Ahlberg Martina, Chung Sunjae, Jiang Sheng, Frisk Andreas, Khademi Maha, Khymyn Roman, Awad Ahmad A, Le Q Tuan, Mazraati Hamid, Mohseni Majid, Weigand Markus, Bykova Iuliia, Groß Felix, Goering Eberhard, Schütz Gisela, Gräfe Joachim, Åkerman Johan
Department of Physics, University of Gothenburg, 412 96, Gothenburg, Sweden.
Department of Physics Education, Korea National University of Education, Cheongju, 28173, Korea.
Nat Commun. 2022 May 5;13(1):2462. doi: 10.1038/s41467-022-30055-7.
Magnetic droplets are non-topological magnetodynamical solitons displaying a wide range of complex dynamic phenomena with potential for microwave signal generation. Bubbles, on the other hand, are internally static cylindrical magnetic domains, stabilized by external fields and magnetostatic interactions. In its original theory, the droplet was described as an imminently collapsing bubble stabilized by spin transfer torque and, in its zero-frequency limit, as equivalent to a bubble. Without nanoscale lateral confinement, pinning, or an external applied field, such a nanobubble is unstable, and should collapse. Here, we show that we can freeze dynamic droplets into static nanobubbles by decreasing the magnetic field. While the bubble has virtually the same resistance as the droplet, all signs of low-frequency microwave noise disappear. The transition is fully reversible and the bubble can be thawed back into a droplet if the magnetic field is increased under current. Whereas the droplet collapses without a sustaining current, the bubble is highly stable and remains intact for days without external drive. Electrical measurements are complemented by direct observation using scanning transmission x-ray microscopy, which corroborates the analysis and confirms that the bubble is stabilized by pinning.
磁泡是一种非拓扑磁动力学孤子，展现出广泛的复杂动力学现象，具有产生微波信号的潜力。另一方面，磁泡是内部静态的圆柱形磁畴，由外部磁场和静磁相互作用稳定。在其最初的理论中，磁泡被描述为通过自旋转移力矩稳定的即将坍塌的磁泡，在其零频率极限下，等同于一个磁泡。没有纳米级横向限制、钉扎或外部施加磁场时，这样的纳米磁泡是不稳定的，应该会坍塌。在这里，我们表明可以通过降低磁场将动态磁泡冻结成静态纳米磁泡。虽然磁泡的电阻与磁泡几乎相同，但低频微波噪声的所有迹象都消失了。这种转变是完全可逆的，如果在电流下增加磁场，磁泡可以解冻变回磁泡。磁泡在没有持续电流时会坍塌，而磁泡非常稳定，在没有外部驱动的情况下可以保持完整数天。电学测量通过使用扫描透射X射线显微镜的直接观察得到补充，这证实了分析并确认磁泡是通过钉扎稳定的。
