Exploring supermagnetism in patterned thin films of La0.7Sr0.3MnO3
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Supermagnetism refers to the collective magnetic ordering of superparamagnetic nanoparticles. The phenomenon may be used to engineer novel magnetic materials. To investigate how supermagnetism may be manifest in patterned thin films of the ferromagnetic complex oxide La0.7Sr0.3MnO3 (LSMO), we used GPU-accelerated micromagnetic simulations to investigate the magnetic properties of single LSMO nanomagnets and ordered arrays of such nanomagnets. We found superparamagnetism in 5nm thick, cylindrical LSMO nanomagnets at diameters of 20 nm to 140 nm. We then investigated the supermagnetic ground states of ordered arrays of LSMO nanomagnets, and found that by controlling the stacking of the arrays, the supermagnetic ground state could be tuned. Square stacking lead to superantiferromagnetic ground states and hexagonal stacking to superferromag- netic ground states. Effects of finite size and tuning the ground state by an applied field were discussed. We explored the hysteretic properties of the arrays, and found a step-like hysteresis curve for the square lattice. It was explained in terms of dipolar lattices and supermagnetic phase transitions, and compared with 2D Ising spin-lattices. The hexagonal array exhibited hysteresis similar to that of conventional soft magnetic materials. Spin-glass properties of the arrays were explored by looking at quenched disorder, and field-cooled and zero-field cooled magnetization of the arrays. Magnetic irreversibility was found, which was suggestive of spin-glass behavior. We conclude that ordered supermagnetic systems are excellent candidates for engineering artifical spin systems and magnetic metamaterials, either for technological or fundamental research purposes, and that such systems can be realized in patterned LSMO thin films.