Effects of Boron diffusion on the surface Néel temperature revealed by magnetotransport and cold neutron depth profiling in B-doped Cr₂O₃ films

Multi-functional thin films of boron (B) doped Cr₂O₃ grown by pulsed laser deposition exhibit voltage-controlled and nonvolatile Néel vector reorientation in the absence of a magnetic field. Isothermal toggling of antiferromagnetic states is demonstrated in prototype device structures at CMOS compatible temperatures between 300 and 400 K. Although isothermal switching is achieved, selecting a single domain state via a magnetoelectric annealing protocol is hampered most likely by a thermally activated runaway effect of the Néel temperature. This behavior can be understood by considering B diffusion within the thin Cr₂O₃ film. Cold Neutron Depth Profiling (cNDP), performed at National Institute of Standards and Technology, points at progressing depletion of B atoms in the bulk with temperature. At the same time the B-concentration increases near the surface. The Spin Hall measurements, sensitive to the surface magnetic state, indicate a shift in T_N towards higher values associated with the increase in B-concentration near the film surface.