A nonvolatile memory element for integration with superconducting electronics

We demonstrate a nonvolatile cryogenic magnetic memory element needed to support emerging superconducting- and quantum-computing technologies. The central element is a switchable tri-layer thin film magnetic dot comprising two semiconducting ferromagnetic GdxSm1−xN layers separated by an exchange-blocking Al layer. The materials are explored for their tunable magnetic responses, the potential to engineer compensating magnetic moments in the anti-parallel tri-layers. The stability of the parallel and anti-parallel states and the reproducibility over repeated cycles are also demonstrated. We show that the tri-layer stacks can be formed into dots as small as 4 μm diameter, without affecting their magnetic behavior

Non-volatile memory storage in tri-layer structures using the intrinsically ferromagnetic semiconductors GdN and DyN

We report on the potential use of the intrinsic ferromagnetic rare earth nitride (REN) semiconductors as ferromagnetic electrodes in tunnelling magnetoresistance and giant magnetoresistance device structures for non-volatile memory storage devices. Non-volatile memory elements utilising magnetic materials have been an industry standard for decades. However, the typical metallic ferromagnets and dilute magnetic semiconductors used lack the ability to independently tune the magnetic and electronic properties. In this regard, the rare earth nitride series offer an ultimately tuneable group of materials. Here we have fabricated two tri-layer structures using intrinsically ferromagnetic rare earth nitride semiconductors as the ferromagnetic layers. We have demonstrated both a non-volatile magnetic tunnel junction (MTJ) and an in-plane conduction device using GdN and DyN as the ferromagnetic layers, with a maximum difference in resistive states of ∼1.2% at zero-field. GdN and DyN layers were shown to be sufficiently decoupled and individual magnetic transitions were observed for each ferromagnetic layer

Using optical spectroscopy to probe the impact of atomic disorder on the Heusler alloy Co2MnGa

The exceptional electronic and spintronic properties of magnetic Heusler alloys, which include half-metals and Weyl semimetals, are strongly sensitive to deviations from the ideal atomic structure. To ensure that these materials have been produced with the desired properties, it is necessary to determine both the structural ordering and the electronic structure, which can be challenging. Here, we present the results of a far-infrared-to-visible optical spectroscopy study of films of room-temperature ferromagnetic Weyl semimetal Co2MnGa. Combined with a determination of the level of ordering from x-ray diffraction, we have investigated near Fermi energy valence and conduction band intra- and interband transitions and their dependence on the atomic order. Motivated by band structure calculations, we have modeled our optical spectra with two Drude terms and two Lorentz oscillators, where the latter are assigned to interband transitions. The scattering rate of the itinerant carriers, determined from the width of the Drude term, increases threefold with increasing disorder, while the carrier density to effective mass ratio is unchanged. Based on our band structure and the joint density of states calculations, we have assigned the oscillator that dominates the interband spectral region near 1 eV to transitions across the minority spin gap along the Γ-X direction. It is found that the energy of this transition is strongly sensitive to the degree of order and decreases rapidly with increasing disorder as states fill a decreasing minority spin gap. Our results demonstrate optical spectroscopy is a sensitive way to fingerprint structural order in the technologically relevant near Fermi level electronic states in Heusler alloys