Physical Review Applied

Efficient chiral-domain-wall motion driven by spin-orbit torque in metastable platinum films

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The properties and characteristics of thin-film materials strongly depend on their textures and orientations. However, the attainable film morphologies are severely limited by substrates and growth thermodynamics. Metastable films that otherwise cannot be grown by conventional growth methods may overcome these limitations, thus allowing a dramatic expansion of the spectrum of film textures and orientations. Here we present a means to grow metastable platinum layers that are deposited from platinum alloyed with bismuth surfactant material. This is distinct from conventional surfactant-aided growth of films in which surfactants are typically deposited onto the substrate before film deposition, altering the film growth mode but not the film morphology by tuning the surface energy. Surprisingly, we find that almost no bismuth is incorporated into the platinum layer, but rather the structural morphology of this layer is significantly altered. When this metastable platinum layer is applied to spin-orbit-torque technology, a huge increase in the current-driven velocity of chiral domain walls in perpendicularly magnetized wire on top of the metastable platinum layer is observed for otherwise the same current density, while the platinum resistivity is found to barely increase. Our findings show that the metastable film grown from material alloyed with surfactant is promising for the development of devices in various fields, such as spintronics, semiconductors, and quantum materials.