研究了在化合物Mn_1.05Ni_0.85Ge和CrO_1.86F_0.14中反铁磁向铁磁的相变对应的磁熵变, 化合物Tb₃Co中铁磁到反铁磁的相变对应的磁熵变。发现Mn_1.05Ni_0.85Ge和CrO_1.86F_0.14展示逆磁熵变，而Tb3Co中为正常磁熵变。研究了这些化合物中相变温度与外磁场的依赖关系。对代表两类不同的外磁场-温度相图的这三个化合物磁熵变化的符号做了热力学分析。讨论了其它可能的外磁场-温度相图，并对文献中报道的反铁磁-铁磁和铁磁-反铁磁的相变进行了讨论。

(a) Temperature dependencies of the ZFC and FC magnetization of Tb₃Co in a magnetic field of 0.05 T, with Tt indicating the transition temperature from AF to F. The inset displays the temperature dependence of the ZFC reduced magnetization at different magnetic fields. (b) Temperature dependence of the critical magnetic field of the AF to F transition. (c) Magnetic-entropy change at magnetic-field changes from 0 to 1 T.

(a) Magnetic isotherms of CrO_1.86F_0.14, measured from 45 to 110 K with temperature steps of 5 K. (b) Temperature dependence of the critical magnetic field of the AF to FM transition, (c) Magnetic-entropy change at magnetic-field changes from 0 to 1.5 T.