Reduction of energy cost of magnetization switching in a biaxial nanoparticle by use of internal dynamics

A solution to energy-efficient magnetization switching in a nanoparticle with biaxial anisotropy is presented. Optimal control paths minimizing the energy cost of magnetization reversal are calculated numerically as functions of the switching time and materials properties, and used to derive energy-efficient switching pulses of external magnetic field. Hard-axis anisotropy reduces the minimum energy cost of magnetization switching due to the internal torque in the desired switching direction. Analytical estimates quantifying this effect are obtained based on the perturbation theory. The optimal switching time providing a tradeoff between fast switching and energy efficiency is obtained. The energy cost of switching and the energy barrier between the stable states can be controlled independently in a biaxial nanomagnet. This provides a solution to the dilemma between energy-efficient writability and good thermal stability of magnetic memory elements.Comment: 13 pages, 10 figure

Crystalline Field Effects on Magnetic and Thermodynamic properties of a Ferrimagnetic Centered Rectangular Structure

The magnetic properties and phase diagrams of the mixed spin Ising model, with spins S=1 and {\sigma}=1/2 on a centered rectangular structure, have been investigated using Monte Carlo simulations based on the Metropolis algorithm. Every spin at one lattice site has four nearest-neighbor spins of the same type and four of the other type. We have assumed ferromagnetic interaction between the same spins type, antiferromagnetic for different spin types. An additional single-site crystal field term on the S=1 site was considered. We have shown that the crystal field enhances the existence of the compensation behavior of the system. In addition, the effects of the crystal field and exchange coupling on the magnetic properties and phase diagrams of the system have been studied. Finally, the magnetic hysteresis cycles of the system for several values of the crystal field have been found.Comment: 19 pages, 12 figures. arXiv admin note: text overlap with arXiv:2012.1092

Optimal Control of Magnetization Reversal in a Monodomain Particle by Means of Applied Magnetic Field

A complete analytical solution to the optimal reversal of a macrospin with easy-axis anisotropy is presented. Optimal control path minimizing the energy cost of the reversal is identified and used to derive time-dependent direction and amplitude of the optimal switching field. The minimum energy cost of the reversal scales inversely with the switching time for fast switching, follows an exponential asymptotics for slow switching and reaches the lower limit proportional to the energy barrier between the target states and to the damping parameter at infinitely long switching time. For a given switching time, the energy cost is never smaller than that for a free macrospin. This limitation can be bypassed by adding a hard anisotropy axis which activates the internal torque in the desired switching direction, thereby significantly reducing the energy cost. Comparison between the calculated optimal control path and minimum energy path reveals that optimal control does not translate to the minimization of the energy barrier, but signifies effective use of the system's internal dynamics to aid the desired magnetic transition