Physical properties of (Mn,Co)Si

TL;DR

This study investigates the physical properties of Co-doped MnSi, revealing non-Fermi liquid behavior, quantum fluctuations at low temperatures, and the absence of distinct phase transitions at high doping levels.

Contribution

It provides new insights into how impurities affect phase transitions and quantum fluctuations in MnSi, highlighting a gradual transition from classical to quantum behavior.

Findings

All samples show non-Fermi liquid properties.

Impurities eliminate first order phase transition peaks.

Quantum fluctuations dominate at low temperatures.

Abstract

We have grown and characterized three samples of Co doped MnSi and studied their physical properties (magnetization and magnetic susceptibility, heat capacity and electrical resistance). All three samples show non-Fermi liquid physical properties. From literature data and current results follow that impurities (Co and Fe) eliminate the first order phase transition peaks and spread the fluctuation maxima in such a way that its low temperature part effectively reaches the zero temperature, where the fluctuations inevitably become quantum. The behavior of low temperature branches of the heat capacity of the samples suggests that a gradual transition from classical to quantum fluctuations can be described by a simple power function of temperature with the exponent less than one. The $d\rho/dT$ data generally support this suggestion. The values of the heat capacity exponents immediately lead to the diverging ratio $C_p/T$ and hence to the diverging effective electron mass. We found out that at large concentration of the dopant there are no distinct phase transition points. What we observe is a cloud of the helical fluctuations spreading over a significant range of concentrations and temperatures, which become quantum close to 0~K.