论文标题
SMFE $ _ {12} $的有限温度磁性特性的统计和分析方法
Statistical and Analytical Approaches to Finite Temperature Magnetic Properties of SmFe$_{12}$
论文作者
论文摘要
为了研究SMFE $ _ {12} $的磁性特性，我们构建了一个有效的自旋模型，其中磁矩，晶体场（CF）参数和0 K的交换场由第一原理确定。使用此模型研究有限温度磁性。我们进一步开发了一种分析方法，即具有不同量子数量的角动量$ j $（$ j $ - 浓度）的强烈混合，这是由强大的交换场作用于4 $ f $电子的旋转组件上的。将我们的分析结果与Boltzmann统计数据计算的结果进行比较，我们澄清说，先前针对SM过渡金属化合物的分析研究过高地估计了$ J $混合效应。目前的方法使我们能够对具有高可靠性的磁各向异性（MA）的温度依赖性进行定量分析。具有模型近似值的分析方法表明，由交换场引起的$ j $混合增加了旋转角动量，从而通过自旋轨道相互作用增强了轨道角动量和MA常数的绝对值。还澄清说，这些混合效应甚至超过室温。 Smfe $ _ {12} $的磁化显示了被称为一阶磁化过程（FOMP）的特殊场依赖性，其中磁化强度在某些磁场上显示出突然的变化。分析的结果表明，FOMP的起源归因于竞争性MA常数在正$ k_1 $和负$ k_2 $之间。出现$ k_ {1（2）} $的迹象是由于参数$ a_2^0 \ langle r^2 \ rangle $（$ a_4^0 \ langle r^4 \ rangle $）在3 $ d $ $ i $ i $ i $ i $ i $ j $ i $ j $ j $ j $ j $ j $ j $ i $ j $ j $ j $ j $（8 $ i）引起SM网站。可以验证的是，fomp的出现要求为$ -K_2 <k_1 <-6k_2 $。
To investigate the magnetic properties of SmFe$_{12}$, we construct an effective spin model, where magnetic moments, crystal field (CF) parameters, and exchange fields at 0 K are determined by first principles. Finite temperature magnetic properties are investigated by using this model. We further develop an analytical method with strong mixing of states with different quantum number of angular momentum $J$ ($J$-mixing), which is caused by strong exchange field acting on spin component of 4$f$ electrons. Comparing our analytical results with those calculated by Boltzmann statistics, we clarify that the previous analytical studies for Sm transition metal compounds over-estimate the $J$-mixing effects. The present method enables us to make quantitative analysis of temperature dependence of magnetic anisotropy (MA) with high-reliability. The analytical method with model approximations reveals that the $J$-mixing caused by exchange field increases spin angular momentum, which enhances the absolute value of orbital angular momentum and MA constants via spin-orbit interaction. It is also clarified that these J-mixing effects remain even above room temperature. Magnetization of SmFe$_{12}$ shows peculiar field dependence known as first-order magnetization process (FOMP), where the magnetization shows an abrupt change at certain magnetic field. The result of the analysis shows that the origin of FOMP is attributed to competitive MA constants between positive $K_1$ and negative $K_2$. The sign of $K_{1(2)}$ appears due to an increase in CF potential denoted by the parameter $A_2^0\langle r^2\rangle$ ($A_4^0\langle r^4\rangle$) caused by hybridization between 3$d$-electrons of Fe on 8$i$ (8$j$) site and 5$d$ and 6$p$ valence electrons on Sm site. It is verified that the requirement for the appearance of FOMP is given as $-K_2<K_1<-6K_2$.
