Antiferromagnetic phase transition in garnet-type AgCa2Co2V3O12 and AgCa2Ni2V3O12
Antiferromagnetic phase transition in garnet-type AgCa2Co2V3O12 and AgCa2Ni2V3O12
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石榴石型 AgCa2Co2V3O12 和 AgCa2Ni2V3O12 中的反铁磁相变
DOI：
10.1016/j.jpcs.2004.11.006
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发表时间：
2005
期刊：
影响因子：
--
通讯作者：
S. Nagata
中科院分区：
文献类型：
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作者：
J. Awaka;Masakazu Ito;Takashi Suzuki;S. Nagata
在两种钒石榴石AgCa_2Co_2V_3O_（12）和AgCa_2Ni_2V_3O_（12）中发现并研究了反铁磁相变。由于反铁磁序的存在，热容出现尖峰，其Néel温度TN分别为6.39K（AgCa 2Co 2 V3 O 12）和7.21K（AgCa 2Ni 2 V3 O 12）.磁化率具有宽的最大值，这些TN对应于磁化率χ稍低于T（χmax）的拐点。从0到20 K，每摩尔Co2+和Ni 2+离子的磁熵变分别为5.31JK-1 mol-Co2 +-ion-1和6.85JK-1 mol-Ni 2 +-ion-1，表明Co2+离子的S=1/2，Ni 2+离子的S=1。AgCa 2Ni 2 V3 O 12的磁化率在20 ~ 350 K之间表现为Curie-韦斯行为，有效磁矩μeff=3.23μ BNi 2 +-ion− 1，韦斯常数θ=− 16.4 K（反铁磁符号）。然而，简单的Curie-Weiss定律不适用于AgCa 2Co 2 V3 O 12。本文在晶体电场的基础上，用Tanabe-Sugano能量图解释了磁化率与温度的复杂关系。基态是自旋二重态2 E（t26 e），第一激发态是自旋四重态4 T1（t25 e2），其位置非常接近基态。实验证实Co ~（2+）离子的低自旋态S=1/2至少在20 K以下，这与热容的结果一致。
Antiferromagnetic phase transition in two vanadium garnets AgCa2Co2V3O12and AgCa2Ni2V3O12has been found and investigated extensively. The heat capacity exhibits sharp peak due to the antiferromagnetic order with the Néel temperature TN=6.39K for AgCa2Co2V3O12and 7.21K for AgCa2Ni2V3O12, respectively. The magnetic susceptibilities exhibit broad maximum, and these TNcorrespond to the inflection points of the magnetic susceptibility χ a little lower than T(χmax). The magnetic entropy changes from zero to 20K per mol Co2+and Ni2+ions are 5.31JK−1mol-Co2+-ion−1and 6.85JK−1mol-Ni2+-ion−1, indicating S=1/2 for Co2+ion and S=1 for Ni2+ion. The magnetic susceptibility of AgCa2Ni2V3O12shows the Curie-Weiss behavior between 20 and 350K with the effective magnetic moment μeff=3.23μBNi2+-ion−1and the Weiss constant θ=−16.4K (antiferromagnetic sign). Nevertheless, the simple Curie-Weiss law cannot be applicable for AgCa2Co2V3O12. The complex temperature dependence of magnetic susceptibility has been interpreted within the framework of Tanabe-Sugano energy diagram, which is analyzed on the basis of crystalline electric field. The ground state is the spin doublet state2E(t26e) and the first excited state is spin quartet state4T1(t25e2) which locates extremely close to the ground state. The low spin state S=1/2 for Co2+ion is verified experimentally at least below 20K which is in agreement with the result of the heat capacity.