Multi-functional thin films of boron (B) doped Cr2O3 exhibit voltage-controlled and nonvolatile Néel vector reorientation in the absence of an applied magnetic field, H. Toggling of antiferromagnetic states is demonstrated in prototype device structures at CMOS compatible temperatures between 300 and 400 K. The 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. Combined magnetometry, spin resolved inverse photoemission, electric transport and scanning probe microscopy measurements reveal B-dependent TN and resistivity enhancement, spin-canting, anisotropy reduction, dynamic polarization hysteresis and gate voltage dependent orientation of boundary magnetization. The combined effect enables H = 0, voltage controlled, nonvolatile Néel vector rotation at high-temperature. 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.

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When electric and magnetic fields are applied together on a magnetoelectric antiferromagnet, the domain state is subject to reversal. Although the initial and final conditions are saturated singledomain states, the process of reversal may decompose into local multi-domain switching events. In thin films of Cr2O3, the magnetoelectric coercivity and the switching speed found from experiments are considerably lower than expected from magnetic anisotropy, similar to Brown's paradox in ferromagnetic materials. Multi-domain effects originate because antiferromagnetic domain walls are metastably pinned by lattice defects, not due to reduction of magnetostatic energy, which is negligible. This paper theoretically analyzes domain reversal in thin-film magnetoelectric antiferromagnets in the form of nucleation, domain wall propagation, and coherent rotation. The timescales of reversal mechanisms are modeled as a function of applied magnetoelectric pressure. The theory is assessed with reference to latest experimental works on magnetoelectric switching of thin-film Cr2O3: domain wall propagation is found to be dominant and responsible for switching in the experiments. The results bear implications in the energy-delay performance of ME memory devices utilizing antiferromagnetic insulators, which are prospective for nonvolatile technology.

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In this paper, we propose a spin-based true random number generator (TRNG) that uses the inherent stochasticity in nanomagnets as the source of entropy. In contrast to previous works on spin-based TRNGs, we focus on the precessional switching strategy in nanomagnets to generate a truly random sequence. Using the NIST SP 800-22 test suite for randomness, we demonstrate that the output of the proposed TRNG circuit is statistically random with 99% confidence levels. The effects of process and temperature variability on the device are studied and shown to have no effect on the quality of randomness of the device. To benchmark the performance of the TRNG in terms of area, throughput, and power, we use SPICE (Simulation Program with Integrated Circuit Emphasis)-based models of the nanomagnet and combine them with CMOS device models at the 45 nm technology node. The throughput, power, and area footprints of the proposed TRNG are shown to be better than those of existing state-of-the-art TRNGs. We identify the optimal material and geometrical parameters of the nanomagnet to minimize the energy per bit at a given throughput of the TRNG circuit. Our results provide insights into the device-level modifications that can yield significant system-level improvements. Overall, the proposed spin-based TRNG circuit shows significant robustness, reliability, and fidelity and, therefore, has a potential for on-chip implementation.