Fourth-order exchange interactions in GdxEu1-xS
Fourth-order exchange interactions in GdxEu1-xS
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DOI：
10.1016/s0304-8853(99)00474-6
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发表时间：
1999-10-01
影响因子：
2.7
通讯作者：
Brückel, T
中科院分区：
文献类型：
--
作者：
Köbler, U;Hupfeld, D;Brückel, T
本文报道了利用立方磁化率chi（3）和磁比热c（p）对GdxEu（1-xS）中四阶交换相互作用，即双二次、三自旋和四自旋相互作用的研究.在GdS的顺磁相中，这些相互作用是铁磁性的，因为chi（3）是负的（磁化强度随着磁场线性增加而增加）。在GdS的Neel温度为59 K时，已经早期观察到线性磁化率χ（1）的强场依赖性的开始。这一特征归因于四阶交换相互作用引起的准铁磁有序过程。59 K时立方磁化率χ（3）的发散提供了这方面的证据。在GdS中观察到两个进一步的磁相变：（a）在47 ° T时，磁化率和比热表现出小但确定的异常;（B）在27 ° K以下，观察到第二临界场曲线，T -> 0时仅达到2.6 T。这些相变也归因于四阶相互作用，这显然不是恒定的，而是从高温下的铁磁到低温下的反铁磁的变化。在T-N = 59 K时，GdS和EuTe的临界磁行为（磁比热c（mag））一样复杂，这是因为两种有序现象叠加在一起。用海森堡临界指数的幂律描述是不够的。在取代Gd Eu的四阶相互作用的变化，像往常一样，迅速作为组成的函数。详细研究了一个组成为Gd_（0.8）Eu_（0.2）的样品。在此样品中，在T-N = 55 K的Neel温度下，总的四级相互作用是反铁磁的。因此，在GdS中观察到的铁磁成分是不存在的，并且在55 K以下出现仅达到5.5 T的第二临界场曲线。(C)1999 Elsevier Science B. V.保留所有权利。
We report on investigations of fourth-order exchange interactions, i.e. biquadratic, three-spin and four-spin interactions in GdxEu1-xS using measurements of the cubic susceptibility chi(3) and the magnetic specific heat c(p). In the paramagnetic phase of GdS these interactions are ferromagnetic since chi(3) is negative (the magnetization increases stronger than linearly with magnetic field). At the Neel temperature of GdS of 59 K the onset of a strong field dependence of the linear susceptibility chi(1), has early been observed. This feature is attributed here to a quasi-ferromagnetic ordering process induced by the fourth-order exchange interactions. Evidence for this is provided by a divergence of the cubic susceptibility chi(3) at 59 K. Two further magnetic phase transformations were observed in GdS: (a) at 47 It the magnetic susceptibility and specific heat exhibit small but definite anomalies and, (b) below 27 K a second critical field curve reaching only 2.6 T for T --> 0 is observed. Also these phase transitions are attributed to the fourth-order interactions which apparently are not constant but change from ferromagnetic at high temperature to antiferromagnetic at low temperature. The critical magnetic behavior of the magnetic specific heat, c(mag), at T-N = 59 K is as complicated in GdS as in EuTe because two ordering phenomena superpone. A description by power laws with Heisenberg critical exponents is inadequate. On substituting Gd by Eu fourth-order interactions change, as usual, rapidly as function of composition. One sample with composition Gd0.8Eu0.2 was investigated in detail. In this sample the total fourth-order interaction is antiferromagnetic at the Neel temperature of T-N = 55 K. As a consequence, the ferromagnetic component observed in GdS is absent and a second critical field curve reaching only 5.5 T occurs below 55 K. (C) 1999 Elsevier Science B.V. All rights reserved.