Strong in-plane magnetic anisotropy (Co0.15Fe0.85)5GeTe2/graphene van der Waals heterostructure spin-valve at room temperature

Van der Waals (vdW) magnets are promising owing to their tunable magnetic properties with doping or alloy composition, where the strength of magnetic interactions, their symmetry, and magnetic anisotropy can be tuned according to the desired application. However, most of the vdW magnet based spintronic devices are so far limited to cryogenic temperatures with magnetic anisotropies favouring out-of-plane or canted orientation of the magnetization. Here, we report room-temperature lateral spin-valve devices with strong in-plane magnetic anisotropy of the vdW ferromagnet (Co0.15Fe0.85)5GeTe2 (CFGT) in heterostructures with graphene. Magnetization measurements reveal above room-temperature ferromagnetism in CFGT with a strong in-plane magnetic anisotropy. Density functional theory calculations show that the magnitude of the anisotropy depends on the Co concentration and is caused by the substitution of Co in the outermost Fe layer. Heterostructures consisting of CFGT nanolayers and graphene were used to experimentally realize basic building blocks for spin valve devices such as efficient spin injection and detection. The spin transport and Hanle spin precession measurements prove a strong in-plane and negative spin polarization at the interface with graphene, which is supported by the calculated spin-polarized density of states of CFGT. The in-plane magnetization of CFGT at room temperature proves its usefulness in graphene lateral spin-valve devices, thus opening further opportunities for spintronic technologies

A Room-Temperature Spin-Valve with van der Waals Ferromagnet Fe5GeTe2/Graphene Heterostructure

The discovery of van der Waals (vdW) magnets opened a new paradigm for condensed matter physics and spintronic technologies. However, the operations of active spintronic devices with vdW ferromagnets are limited to cryogenic temperatures, inhibiting their broader practical applications. Here, the robust room-temperature operation of lateral spin-valve devices using the vdW itinerant ferromagnet Fe5GeTe2 in heterostructures with graphene is demonstrated. The room-temperature spintronic properties of Fe5GeTe2 are measured at the interface with graphene with a negative spin polarization. Lateral spin-valve and spin-precession measurements provide unique insights by probing the Fe5GeTe2/graphene interface spintronic properties via spin-dynamics measurements, revealing multidirectional spin polarization. Density functional theory calculations in conjunction with Monte Carlo simulations reveal significantly canted Fe magnetic moments in Fe5GeTe2 along with the presence of negative spin polarization at the Fe5GeTe2/graphene interface. These findings open opportunities for vdW interface design and applications of vdW-magnet-based spintronic devices at ambient temperatures

Photoluminescence and enhanced photocatalytic activity of mechanically activated graphite-zinc oxide composites

In this work, we show evidence of enhanced photocatalytic activity in mechanically activated graphite-zinc oxide (ZnO) composites using time-resolved photoluminescence (TRPL) and time-integrated photoluminescence (TIPL) spectroscopy. The graphite-ZnO composites were synthesized through facile mixing and grinding of graphite and ZnO precursors without any heat treatment. The precursors were ground at room temperature with varying graphite to ZnO mass ratios of 3:1, 2:2, and 1:3 for 0, 2, and 4 h. Raman spectroscopy and x-ray diffractometry confirm the presence of both graphite and ZnO and corroborate the graphite-to-ZnO ratio. XRD results also show a hexagonal wurtzite ZnO crystal structure. To determine the photocatalytic activity of the composites, the degradation of methylene blue (MB) under UV light was measured with a UV–vis spectrophotometer. Nearly full degradation was achieved within a half hour for all composite samples. The kinetic rates of 0.10 min ^−1 were also estimated for mixed and unground samples and samples ground for 2 h. Time-resolved photoluminescence (TRPL) and time-integrated photoluminescence (TIPL) spectroscopy reveal longer lifetimes and more intense UV emissions, respectively, for composite samples compared to pure ZnO. We propose that the even agglomeration of zinc oxide particles on graphite due to grinding enhances the photocatalytic degradation by the zinc oxide. TRPL and TIPL spectroscopy implies the excellent binding between ZnO and graphite, which greatly contributes to the decreased charge recombination resulting in the superior photocatalytic activity observed with our samples