Discovery of Griffiths phase in itinerant magnetic semiconductor Fe_{1-x}Co_xS_2

TL;DR

This paper reports the discovery of Griffiths phase behavior in the itinerant magnetic semiconductor Fe_{1-x}Co_xS_2, revealing unusual magnetic and transport properties near a critical doping level.

Contribution

It demonstrates the presence of Griffiths phase-like behavior in a magnetic semiconductor with a percolative magnetic transition.

Findings

Ferromagnetic order appears at x > 0.01

Unusual transport and thermodynamic properties observed near critical doping

Singular behavior indicative of Griffiths phase at zero temperature

Abstract

Critical points that can be suppressed to zero temperature are interesting because quantum fluctuations have been shown to dramatically alter electron gas properties. Here, the metal formed by Co doping the paramagnetic insulator FeS$_2$, Fe$_{1-x}$Co$_x$S$_2$, is demonstrated to order ferromagnetically at $x>x_c=0.01\pm0.005$ where we observe unusual transport, magnetic, and thermodynamic properties. We show that this magnetic semiconductor undergoes a percolative magnetic transition with distinct similarities to the Griffiths phase, including singular behavior at $x_c$ and zero temperature.