磁性弛豫铁电体CdCr_2S_4的磁熵特性研究

Magnetocaloric effect in magnetic relaxor CdCr_2S_4

磁性弛豫铁电材料是指在一定温度范围内同时具有弛豫铁电性和铁磁(反铁磁)序的材料,弛豫铁电性和磁有序的共存使其存在内禀的磁电效应.实验上已经测出在外加磁场情况下磁性弛豫铁电材料CdCr2S4具有巨大的磁熵效应,但是理论上还没有具体解释这一现象.本文分别运用球形无规键-无规场模型(SRBRF模型)和海森堡模型(Heisenberg模型)来描述铁电子系统和磁子系统,并且考虑了两个子系统之间的耦合相互作用,研究了外加磁场及温度的大小对磁性弛豫铁电材料CdCr2S4的磁熵变化及绝热温度差的改变.研究表明,磁熵变化及绝热温度差都在磁相变温度附近具有最大值,我们的理论研究结果很好地解释了实验现象.

Magnetic relaxor ferroelectric materials are compounds in which the relaxor ferroelectricity and ferromagnetic（antiferromagnetic） order coexist simultaneously in certain temperature range.The coexistence of the two order parameters may result in the inherent magnetoelectric effect.Colossal magnetocaloric effect of magnetic relaxor CdCr2S4 was investigated experimentally,but theoretical studies have not been reported.Therefore,we explore theoretically the magnetocaloric effect of magnetic relaxor CdCr2S4,combining the relaxor ferroelectric subsysterm and the magnetic subsysterm.In addition,the coupling interaction between the two subsysterms is concerned.It is found that both the entropy change and the adiabatic temperature change show the maximum near the magnetic phase transition temperature,which is in good agreement with the experimental results.