Phase transitions in chiral magnets from Monte Carlo simulations

Abstract

Motivated by the unusual temperature dependence of the specific heat in MnSi, comprising a combination of a sharp first-order feature accompanied by a broad hump, we study the extended Heisenberg model with competing exchange $J$ and anisotropic Dzyaloshinskii-Moriya $D$ interactions in a broad range of ratio $D/J$. Utilizing classical Monte Carlo simulations we find an evolution of the temperature dependence of the specific heat and magnetic susceptibility with variation of $D/J$. Combined with an analysis of the Bragg intensity patterns, we clearly demonstrate that the observed puzzling hump in the specific heat of MnSi originates from smearing out of the virtual ferromagnetic second order phase transition by helical fluctuations, which manifest themselves in the transient multiple spiral state. These fluctuations finally condense into the helical ordered phase via a first order phase transition as is indicated by the specific heat peak. Thus the model demonstrates a crossover from a second-order to a first-order transition with increasing $D/J$. Upon further increasing $D/J$ another crossover from a first-order to a second-order transition takes place in the system. Moreover, the results of the calculations clearly indicate that these competing interactions are the primary factor responsible for the appearance of first order phase transitions in helical magnets with the Dzyaloshinskii-Moriya (DM) interaction.

References in corpus (10)

• Multiply periodic states and isolated skyrmions in an anisotropic frustrated magnet
• Skyrmions and Anomalous Hall Effect in a Dzyloshinskii-Moriya Spiral Magnet
• Metallic Quantum Ferromagnets
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• Compact Skyrmions, Merons and Bimerons in Thin Chiral Magnetic Films
• Ultrasonic studies of the magnetic phase transition in MnSi
• Fate of partial order on the trillium and distorted windmill lattices
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• Notes on the Vollhardt "invariant" and phase transition in the helical itinerant magnet MnSi

Cited by in corpus (5)

• Monte Carlo modeling the phase diagram of magnets with the Dzyaloshinskii - Moriya interaction
• Physical properties of (Mn,Co)Si
• Physical properties of MnSi at extreme doping with Co: Quantum criticality
• Spin textures in chiral magnetic monolayers with suppressed nearest-neighbor exchange
• The Vollhardt crossing point at high magnetic field