Magnetic vortex nucleation/annihilation in artificial-ferrimagnet microdisks

TL;DR

This study investigates temperature-controlled vortex nucleation and annihilation in artificial ferrimagnetic microdisks, revealing hysteresis and metastability due to energy barriers, with potential implications for magnetic memory applications.

Contribution

It demonstrates temperature-induced vortex state transitions in Py/Gd heterostructure microdisks, highlighting the role of energy barriers and metastability in magnetic vortex behavior.

Findings

Vortex nucleation and annihilation occur at different temperatures due to energy barriers.

The magnetization exhibits hysteresis in a narrow temperature range.

Vortices can be metastable at certain temperatures in Py/Gd microdisks.

Abstract

The topological nature of magnetic-vortex state gives rise to peculiar magnetization reversal observed in magnetic microdisks. Interestingly, magnetostatic and exchange energies which drive this reversal can be effectively controlled in artificial ferrimagnet heterostructures composed of rare-earth and transition metals. 25x[Py(t)/Gd(t)] (t=1 or 2 nm) superlattices demonstrate a pronounced change of the magnetization and exchange stiffness in a 10-300 K temperature range as well as very small magnetic anisotropy. Due to these properties, the magnetization of cylindrical microdisks composed of these artificial ferrimagnets can be transformed from the vortex to uniformly-magnetized states in a permanent magnetic field by changing the temperature. We explored the behavior of magnetization in 1.5-micrometer 25x[Py(t)/Gd(t)] (t=1 or 2 nm) disks at different temperatures and magnetic fields and observed that due to the energy barrier separating vortex and uniformly-magnetized states, the vortex nucleation and annihilation occur at different temperatures. This causes the temperature dependences of the Py/Gd disks magnetization to demonstrate unique hysteretic behavior in a narrow temperature range. It was discovered that for the 25x[Py(2 nm)/Gd(2 nm)] microdisks the vortex can be metastable at a certain temperature range.