Magnetoresistance, specific heat and magnetocaloric effect of equiatomic rare-earth transition-metal magnesium compounds

TL;DR

This study investigates the magnetic, thermal, and electrical properties of equiatomic rare-earth transition-metal magnesium compounds, revealing diverse magnetic behaviors, significant magnetoresistance effects, and notable magnetocaloric responses depending on composition.

Contribution

It provides a comprehensive analysis of the magnetoresistance, specific heat, and magnetocaloric effect in a new class of intermetallic compounds, highlighting their magnetic transitions and potential applications.

Findings

Magnetic order causes a strong decrease in resistivity.

Pronounced magnetoresistance effects are observed near transition temperatures.

Magnetocaloric effect varies with magnetic ordering type, being weak in antiferromagnets and pronounced in ferromagnets.

Abstract

We present a study of the magnetoresistance, the specific heat and the magnetocaloric effect of equiatomic $RET$Mg intermetallics with $RE = {\rm La}$, Eu, Gd, Yb and $T = {\rm Ag}$, Au and of GdAuIn. Depending on the composition these compounds are paramagnetic ($RE = {\rm La}$, Yb) or they order either ferro- or antiferromagnetically with transition temperatures ranging from about 13 to 81 K. All of them are metallic, but the resistivity varies over 3 orders of magnitude. The magnetic order causes a strong decrease of the resistivity and around the ordering temperature we find pronounced magnetoresistance effects. The magnetic ordering also leads to well-defined anomalies in the specific heat. An analysis of the entropy change leads to the conclusions that generally the magnetic transition can be described by an ordering of localized $S=7/2$ moments arising from the half-filled $4f^7$ shells of Eu$^{2+}$ or Gd$^{3+}$. However, for GdAgMg we find clear evidence for two phase transitions indicating that the magnetic ordering sets in partially below about 125 K and is completed via an almost first-order transition at 39 K. The magnetocaloric effect is weak for the antiferromagnets and rather pronounced for the ferromagnets for low magnetic fields around the zero-field Curie temperature.