Strontium Oxide Tunnel Barriers for High Quality Spin Transport and Large Spin Accumulation in Graphene

The quality of the tunnel barrier at the ferromagnet/graphene interface plays a pivotal role in graphene spin valves by circumventing the impedance mismatch problem, decreasing interfacial spin dephasing mechanisms and decreasing spin absorption back into the ferromagnet. It is thus crucial to integrate superior tunnel barriers to enhance spin transport and spin accumulation in graphene. Here, we employ a novel tunnel barrier, strontium oxide (SrO), onto graphene to realize high quality spin transport as evidenced by room-temperature spin relaxation times exceeding a nanosecond in graphene on silicon dioxide substrates. Furthermore, the smooth and pinhole-free SrO tunnel barrier grown by molecular beam epitaxy (MBE), which can withstand large charge injection current densities, allows us to experimentally realize large spin accumulation in graphene at room temperature. This work puts graphene on the path to achieve efficient manipulation of nanomagnet magnetization using spin currents in graphene for logic and memory applications

Room Temperature Intrinsic Ferromagnetism in Epitaxial Manganese Selenide Films in the Monolayer Limit

Monolayer van der Waals (vdW) magnets provide an exciting opportunity for exploring two-dimensional (2D) magnetism for scientific and technological advances, but the intrinsic ferromagnetism has only been observed at low temperatures. Here, we report the observation of room temperature ferromagnetism in manganese selenide (MnSe_<i>x</i>) films grown by molecular beam epitaxy (MBE). Magnetic and structural characterization provides strong evidence that, in the monolayer limit, the ferromagnetism originates from a vdW manganese diselenide (MnSe₂) monolayer, while for thicker films it could originate from a combination of vdW MnSe₂ and/or interfacial magnetism of α-MnSe(111). Magnetization measurements of monolayer MnSe_<i>x</i> films on GaSe and SnSe₂ epilayers show ferromagnetic ordering with a large saturation magnetization of ∼4 Bohr magnetons per Mn, which is consistent with the density functional theory calculations predicting ferromagnetism in monolayer 1T-MnSe₂. Growing MnSe_<i>x</i> films on GaSe up to a high thickness (∼40 nm) produces α-MnSe(111) and an enhanced magnetic moment (∼2×) compared to the monolayer MnSe_<i>x</i> samples. Detailed structural characterization by scanning transmission electron microscopy (STEM), scanning tunneling microscopy (STM), and reflection high energy electron diffraction (RHEED) reveals an abrupt and clean interface between GaSe(0001) and α-MnSe(111). In particular, the structure measured by STEM is consistent with the presence of a MnSe₂ monolayer at the interface. These results hold promise for potential applications in energy efficient information storage and processing