化学无序对L1 $_0$ - FeNi（四氯铅矿）中磁交换相互作用的影响
Impact of chemical disorder on magnetic exchange interactions in L1$_0$-FeNi (tetrataenite)
摘要：
利用基于第一性原理的计算方法研究了化学无序对L1 $_0$有序FeNi中磁交换耦合和居里温度（$T_{\text{c}}$）的影响.我们使用超原胞来模拟化学无序，以解释单个原子周围特定的局部化学环境。我们发现一个非常强大的变化的最主要的第一近邻Fe-Fe相互作用不同的不等价的Fe-Fe对，范围从约5毫电子伏至37毫电子伏，相比，在有序状态的耦合强度为27毫电子伏。为了估计这种强烈的磁耦合常数的变化对无序或部分有序状态的居里温度的影响，我们研究了一个简单的海森堡模型与随机高斯分布最近邻耦合的fcc晶格。我们的蒙特卡罗模拟这个模型表明，强烈变化的交换耦合，如FeNi获得的，可以导致约10%的减少$T_{\text{c}}$相对于一个只使用平均耦合。
英文摘要：
We investigate the effect of chemical disorder on the magnetic exchange couplings and the Curie temperature ($T_{\text{c}}$) in L1$_0$-ordered FeNi using first-principles-based calculations. We use supercells to model chemical disorder, to account for the specific symmetry-broken local chemical environments around the individual atoms. We find a very strong variation of the most dominant first-nearest neighbor Fe-Fe interaction for different inequivalent Fe-Fe pairs, ranging from around 5 meV to 37 meV, compared to a coupling strength of 27 meV in the ordered state. To estimate the influence of such strong variations of the magnetic coupling constants on the Curie temperature of the disordered or partially ordered state, we study a simple Heisenberg model with random Gaussian-distributed nearest neighbor couplings on an fcc lattice. Our Monte Carlo simulations for this model indicate that strongly varying exchange couplings, such as those obtained for FeNi, can lead to a reduction of $T_{\text{c}}$ of around 10% relative to the one obtained using only the average coupling.
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