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Direct Observation of Zhang-Li Torque Expansion of Magnetic Droplet Solitons

Journal article
Authors Sunjae Chung
Q. Tuan Le
Martina Ahlberg
Ahmad Awad
Markus Weigand
Iuliia Bykova
Roman Khymyn
Mykola Dvornik
Hamid Mazraati
Afshin Houshang
Sheng Jiang
Thoai N. Anh Nguyen
Eberhard Goering
Gisela Schütz
Joachim Gräfe
Johan Åkerman
Published in Physical Review Letters
Volume 120
Issue 21
ISSN 0031-9007
Publication year 2018
Published at Department of Physics (GU)
Language en
Subject categories Condensed Matter Physics


Magnetic droplets are nontopological dynamical solitons that can be nucleated in nanocontact based spin torque nano-oscillators (STNOs) with perpendicular magnetic anisotropy free layers. While theory predicts that the droplet should be of the same size as the nanocontact, its inherent drift instability has thwarted attempts at observing it directly using microscopy techniques. Here, we demonstrate highly stable magnetic droplets in all-perpendicular STNOs and present the first detailed droplet images using scanning transmission X-ray microscopy. In contrast to theoretical predictions, we find that the droplet diameter is about twice as large as the nanocontact. By extending the original droplet theory to properly account for the lateral current spread underneath the nanocontact, we show that the large discrepancy primarily arises from current-in-plane Zhang-Li torque adding an outward pressure on the droplet perimeter. Electrical measurements on droplets nucleated using a reversed current in the antiparallel state corroborate this picture.

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