Spin correlations in (Mn,Fe)2(P,Si) magnetocaloric compounds above Curie temperature

X.F Miao,P.C.M Gubbens,H Luetkens,L Caron,P Dalmas De Réotier,N.H Van Dijk,A Yaouanc,E Brück,A Amato

doi:10.1016/j.jsamd.2016.06.002

Abstract

The longitudinal-field muon-spin relaxation (LF-μSR) technique was employed to study the spin correlations in (Mn,Fe)2(P,Si) compounds above the ferromagnetic transition temperature (TC). The (Mn,Fe)2(P,Si) compound under study is found to show itinerant magnetism. The standard deviation of the magnetic field distribution of electronic origin increases with a decrease in temperature, which is attributed to the development of spin correlations. The anomalously low magnetic fluctuation rate is suggested to be another signature of the spin correlations. The development of pronounced magnetic fluctuations is in agreement with the observed deviation of the paramagnetic susceptibility from Curie–Weiss behavior. Our study sheds light on the magneto-elastic transition and the mixed magnetism in (Mn,Fe)2(P,Si) compounds.

Highlights

Magnetic refrigeration, based on the magnetocaloric effect (MCE), has been considered to be the most promising technology to replace vapor-compression for near room temperature refrigeration applications [1e6]
According to the Rhodes-Wohlfarth model [47,48], this indicates itinerant magnetism for the (Mn,Fe)2(P,Si) compounds, which is in agreement with previous studies on the Fe2P parent compound [33,45,49,50]
The itinerant magnetism in the Fe2P-based compounds reflects the instability of the Fe moment on the 3f site

Summary

Introduction

Magnetic refrigeration, based on the magnetocaloric effect (MCE), has been considered to be the most promising technology to replace vapor-compression for near room temperature refrigeration applications (e.g. refrigerator, air-conditioner) [1e6]. Among the diverse classes of magnetocaloric materials, the (Mn,Fe)2(P,Si)-based [21e25] compounds have been considered as the most promising materials for near roomtemperature refrigeration and energy conversion applications due to their combination of a giant MCE, a tunable working temperature, low hysteresis and low material cost. (Mn,Fe)2(P,Si) compounds crystallize in a hexagonal Fe2P-type structure (space group P-62m), which contains two metallic (3f and 3g) and two non-metallic (2c and 1b) sites. The time dependence of muon-spin polarization can be reconstructed by collecting the emitted positrons, which in turn reflects the static and dynamic properties of the local magnetic field. This study provides new insight into the mixed magnetism and the magneto-elastic phase transition in the (Mn,Fe)2(P,Si) compounds

Experimental

Magnetization measurement

Conclusions