Robust metastable skyrmions with tunable size in the chiral magnet FePtMo$_3$N

TL;DR

This study introduces FePtMo$_3$N as a new chiral magnet hosting robust, tunable-size skyrmions, demonstrating their stability and controllability, which are promising for future topological magnetic applications.

Contribution

The paper reports the discovery of metastable skyrmions in FePtMo$_3$N with tunable sizes and demonstrates their robustness and zero-field stability, advancing the understanding of skyrmion control in chiral magnets.

Findings

Skyrmions in FePtMo$_3$N are stable against field cooling at low temperatures.

Skyrmion size can be continuously tuned between 120 and 210 nm by temperature.

Skyrmion lattice persists even in zero magnetic field after field cooling.

Abstract

Synthesis of new materials that can host magnetic skyrmions and their thorough experimental and theoretical characterization are essential for future technological applications. The $\beta$-Mn-type compound FePtMo$_3$N is one such novel material that belongs to the chiral space group $P4_132$, where the antisymmetric Dzyaloshinkii-Moriya interaction is allowed due to the absence of inversion symmetry. We report the results of small-angle neutron scattering (SANS) measurements of FePtMo$_3$N and demonstrate that its magnetic ground state is a long-period spin helix with a Curie temperature of 222~K. The magnetic field-induced redistribution of the SANS intensity showed that the helical structure transforms to a lattice of skyrmions at $\sim$13~mT at temperatures just below $T_{\text C}$. Our key observation is that the skyrmion state in FePtMo$_3$N is robust against field cooling down to the lowest temperatures. Moreover, once the metastable state is prepared by field cooling, the skyrmion lattice exists even in zero field. Furthermore, we show that the skyrmion size in FePtMo$_3$N exhibits high sensitivity to the sample temperature and can be continuously tuned between 120 and 210~nm. This offers new prospects in the control of topological properties of chiral magnets.