Anomalous magnetoentropic response of skrymion crystals

Abstract

We investigate theoretically magnetoentropic signatures of the crystal phase of magnetic skyrmions of various kinds, commonly appearing in two dimensions, \textit{viz.}, Néel, Bloch and anti skyrmions. Using Monte Carlo calculations based on spin Hamiltonians, we obtain magnetic entropy change $\Delta S_m$ in the presence of three different types of Dzyaloshinskii-Moriya interactions responsible for these skyrmions. The phase mapping of $\Delta S_m$ using skyrmion counting number $N_{sk}$ in temperature-magnetic field plane reveals fluctuation-dominated weak first-order transition in the precursor phase of the skyrmions, and a sign change in $\Delta S_m$ when the system enters into the skyrmion crystal phase -- in agreement with recent experimental findings. We also find that the fractional entropy change in going from a ferromagnetic phase to the skyrmion crystal phase is much larger compared to the conventional route of paramagnetic phase to ferromagnetic phase, used for the purpose of magnetic cooling. The magnetoentropic signatures of the different types of skyrmion crystals are found to be similar. Our results indicate that the skyrmion crystals exhibit enhanced cooling efficiency and have the potential to upgrade the existing magnetic cooling methods.

8 pages, 5 figures

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