标题： 铁磁双层结构界面处的层间磁耦合微观研究 显示英文标题

标题： Microscopic study of interlayer magnetic coupling across the interface in antiferromagnetic bilayers

摘要： 在反铁磁双层结构 AF1/AF2 中，低$T_{N}$反铁磁体的 Neel 温度 ($T_N$) 的增强，其中 AF1 的$T_N$大于 AF2（例如 CoO 在 CoO/NiO 或 FeO 在 FeO/CoO 中的$T_{N}$增强），是一个备受关注的问题。 在这些双层结构中，一个基本问题需要回答：界面耦合是短程的还是长程的，从而介导 AF1 层对 AF2 层磁性性质的影响？ 为了理解界面处磁耦合的系统性，我们使用电子-空穴对称的一带 Hubbard 模型在半满填充下，采用半经典 Monte Carlo 方法研究反铁磁双层结构的平面分辨磁输运特性。 在我们的模型哈密顿量计算中，我们将库仑排斥$U_{1} = 8$设置为模拟高$T_{N}$AF1 层，而我们使用$U_{2}$=$2\times U_{1}$来模拟低$T_{N}$AF2 层。 我们的计算表明，当其厚度较小时，低$T_{N}$反铁磁体的$T_{N}$显著增强，类似于实验结果，导致双层系统的单一磁性转变温度。 这些发现得到了温度依赖比热中的单峰的良好支持。 然而，对于较大的厚度，低$T_{N}$反铁磁体的$T_{N}$趋近于其体材料值，并且组成反铁磁层在两个不同的温度下反铁磁对齐，在比热数据中观察到两个极大值。 我们的计算还表明，磁矩的离域性基本上局限于界面附近，这表明邻近效应的短程性质。 我们得到的结果与实验观察结果一致。 如果使用$U_{1} = 8$和$U_{2}$=$0.5\times U_{1}$所会发生的变化的详细讨论也将被涉及。 显示英文摘要

摘要： The enhancement of Neel temperature ($T_N$) of low-$T_{N}$ antiferromagnets in antiferromagnetic bilayers AF1/AF2, where the $T_N$ of AF1 is larger than AF2 (for example enhancement of $T_{N}$ of CoO in CoO/NiO or FeO in FeO/CoO), is a subject of considerable interest. One essential question needs to be answered in these bilayers: is the interfacial coupling a short-range one or long-range that mediates the effect of the AF1 layers on the magnetic properties of AF2 layer? To understand the systematics of the magnetic coupling across the interface, we investigate the plane-resolved magnetotransport properties of antiferromagnetic bilayers using an electron-hole symmetric one-band Hubbard model at half-filling, employing a semi-classical Monte Carlo method. In our model Hamiltonian calculations, we set Coulomb repulsion $U_{1} = 8$ to mimic high-$T_{N}$ AF1 layer, whereas we use $U_{2}$ = $2\times U_{1}$ to mimic the low-$T_{N}$ AF2 layer. Our calculations show that the $T_{N}$ of the low-$T_{N}$ antiferromagnet enhances substantially when it's thickness is small, similar to experiments, giving rise to single magnetic transition temperature of the bilayer system. These findings are well supported by a single peak in temperature-dependent specific heat. However, for larger thicknesses, the $T_{N}$ of the low-$T_{N}$ antiferromagnet approaches towards its bulk value and constituent antiferromagnetic layers align antiferromagnetically at two separate temperatures and two maxima are observed in specific heat data. Our calculations also show that the delocalization of moments is more or less confined near the interface indicating the short-ranged nature of the proximity effect. Our obtained results are consistent with the experimental observations. A detailed discussion of the modifications that will occur if we use $U_{1} = 8$ and $U_{2}$ = $0.5\times U_{1}$ will also be addressed.