Computer model of metallic spin-glasses
Computer model of metallic spin-glasses
复制标题
金属旋转玻璃的计算机模型
DOI：
10.1103/physrevb.22.3816
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发表时间：
1977
影响因子：
3.7
通讯作者：
R. Walstedt
中科院分区：
文献类型：
--
作者：
L. Walker;R. Walstedt
用计算机模拟研究了稀释Ruderman-Kittel-Kasuya-Yosida（RKKY）耦合自旋系统的低温性质。我们的结果基于fcc晶格立方体积中随机分布的有限自旋系统的经典“基态”，该系统是通过在每一步降低系统能量的算法生成的。（海森伯）RKKY交换相互作用被认为是适当的形式在贵金属主机的本地时刻。在研究172个自旋的单个系统中出现的这种状态的数量时，我们发现在70个从不同的随机起始取向产生的状态中只有7个独立的平衡构型（EC’s）。EC的被发现具有短程角相关，这样一个适当定义的相关体积包含一个平均值的100两个邻居自旋。后一个结果被发现是独立的浓度，如预期的幂律范围函数。本文将EC交换场的分布P0（H）与在稀释极限下随机取向自旋的解析表达式进行了比较。有序化的效果是将分布加宽50%，并减少具有非常小的场的自旋的数量。在自旋波近似下导出了关于平衡态的小振荡的量子运动方程，并证明了它们与经典方程是等价的。其他功能的自旋波图片进行了讨论。与转动对称性有关的低阶模将在附录中详细讨论。计算的光谱表现为96和172自旋的系统，并发现正确的浓度缩放。本地和偶极各向异性被发现在激发谱中引入零频率间隙;然而，经典偶极项太小而不能给出明显的效果。一个类似的零频率间隙的结果，从应用程序的一个均匀的领域。治疗玻色子的激发导致一个成功的解释比热数据铜锰。对于Au Fe的情况下，一般协议也被发现，但在形式上的差异归因于近藤效应。阻尼的RKKY相互作用被发现会导致一个简单的缩放的激发频谱到较低的频率。这些结果被用来解释的比热和自旋玻璃有序温度的浓度变化的Cu Mn。我们还采用EC的96和188自旋计算零温可逆磁化率，产生良好的协议与Cu Mn数据（S= 5 2）和Au Fe数据（S= 3 2）。
The low-temperature properties of dilute Ruderman-Kittel-Kasuya-Yosida (RKKY)-coupled spin systems have been investigated by computer simulation. Our results are based upon classical" ground states" for finite systems of spins distributed randomly in a cubic volume of fcc lattice, generated by an algorithm which lowers the system energy at each step. The (Heisenberg) RKKY exchange interaction is taken to be of the form appropriate to local moments in noble-metal hosts. In studying the number of such states which occur for a single system of 172 spins, we found only seven independent equilibrium configurations (EC's) among 70 which were generated from different random starting orientations. EC's are found to possess short-range angular correlation, such that a suitably defined correlation volume contains an average of∼ two neighbor spins. The latter result is found to be independent of concentration, as expected for power-law range functions. The distribution P 0 (H) of exchange fields for EC's is compared with an analytic expression derived for randomly oriented spins in the dilute limit. The effect of ordering is to broaden the distribution by∼ 50% and to diminish the number of spins with very small fields. Quantum equations of motion for small oscillations about equilibrium are derived in a spin-wave approximation and are shown to be equivalent to their classical counterpart. Other features of the spin-wave picture are discussed. Low-lying modes related to rotational symmetry are discussed in detail in the Appendix. Calculated spectra are exhibited for systems of 96 and 172 spins and are found to scale correctly with concentration. Both local and dipolar anisotropy are found to introduce a zero-frequency gap in the excitation spectrum; the classical dipolar term is, however, too small to give an appreciable effect. A similar zero-frequency gap results from the application of a uniform field. Treating the excitations as bosons leads to a successful interpretation of specific-heat data for Cu Mn. For the case of Au Fe general agreement is also found, but with a discrepancy in form attributable to the Kondo effect. Damping of the RKKY interaction is found to cause a simple scaling of the excitation spectrum to lower frequencies. These results are used to interpret the concentration variation of the specific heat and the spin-glass ordering temperature for Cu Mn. We also employ EC's of 96 and 188 spins to calculate the zero-temperature reversible susceptibility, yielding good agreement with Cu Mn data (with S= 5 2) and Au Fe data (with S= 3 2).