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首页> 外文期刊>Journal of Physics, D. Applied Physics: A Europhysics Journal >Temperature dependence of the effective anisotropies in magnetic nanoparticles with Néel surface anisotropy
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Temperature dependence of the effective anisotropies in magnetic nanoparticles with Néel surface anisotropy

机译：具有Néel表面各向异性的磁性纳米粒子中有效各向异性的温度依赖性

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摘要

We discuss the physical concept of the effective anisotropy in magnetic nanoparticles with surface anisotropy. A recently developed constrained Monte Carlo method allows evaluation of the temperature dependence of the energy surface in the whole temperature range, from which the effective anisotropy is determined. We consider nanoparticles of different shapes with cubic or uniaxial core anisotropy and Néel surface anisotropy. We demonstrate that at low temperatures surface effects can be dominant, leading to an overall cubic effective anisotropy even in spherical nanoparticles with uniaxial core anisotropy. This cubic anisotropy contribution decreases more rapidly with increasing temperature than the uniaxial core anisotropy, leading to a temperature-induced reorientation transition. We discuss the scaling behaviour of the effective anisotropy with magnetization in nanoparticles with surface anisotropy contribution. The scaling exponent deviates from that expected from Callen-Callen theory due to increased fluctuations of the surface spins.
机译：我们讨论具有表面各向异性的磁性纳米粒子中有效各向异性的物理概念。最近开发的约束蒙特卡洛方法允许评估整个温度范围内能量表面的温度依赖性，由此确定有效的各向异性。我们考虑具有立方或单轴核各向异性和Néel表面各向异性的不同形状的纳米颗粒。我们证明，在低温下，表面效应可能占主导地位，甚至在具有单轴核各向异性的球形纳米粒子中也导致整体立方有效各向异性。这种立方各向异性的贡献随着温度的升高比单轴纤芯的各向异性下降得更快，从而导致温度引起的取向转变。我们讨论了具有各向异性的纳米粒子在磁化作用下有效各向异性的定标行为。由于表面自旋的波动增加，结垢指数偏离了卡伦-卡伦理论的预期。

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