, one of the best candidates for magnetic refrigeration and energy conversion applications due to the combination of giant magnetocaloric effect （MCE）, tunable working temperature range and low material cost. The giant MCE in the （Mn, Fe）2（P, Si）-type compounds originates from strong mag- netoelastic coupling, where the lattice degrees of freedom and spin degrees of freedom are efficiently coupled. The tunability of the phase transition, in terms of the critical temperature and the character of the phase transition, is essentially attributed to the changes in the magnetoelastic coupling in the （Mn, Fe）2（P, Si）-type compounds. In this review, not only the fundamentals of the magnetoelastic coupling but also the related practical aspects such as magnetocaloric performance, hysteresis issue and mechanical stability are discussed for the （Mn, Fe）2（P, Si）- type compounds. Additionally, some future fundamental studies on the MCE as well as possible ways of solving the hysteresis and fracture issues are proposed.
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National Natural Science Foundation of China(61361008)National Key Basic Research Development Program of China("973" Program)(2010CB635112)Graduate Innovation Special Fund of Jiangxi Province(YC2016-B007)
