Departamento de Física da Universidade do Porto, Rua do Campo Alegre 687, Porto, Portugal.
J Phys Condens Matter. 2010 Apr 7;22(13):136002. doi: 10.1088/0953-8984/22/13/136002. Epub 2010 Mar 12.
The specific heat (C(T)) of Gd₄Co₃ was measured in the temperature range 2-300 K and its magnetic contribution (C(m)(T)) was determined using a new method that fits the electronic specific heat coefficient (γ) and the Debye temperature (θ(D)) by constraining the resulting magnetic entropy (S(m)(T)) to saturate at temperatures far above the Curie temperature (T(C)). C(m)(T) exhibits a low-temperature bump originating from thermal excitation of gapped spin waves, which is responsible for pronounced peaks, at ≈35 K, in both C(m)/T and the temperature derivative of the magnetic contribution to electrical resistivity (dρ(m)/dT). Apart from in the vicinity of T(C), an excellent global correlation was found between C(m)/T and dρ(m)/dT. Our results provide strong support for the consistency of the new method proposed for the determination of C(m)(T) and rule out any major role of short-range order on Gd moments or d-electron spin fluctuation effects in the paramagnetic phase. A comparative analysis with other methods used in similar compounds points to the need for a better evaluation of C(m)(T) in such compounds, especially in the magnetically ordered phase, where a deficient evaluation of C(m)/T has a larger impact on the S(m)(T) curve.
在 2-300 K 的温度范围内测量了 Gd₄Co₃ 的比热容（C(T)），并使用一种新方法确定了其磁贡献（C(m)(T)），该方法通过约束得到的磁熵（S(m)(T)）在远高于居里温度（T(C)）的温度下饱和来确定电子比热系数（γ）和德拜温度（θ(D)）。C(m)(T) 表现出低温凸起，这是由间隙自旋波的热激发引起的，这导致了在 ≈35 K 时 C(m)/T 和磁对电阻率的温度导数（dρ(m)/dT）都出现明显的峰值。除了在 T(C)附近，还发现 C(m)/T 和 dρ(m)/dT 之间存在极好的整体相关性。我们的结果为确定 C(m)(T) 的新方法的一致性提供了有力支持，并排除了短程有序对 Gd 磁矩或顺磁相中 d 电子自旋涨落效应的任何主要作用。与类似化合物中使用的其他方法的比较分析表明，需要更好地评估此类化合物中的 C(m)(T)，特别是在磁有序相中，对 C(m)/T 的评估不足会对 S(m)(T)曲线产生更大的影响。
