5 Mar 2006 | U.K. Rößler and A.N. Bogdanov*, C. Pfleiderer
The paper discusses the spontaneous formation of skyrmion ground states in magnetic metals, challenging the conventional belief that skyrmions cannot form spontaneous ground states like ferromagnetic or antiferromagnetic order. The authors present a phenomenological continuum model based on material-specific parameters to demonstrate that skyrmion textures can spontaneously form in condensed matter systems with chiral interactions, without the need for external fields or topological defects. They show that this is possible in a wide range of materials, particularly at surfaces and in thin films, where a lack of space inversion symmetry leads to chiral interactions. The model considers a hierarchy of energy and length scales, with ferromagnetic exchange favoring spin alignment, chiral interactions favoring spin rotations, and magnetic anisotropies and dipolar interactions determining the direction of spins. The authors analyze the stability of cylindrical skyrmions and predict that they can form spontaneously within a finite temperature interval, leading to a phase diagram with a skyrmion phase and a helix phase. They also discuss the potential experimental verification of these predictions using techniques such as polarized magnetic neutron scattering and real-space imaging. The study is inspired by recent high-pressure experiments in MnSi, where the spontaneous formation of an amorphous magnetic state was observed, providing a simple explanation for the observed resistivity behavior.The paper discusses the spontaneous formation of skyrmion ground states in magnetic metals, challenging the conventional belief that skyrmions cannot form spontaneous ground states like ferromagnetic or antiferromagnetic order. The authors present a phenomenological continuum model based on material-specific parameters to demonstrate that skyrmion textures can spontaneously form in condensed matter systems with chiral interactions, without the need for external fields or topological defects. They show that this is possible in a wide range of materials, particularly at surfaces and in thin films, where a lack of space inversion symmetry leads to chiral interactions. The model considers a hierarchy of energy and length scales, with ferromagnetic exchange favoring spin alignment, chiral interactions favoring spin rotations, and magnetic anisotropies and dipolar interactions determining the direction of spins. The authors analyze the stability of cylindrical skyrmions and predict that they can form spontaneously within a finite temperature interval, leading to a phase diagram with a skyrmion phase and a helix phase. They also discuss the potential experimental verification of these predictions using techniques such as polarized magnetic neutron scattering and real-space imaging. The study is inspired by recent high-pressure experiments in MnSi, where the spontaneous formation of an amorphous magnetic state was observed, providing a simple explanation for the observed resistivity behavior.