Spin Glass ground state in Mn$_{1-x}$Co$_{x}$Si

TL;DR

This study uncovers a new spin glass ground state in Mn$_{1-x}$Co$_{x}$Si, revealing complex magnetic phase behavior and the persistence of helimagnetic order up to certain Co concentrations.

Contribution

It demonstrates the existence of a spin glass phase in Mn$_{1-x}$Co$_{x}$Si and details the evolution of magnetic order with Co doping, including the suppression of helimagnetism.

Findings

Helimagnetic order persists up to x=0.05

Spin glass state appears for 0.05<x<0.90

Resistivity minimum linked to magnetic scattering

Abstract

We report the discovery of a new spin glass ground state in the transition metal monosilicides with the B20 crystallographic structure. Magnetic, transport, neutron and muon investigation of the solid solution Mn$_{1-x}$Co$_{x}$Si have revealed a new dome in the phase diagram with evidence of antiferromagnetic interactions. For Mn rich compounds, a sharp decrease of the Curie temperature is observed upon Co doping and neutron elastic scattering shows that helimagnetic order of MnSi persists up to $x=0.05$ with a shortening of the helix period. For higher Co ($0.05<x<0.90$) concentrations, the Curie-Weiss temperature changes sign and the system enters a spin glass state upon cooling ($T_g=9$ K for $x_{Co}=0.50$), due to chemical disorder. In this doping range, a minimum appears in the resistivity, attributed to scattering of conduction electron by localized magnetic moments.