Specific Features of Magnetic Phase Diagram of an MnSi Helimagnet

TL;DR

This study investigates the magnetic phase diagram of MnSi, revealing new features near the transition temperature and clarifying the nature of the intermediate magnetic states through detailed magnetization measurements.

Contribution

It provides detailed magnetic phase diagrams of MnSi near the transition temperature, identifying anomalies linked to the conical phase and differentiating it from the A phase.

Findings

Anomalies in $dM/dH$ curves above $T_N$ indicate complex magnetic behavior.

The characteristic field $H^*(T)$ extrapolates the transition from conical to ferromagnetic phases.

Properties in the intermediate region are governed by the conical phase, not the A phase.

Abstract

Magnetization curves of MnSi single crystals have been measured in a range of temperatures $T = 5.5 - 35$ K and magnetic field strengths $H \leq 11$ kOe for $H \parallel$ [111], [001], and [110]. Special attention has been paid to the temperature interval near $T_N = 28.8$K, where MnSi exhibits a transition to the state with a long-period helical magnetic structure. Some new features in the magnetic behavior of MnSi have been found. In particular, in an intermediate temperature region above the transition (28.8 K $= T_N \leq T < 31.5$ K), the $dM(H)/dH$ curves exhibit anomalies that are not characteristic of the typical paramagnetic state. It is established that the line of the characteristic field $H^ \ast (T)$ of this anomaly is a natural extrapolation of the temperature dependence of the field of the transition from a conical phase to an induced ferromagnetic phase observed at $T < T_N$. It is concluded that the properties of MnSi in the indicated intermediate region are related to and governed by those of the conical phase (rather than of the A phase). Based on these data, magnetic phase diagrams of MnSi for $H \parallel$ [111], [001], and [110] are plotted and compared to diagrams obtained earlier by other methods.