Polarised Neutron Reflection Studies of Thin Magnetic Films
Polarised Neutron Reflection Studies of Thin Magnetic Films
复制标题
磁性薄膜的偏振中子反射研究
DOI：
10.1007/3-540-27163-5_7
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发表时间：
2005
影响因子：
3.7
通讯作者：
C. Vaz
中科院分区：
文献类型：
--
作者：
J. A. C. Bland;C. Vaz
磁矩是磁性中最基本的量，但对于薄膜来说，测量磁矩却是最具实验挑战性的量。磁序对应于电子角动量的微观有序，无论它是定域原子轨道和自旋矩和/或巡回带电子的自旋矩。这种有序态对应于与高能热激发态相比能量较低的态。磁矩的大小一方面取决于角矩的大小(特别是对于局域系统)，另一方面取决于多数和少数电子带之间的自旋不平衡。对于3d过渡金属，强晶场猝灭了轨道磁矩，磁矩主要由电子自旋引起。对于4f系列，轨道矩不是猝灭的，对磁矩的主要贡献来自原子角矩。此外，在这两种情况下，负责磁序的机制是不同的。由于尺寸减小的电子结构的变化，磁矩半径不一定随系统的体积而变化。事实上，可以预料的是，随着系统的物理尺寸减小，对称性的破缺会导致靠近界面的那些原子的波函数局域化。虽然这种对称性破缺对磁各向异性的影响非常显著，但通常对磁矩的影响较小，更难观察到。此外，亚稳态晶体结构可以稳定在薄的外延薄膜或小颗粒中，这些薄膜或小颗粒通常表现出与体平衡相对应的不同的磁矩。此外，现在越来越多的人认识到，界面力矩在决定磁性设备的行为中是至关重要的，例如，磁隧道结，特别是‘埋藏的界面’对这种设备的成功性能至关重要。虽然材料的磁矩通常是在块状材料中测量的，但
The magnetic moment is the most fundamental quantity in magnetism and yet the most experimentally challenging quantity to measure in the case of thin films. Magnetic order corresponds to the microscopic ordering of the electron angular momentum, be it the localised atomic orbital and spin moment and/or the spin moment of itinerant band electrons. Such ordered states correspond to states of lower energy compared with higher energy thermally excited states. The magnitude of the magnetic moment depends, on the one hand, on the magnitude of the angular moment (in particular for localised systems) and on the other on the spin imbalance between majority and minority electron bands. For the 3d transition metals the orbital moment is quenched by the strong crystal field and the magnetic moment is mostly due to the electron spin. For the 4f series, the orbital moment is not quenched, and the main contribution to the magnetic moment comes from the atomic angular moment. Additionally, the mechanisms responsible for the magnetic order are different in these two situations. Due to changes in electronic structure with reduced dimensions, the magnetic moment ariadoes not necessarily scale with the volume of the system. In fact, it is expected that as the physical dimensions of the system are reduced, the break in symmetry induces a localisation of the wavefunction of those atoms close to the interface. While the effect of this symmetry break on the magnetic anisotropy is very pronounced, the effect on the magnetic moment is in general smaller and more difficult to observe. Also, metastable crystal structures can be stabilised in thin epitaxial films or small particles, which often exhibit magnetic moments which are different from those corresponding to the bulk equilibrium phase. Furthermore, it is now increasingly recognized that the interface moment is crucial in determining the behaviour of magnetic devices, eg, magnetic tunnel junctions and in particular ‘buried interfaces’ are critical to the successful performance of such devices. While the magnetic moment of materials have been measured routinely in the bulk, the