Dy_3Al_5O_(12)磁热性质研究  

Study on the magnetic and magnetocaloric effects of Dy_3Al_5O_(12)

作　　者：董雪[1] 张国营[1] 夏往所[1] 黄逸佳 胡风[1] 

机构地区：[1]中国矿业大学理学院物理系,徐州221008

出　　处：《物理学报》2015年第17期307-312,共6页Acta Physica Sinica

基　　金：中央高校基础研究基金(批准号:2013XK04)资助的课题~~

摘　　要：用量子理论计算了Dy_3Al_5O_(12)的晶场能谱、Zeeman劈裂能级和波函数.在外磁场H_e为0<H_e<9T,温度为3<T<42K范围内,计算了该晶体的磁矩、磁熵变,计算结果与相关实验数据吻合较好.该计算结果表明,Dy_3Al_5O_(12)内磁性离子间的交换作用非常微弱,可以忽略.从理论上给出了绝热退磁过程中温度变化△T与T的关系,并与Gd_3Ga_5O_(12)晶体进行了比较,发现不同外磁场下,Dy_3Al_5O_(12)和Gd_3Ga_5O_(12)的低温制冷性能在不同温区有差别.在进行低温(T<10K)制冷时,若外磁场较低,选择Dy_3Al_5O_(12)作为磁制冷材料较好;若外磁场较高,选择Gd_3Ga_5O_(12)作为磁制冷材料较好.The crystal field （CF）- and external magnetic field- split ground state of Dy^3＋ in Dy3Al5O12 （DyAG） has been calculated based on the quantum theory in this paper. The eight CF-split levels are obtained, which are all twofold degenerates and are removed by the external magnetic field. On the basis of the results, the magnetic moments and the magnetic entropy changes of DyAG are calculated in the temperature range of 3 〈 T 〈 42 K and the magnetic field range of 0〈H e 〈9 T. The calculated results are in good agreement with the measured data. This work shows that all of the six nonequivalent crystal sites in DyAG have contribution to the average magnetic moment and have an important impact on the magnetic anisotropy of the crystal. In addition, the study indicates that the exchange interaction between the magnetic ions in DyAG is so weak that it may be neglected. However, distinct from DyAG, the exchange interaction between the rare-earth ions in Gd3Ga5O12（GdGG） is stronger at low temperatures and dependent on the temperature and external magnetic field. Besides, the variation of the adiabatic temperature change ΔT with T is theoretically anticipated and the anticipated results are comparied with that of GdGG. It is found that the maximum adiabatic temperature change ΔT of DyAG is 1.27 times larger than that of GdGG when T = 11 K and H e = 1 T. However, it changes to 1.15 times that of GdGG when T =16 K and H e =2 T. There are differences between the refrigerative properties of DyAG and GdGG when they are in different external magnetic fields and different temperature regions. At low temperature s（T 〈 10 K）, the DyAG is a good magnetic refrigerative material in the lower external magnetic field. However, When H e is higher, GdGG is a good selection. This study is helpful to select suitable materials for the magnetic refrigeration technology.

关 键 词：Dy3Al5O12 磁矩 磁熵变 GD3GA5O12 

分 类 号：O482.5[理学—固体物理]