AVS 68 Session MI-WeM: Spin Landscape I (Magnetic Structures in Real and Momentum Space)

Voltage-controlled switching of remnant magnetic states paves the way towards ultra-low power and non-volatile spintronics. In this presentation, I report on a decade-long journey which took us from isothermal electric switching of exchange bias with the help of simultaneously applied electric and magnetic fields to pure voltage-controlled antiferromagnetic spintronics in zero magnetic field and at CMOS compatible temperatures. Nonvolatile Néel vector reorientation in the absence of an applied magnetic field, H, is demonstrated at CMOS compatible temperatures in prototype device structures which exploit the multi-functional properties of thin films of boron (B) doped Cr₂O_3. Boundary magnetization associated with the Néel vector orientation serves as state variable which is read via magnetoresistive detection in a Pt Hall bar adjacent to the B: Cr₂O₃ film. Switching of the Hall voltage between zero and non-zero values implies Néel vector rotation by 90-degrees in agreement with the observed voltage dependent contrast in magnetic force microscopy images. Piezo force microscopy data suggest the presence of polar nanoregions which give rise to uniform polarization in the presence of an applied electric field. The polarization is accompanied piezoelectric straining which, via magnetoelastic coupling, changes the magnetic anisotropy and thus the Néel vector orientation from out of plane to in-plane and back. B-doping enhances the Néel temperature, T_N, of pure chromia. Annealing of the device further increases the T_N-enhancement (up to 500K) at the interface between the Hall bar and the B: Cr₂O₃ surface via thermally activated B-diffusion. The diffusion mechanism is confirmed via cold neutron depth profiling measurements. Robust switching is demonstrated post-annealing for temperature as high as 400K. Theoretical modeling estimates switching speeds of about 100 ps making B: Cr₂O₃ a promising multifunctional single-phase material for energy efficient nonvolatile CMOS compatible memory applications.

We acknowledge financial support by NSF/EPSCoR RII Track-1: Emergent Quantum Materials and Technologies, OIA-2044049. The research was performed in part in the NNF: NNCI and the NCMN, supported by NSF under ECCS:2025208, and the NRI.