Cuñado José Luis F, Bollero Alberto, Pérez-Castañeda Tomás, Perna Paolo, Ajejas Fernando, Pedrosa Javier, Gudín Adrian, Maldonado Ana, Niño Miguel Angel, Guerrero Rubén, Cabrera David, Terán Francisco J, Miranda Rodolfo, Camarero Julio
Departamento de Física de la Materia Condensada and Instituto "Nicolás Cabrera", Universidad Autónoma de Madrid, Madrid, Spain.
Instituto Madrileño de Estudios Avanzados en Nanociencia IMDEA-Nanociencia, Campus Universidad Autónoma de Madrid, Madrid, Spain.
Sci Rep. 2017 Oct 18;7(1):13474. doi: 10.1038/s41598-017-13854-7.
The Stoner-Wohlfarth (SW) model is the simplest model that describes adequately the magnetization reversal of nanoscale systems that are small enough to contain single magnetic domains. However for larger sizes where multi-domain effects are present, e.g., in thin films, this simple macrospin approximation fails and the experimental critical curve, referred as SW astroid, is far from its predictions. Here we show that this discrepancy could vanish also in extended system. We present a detailed angular-dependent study of magnetization reversal dynamics of a thin film with well-defined uniaxial magnetic anisotropy, performed over 9 decades of applied field sweep rate (dH/dt). The angular-dependent properties display a gradual transition from domain wall pinning and motion-like behaviour to a nucleative single-particle one, as dH/dt increases. Remarkably, in the high dynamic regime, where nucleation of reversed domains is the dominant mechanism of the magnetization reversal (nucleative regime), the magnetic properties including the astroid become closer to the ones predicted by SW model. The results also show why the SW model can successfully describe other extended systems that present nucleative regime, even in quasi-static conditions.
斯托纳 - 沃尔法思（SW）模型是能够充分描述纳米尺度系统磁化反转的最简单模型，这类纳米尺度系统小到足以包含单个磁畴。然而，对于存在多畴效应的较大尺寸系统，例如在薄膜中，这种简单的宏观自旋近似就失效了，实验得到的临界曲线（称为SW星状曲线）与该模型的预测相差甚远。在此我们表明，这种差异在扩展系统中也可能消失。我们对具有明确单轴磁各向异性的薄膜的磁化反转动力学进行了详细的角度相关研究，研究范围涵盖了9个数量级的外加磁场扫描速率（dH/dt）。随着dH/dt的增加，角度相关特性呈现出从畴壁钉扎和类似运动行为到成核单粒子行为的逐渐转变。值得注意的是，在高动态区域，即反向畴的成核是磁化反转的主导机制（成核区域）时，包括星状曲线在内的磁性特性变得更接近SW模型所预测的结果。研究结果还表明了为什么SW模型即使在准静态条件下也能成功描述其他呈现成核区域的扩展系统。
