School of Physical, Environmental and Mathematical Sciences, The University of New South Wales, The Australian Defence Force Academy, Canberra ACT, Australia.
J Phys Condens Matter. 2011 Jun 1;23(21):216002. doi: 10.1088/0953-8984/23/21/216002. Epub 2011 May 9.
The structural and magnetic properties of the TbNi(2)Mn(x) series (0.9 ≤ x ≤ 1.10) have been investigated using x-ray diffraction, field- and temperature-dependent AC magnetic susceptibility, DC magnetization (5-340 K; 0-5 T) and (57)Fe Mössbauer spectroscopy (5-300 K). TbNi(2)Mn(x) crystallizes in the MgCu(2)-type structure (space group Fd3m). The additional contributions to the magnetic energy terms from transition-metal-transition-metal interactions (T-T) and rare-earth-transition-metal interactions (R-T) in RNi(2)Mn compounds contribute to their increased magnetic ordering temperatures compared with RNi(2) and RMn(2). Both the lattice constant a and the Curie temperature T(C) exhibit maximal values at the x = 1 composition indicating strong magnetostructural coupling. Analyses of the AC magnetic susceptibility and DC magnetization data of TbNi(2)Mn around the Curie temperature T(C) = 147 K confirm that the magnetic transition is second order with critical exponents β = 0.77 ± 0.12, γ = 1.09 ± 0.07 and δ = 2.51 ± 0.06. These exponents establish that the magnetic interactions in TbNi(2)Mn are long range despite mixed occupancies of Tb and Mn atoms at the 8a site and vacancies. The magnetic entropy - ΔS(M) around T(C) is proportional to (μ(0)H/T(C))(2/3) in agreement with the critical magnetic analyses. The Mössbauer spectra above T(C) are fitted by two sub-spectra in agreement with refinement of the x-ray data while below T(C) three sub-spectra are required to represent the three inequivalent local magnetic environments.
已经使用 X 射线衍射、场和温度相关的交流磁化率、直流磁化（5-340 K；0-5 T）和 57Fe Mössbauer 光谱（5-300 K）研究了 TbNi(2)Mn(x) 系列（0.9≤x≤1.10）的结构和磁性。TbNi(2)Mn(x) 结晶为 MgCu(2)- 型结构（空间群 Fd3m）。与 RNi(2) 和 RMn(2) 相比，RNi(2)Mn 化合物中过渡金属-过渡金属相互作用（T-T）和稀土-过渡金属相互作用（R-T）对磁能项的额外贡献导致其磁有序温度增加。晶格常数 a 和居里温度 T(C) 在 x = 1 组成时表现出最大值，表明强磁结构耦合。在居里温度 T(C) = 147 K 附近，对 TbNi(2)Mn 的交流磁化率和直流磁化数据的分析证实，磁转变是二级的，临界指数β=0.77±0.12，γ=1.09±0.07，δ=2.51±0.06。这些指数表明，尽管 Tb 和 Mn 原子在 8a 位和空位处混合占据，但 TbNi(2)Mn 中的磁相互作用是长程的。在 T(C) 周围的磁熵 - ΔS(M)与 (μ(0)H/T(C))(2/3) 成正比，与临界磁分析一致。在 T(C) 以上，Mössbauer 光谱由两个子谱拟合，与 X 射线数据的细化一致，而在 T(C) 以下，需要三个子谱来表示三个不等价的局部磁环境。
