Schoen Martin A W, Thonig Danny, Schneider Michael L, Silva T J, Nembach Hans T, Eriksson Olle, Karis Olof, Shaw Justin M
Quantum Electromagnetics Division, National Institute of Standards and Technology, Boulder, Colorado 80305, USA.
Institute of Experimental and Applied Physics, University of Regensburg, 93053 Regensburg, Germany.
Nat Phys. 2016;12(9). doi: 10.1038/nphys3770.
Magnetic damping is of critical importance for devices that seek to exploit the electronic spin degree of freedom, as damping strongly affects the energy required and speed at which a device can operate. However, theory has struggled to quantitatively predict the damping, even in common ferromagnetic materials. This presents a challenge for a broad range of applications in spintronics and spin-orbitronics that depend on materials and structures with ultra-low damping. It is believed that achieving ultra-low damping in metallic ferromagnets is limited by the scattering of magnons by the conduction electrons. However, we report on a binary alloy of cobalt and iron that overcomes this obstacle and exhibits a damping parameter approaching 10, which is comparable to values reported only for ferrimagnetic insulators. We explain this phenomenon by a unique feature of the band structure in this system: the density of states exhibits a sharp minimum at the Fermi level at the same alloy concentration at which the minimum in the magnetic damping is found. This discovery provides both a significant fundamental understanding of damping mechanisms and a test of the theoretical predictions proposed by Mankovsky and colleagues.
磁阻尼对于试图利用电子自旋自由度的器件至关重要，因为阻尼会强烈影响器件运行所需的能量和速度。然而，即使在常见的铁磁材料中，理论也难以定量预测阻尼。这给自旋电子学和自旋轨道电子学中广泛依赖具有超低阻尼的材料和结构的应用带来了挑战。据信，在金属铁磁体中实现超低阻尼受到传导电子对磁振子散射的限制。然而，我们报道了一种钴铁二元合金，它克服了这一障碍，其阻尼参数接近10，这与仅在亚铁磁绝缘体中报道的值相当。我们通过该系统能带结构的一个独特特征来解释这一现象：在发现磁阻尼最小值的相同合金浓度下，态密度在费米能级处呈现出一个尖锐的最小值。这一发现既为阻尼机制提供了重要的基础理解，也对曼科夫斯基及其同事提出的理论预测进行了检验。
