London Centre for Nanotechnology and Department of Physics and Astronomy, University College London, 17-19 Gordon Street, London WC1H 0AJ, UK.
J Phys Condens Matter. 2013 Sep 4;25(35):356003. doi: 10.1088/0953-8984/25/35/356003. Epub 2013 Aug 5.
The residual entropy of spin ice and other frustrated magnets is a property of considerable interest, yet the usual way of determining it, by integrating the heat capacity, is generally ambiguous. Here we note that a straightforward alternative method based on Maxwell's thermodynamic relations can yield the residual entropy on an absolute scale. The method utilizes magnetization measurements only and hence is a useful alternative to calorimetry. We confirm that it works for the spin ice Dy₂Ti₂O₇, which recommends its application to other systems. The analysis described here also gives an insight into the dependence of entropy on magnetic moment, which plays an important role in the theory of magnetic monopoles in spin ice. Finally, we present evidence of a field-induced crossover from correlated spin ice behaviour to ordinary paramagnetic behaviour with increasing applied field, as signalled by a change in the effective Curie constant.
自旋冰和其他 frustrated magnets 的剩余熵是一个非常有趣的性质，但通常通过积分热容来确定它的方法通常是不明确的。在这里，我们注意到一种基于麦克斯韦热力学关系的直接替代方法可以在绝对标度上产生剩余熵。该方法仅利用磁化强度测量，因此是量热法的有用替代方法。我们证实它适用于自旋冰 Dy₂Ti₂O₇，这表明它可以应用于其他系统。这里描述的分析还深入了解了熵对磁矩的依赖关系，这在自旋冰中的磁单极子理论中起着重要作用。最后，我们提出了证据表明，随着外加磁场的增加，自旋冰行为与普通顺磁行为之间存在场诱导交叉，这表现为有效居里常数的变化。
