氧化铜公度与非公度反铁磁相变的比热研究

利用微机控制的扫描比热量热系统对氧化铜样品从液氮温度到室温作了精细的比热测量，实验在２２７Ｋ和２２１Ｋ附近检测到两个明显的比热反常，其起始转变分别发生在ＴＮ１＝２３１Ｋ和ＴＮ２＝２１３Ｋ，这两个温度值和中子磁散射室验的结果非常吻合。结合人们对ＣｕＯ单晶的中子散射实验，本文指出这两个比热异常分别对应于氧化铜非公度和公度和反铁磁，从非公度到公度的反铁磁转变为一级相变，而顺磁态到非公度反铁磁相的转变为二级相交，Ｔ＝２３０Ｋ处比热跃变量为２．３Ｊ／（ｍｏｌ·Ｋ）。

Specific-heat Anomalies of Commensurate and incommensurate Antiferromgnetic Transitions in CuO

Specific-heat measurements of cupric oxide (CuO) have been made from 80K to 260K by a sweep method.Two evident anomalies of specific heat are detected at about 227K and 211K, respectively.The onset transitions occur at TN1=231K and TN2=213K, which agree well with results of magnetic neutron scattering experiments.The experimental results indicated that the two anomalies are due to a second-order transition near 231K and a first-order one near 213K respectively. An incommensurate antiferromagnetic structure with a slightly ferromagnetic interaction forms when temperature is lower than 231K, this structure persists to 213K, then a commensurate antiferromagnetic transition occurs below 213K. The specific-heat jump AC=2.3J/(mol.K) at 230K.In the region 80K-200K the linear term of specific heat is dominant, this can be explained by the effect of the strong one-dimension magnetic correlation.