1] Department of Physics, New York University, New York, New York 10003, USA [2] Grup de Magnetisme, Departament de Física Fonamental, Universitat de Barcelona, Spain.
Department of Physics, New York University, New York, New York 10003, USA.
Nat Nanotechnol. 2014 Dec;9(12):992-6. doi: 10.1038/nnano.2014.255. Epub 2014 Nov 17.
Magnetic thin films with perpendicular magnetic anisotropy have localized excitations that correspond to reversed, dynamically precessing magnetic moments, which are known as magnetic droplet solitons. Fundamentally, these excitations are associated with an attractive interaction between elementary spin-excitations and have been predicted to occur in perpendicularly magnetized materials in the absence of damping. Although damping suppresses these excitations, it can be compensated by spin-transfer torques when an electrical current flows in nanocontacts to ferromagnetic thin films. Theory predicts the appearance of magnetic droplet solitons in nanocontacts at a threshold current and, recently, experimental signatures of droplet nucleation have been reported. However, to date, these solitons have been observed to be nearly reversible excitations, with only partially reversed magnetization. Here, we show that magnetic droplet solitons exhibit a strong hysteretic response in field and current, proving the existence of bistable states: droplet and non-droplet states. In the droplet soliton state we find that the magnetization in the contact is almost fully reversed. These observations, in addition to their fundamental interest, are important to understanding and controlling droplet motion, nucleation and annihilation.
具有垂直磁各向异性的磁性薄膜具有局域激发，这些激发对应于反转的、动态进动的磁矩，被称为磁液滴孤子。从根本上说，这些激发与基本自旋激发之间的吸引力相互作用有关，并且在没有阻尼的情况下，已经预测在垂直磁化材料中会发生这种激发。尽管阻尼会抑制这些激发，但当电流在纳米触点中流向铁磁薄膜时，自旋转移扭矩可以补偿这种激发。理论预测，在电流阈值下，纳米触点中会出现磁液滴孤子，最近已经报道了液滴成核的实验特征。然而，迄今为止，这些孤子被观察到是几乎可逆的激发，只有部分反转的磁化。在这里，我们证明了磁液滴孤子在磁场和电流中表现出强烈的滞后响应，证明了双稳态的存在：液滴态和非液滴态。在液滴孤子态中，我们发现接触中的磁化几乎完全反转。这些观察结果除了具有基本意义外，对于理解和控制液滴的运动、成核和湮灭也很重要。
