Abstract
Exchange bias arises from the interfacial exchange coupling in ferromagnet-antiferromagnet bilayers and manifests as a horizontal shift of the magnetic hysteresis loop, constituting a critical component underpinning a broad range of magnetoresistive logic and memory devices. The facile implementation of exchange bias in van der Waals (vdW) magnets would be a key step towards practical devices for emerging vdW spintronics. Here, we report an easy approach to establishing strong exchange bias in the vdW magnet ${\mathrm{Fe}}_{5}\mathrm{Ge}{\mathrm{Te}}_{2}$ by a single-step process---atomic layer deposition (ALD) of oxides on ${\mathrm{Fe}}_{5}{\mathrm{GeTe}}_{2}$. We successfully created exchange bias of 300--1500 Oe in ${\mathrm{Fe}}_{5}\mathrm{Ge}{\mathrm{Te}}_{2}/{\mathrm{Al}}_{2}{\mathrm{O}}_{3}, {\mathrm{Fe}}_{5}\mathrm{Ge}{\mathrm{Te}}_{2}/\mathrm{ZnO}$, and ${\mathrm{Fe}}_{5}\mathrm{Ge}{\mathrm{Te}}_{2}/{\mathrm{V}}_{2}{\mathrm{O}}_{5}$ heterostructures, at 130 K. Control experiments showed that increasing the oxidant pulse duration in each ALD cycle or utilizing the stronger oxidant ${\mathrm{O}}_{3}$ can enhance the exchange bias strength, revealing the key role of the ALD oxidants. Our systematic work elucidates the essential role of ALD-enabled oxidization of ${\mathrm{Fe}}_{5}\mathrm{Ge}{\mathrm{Te}}_{2}$ in the formation of exchange bias, and establishes ALD of oxides as a facile, controllable, and generally effective approach to creating giant exchange bias in vdW magnets, representing an integral advance towards practical vdW spintronic devices.
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