Ferromagnetic Insulators


The field of spintronics aims to inject, manipulate and detect spins in electronic devices. Traditionally, spin injection is achieved by passing a spin-neutral current through a ferromagnetic material, thus creating a spin-polarized current which can then be injected into another non-magnetic device channel. The spin state can be controlled by controlling the magnetization direction of the ferromagnetic injection electrode. This spin-polarized electron population can then be used to perform logic operations inside spintronic devices.

Another approach is to take a material which is not ferromagnetic (such as graphene) and selectively induce ferromagnetic ordering by putting it into close proximity to a ferromagnetic insulator (FMI). The overlap of the wavefunctions between the localized magnetic moments in the ferromagnetic insulator and the itinerant electrons in the conduction channel passing near the FMI surface can create an exchange splitting in the non-magnetic channel. Such an approach is advantageous for device applications since it restricts electron transport to the normally non-magnetic channel. This magnetic proximity effect (MPE) is very sensitive so the FMI/non-magnetic film interface quality due to the short range of the exchange interactions. Thus, strict control of the atomic composition as well as cleanliness of the interface are crucial to realizing consistent and tunable MPE.

In our laboratory we can grow multiple high quality FMI thin films (CoFe2O4, EuO, etc.) using molecular beam epitaxy (MBE), a growth technique well known for its cleanliness and ability to engineer precise stoichiometric thin films as thin as a single atomic layer. This allows us to study proximity effects in various heterostructures involving FMIs as well as integrate them into spintronic devices.

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