Chemical potential of magnetic skyrmion quasiparticles in heavy metal/iron bilayers
Physical Review B(2023)
摘要
We performed metadynamics Monte Carlo simulations to obtain the free energy
as a function of the topological charge in the skyrmion-hosting magnetic model
systems (Pt$_{0.95}$Ir$_{0.05}$)/Fe/Pd(111) and Pd/Fe/Ir(111), using a spin
model containing parameters based on ab initio calculations. Using the
topological charge as collective variable, this method allows for evaluating
the temperature dependence of the number of skyrmionic quasiparticles. In
addition, from the free-energy cost of increasing and decreasing the
topological charge of the system we determined chemical potentials as a
function of the temperature. At lower temperature, the chemical potential for
creating skyrmions and antiskyrmions from the topologically trivial state is
different. This splitting of the chemical potential is particularly pronounced
for large external magnetic fields when the system is in a field-polarized
phase. We observed a change in the shape of the free-energy curves when
skyrmion-skyrmion interactions become more pronounced.
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