LaFe11.5Si1.5中的磁不稳定性

通过对LaFe11.5Si1.5化合物进行自旋极化和固定磁矩(FSM)的能带计算,发现LaFe11.5Si1.5化合物具有磁不稳定性的特征,无磁态和铁磁态的能量差别很小,FSM计算表明LaFe11.5Si1.5化合物具有低自旋态和高自旋态的双磁性态特征,在一定条件下能够在两磁性态之间发生变磁转变.通过计算的结果,定性地分析了实验上所观察的一些现象.     

Effect of Co substitution on magnetic properties and magnetic entropy changes in LaFe11.83Si0.94Al0.23 compounds

Effect of Co substitution on magnetic properties and magnetic entropy changes in LaFe_{11.83}Si_{0.94}Al_{0.23} compounds has been investigated by means of magnetization measurements. X-ray diffraction shows the prepared compounds to be single phase with the cubic NaZn_{13}-type structure. Substitution of Co for Fe leads to an increase of Curie temperature of the material. The magnetic entropy changes in LaFe_{11.83}Si_{0.94}Al_{0.23} and LaFe_{11.03}Co_{0.80}Si_{0.94}Al_{0.23} compounds are 21.8J/(kg·K) to 16.9J/(kg·K) under a magnetic field change of 0－5T at Curie temperature, respectively. Giant magnetic entropy changes are attributed to the higher magnetization and the rapid change in magnetization at Curie temperature.     

Effects of Fe－Fe bond length change in NaZn13-type intermetallic compounds on magnetic properties and magnetic entropy change

In this paper the effects of Fe－Fe bond length change on magnetic properties and magnetic entropy change have been investigated on LaFe_{12.4-x}Si_xCo_{0.6} and LaFe_{12.3-x}Al_xCo_{0.7} intermetallic compounds. According to the analyses of Fe－Fe bond length change, the variation of Curie temperature and the unusual magnetic phase transition which results in the large magnetic entropy change were explained. The effects of the substitution of Co and Si for Fe on magnetic entropy change and field-induced itinerant-electron metamagnetic transition in LaFe_{12.4-x}Si_xCo_{0.6} compounds were also studied and the considerable magnetic entropy change has been achieved.     

LaFe11.4 Al1.6中铁磁相与反铁磁相的双相共存

通过磁场下热磁曲线的测量,在LaFe11.4Al1.6化合物中发现了一个在一定温区内随温度稳定的铁磁相和反铁磁相的共存亚稳态.确定了这个亚稳态能够存在的磁场和温度范围,从而使LaFe11.4Al1.6化合物的磁相图更加完善.这个亚稳态的温度稳定性能够很好地解释磁性转变的临界场随温度的变化行为.这个双相共存亚稳态的存在,与LaFe11.4Al1.6中的磁性交换作用及晶格畸变所产生的边界相的稳定性有关.     

LaFe11.4Al1.6中铁磁相与反铁磁相的双相共存

通过磁场下热磁曲线的测量，在LaFe114Al16化合物中发现了一个在一定温区内随温度稳定的铁磁相和反铁磁相的共存亚稳态.确定了这个亚稳态能够存在的磁场和温度范围，从而使LaFe114Al16化合物的磁相图更加完善.这个亚稳态的温度稳定性能够很好地解释磁性转变的临界场随温度的变化行为.这个双相共存亚稳态的存在，与LaFe114Al16中的磁性交换作用及晶格畸变所产生的边界相的稳定性有关. 关键词： 共存相 亚稳态 晶格畸变     

Magnetic properties and magnetocaloric effect in NdxLa1-xFe11.5Al1.5 compounds

Effects of Nd-doping on the magnetic properties and magnetocaloric effects （MCEs） of NdxLa1-xFe11.5Al1.5 have been investigated. Substitution of Nd leads to a weakening of the antiferromagnetic （AFM） coupling and an enhancement of the ferromagnetic （FM） coupling. This in turn results in a complex magnetic behaviour for Nd0.2La0.8Fe11.5Al1.5 characterized by the occurrence of two phase transitions at ～188 K （PM AFM） and ～159 K （AFM-FM）. As a result, a table-like MCE （9 J/kg.K） is found in a wide temperature range （160-185 K） for a field change of 0-5T around the transition temperature, as evidenced by both the magnetic and calorimetric measurements. Based on the analysis of low-temperature heat capacity, it is found that the AFM-FM phase transition modifies the electron density significantly, and the major contribution to the entropy change comes from the electronic entropy change.