Multiple magnetic transition and magnetocaloric properties in the mixed valence Eu8CuNi2.5Si42.5 type I clathrate compound

TL;DR

This paper explores the magnetic and cooling properties of a new compound, finding it could be useful for low-temperature cooling applications.

Contribution

The study reveals multiple magnetic transitions and high refrigerant capacity in a mixed-valence Eu-based clathrate compound.

Findings

Eu8CuNi2.5Si42.5 shows multiple magnetic transitions from ferromagnetic to antiferromagnetic states.

The compound exhibits a high spin entropy change over a broad temperature range.

Spontaneous magnetization and spin reorientation are observed under varying magnetic fields.

Abstract

We investigated the magnetocaloric and electrical transport properties of the Eu8CuNi2.5Si42.5 clathrate compound, synthesized by an arc melting and annealing method. X-ray photoemission spectroscopy revealed a mixed valence state of Eu2+ and Eu3+. The low-field and low-temperature magnetic measurements indicated a multiple magnetic transition, from ferromagnetic near 35 K to antiferromagnetic at 25 K. Increasing the magnetic field led to the broadening of antiferromagnetic peaks and a final ferromagnetic state under high magnetic fields, indicative of spin reorientation. The transition from a ferromagnetic to an antiferromagnetic state was further corroborated by specific heat measurements. We noted spontaneous magnetization at low temperatures via magnetic hysteresis and Arrott plot analysis. The coexistence of an antiferromagnetic ground state (attributed to the Eu2+ ions) and ferromagnetic clusters (associated with the Ni2+ ions) was supported by spontaneous magnetization at low temperatures in the antiferromagnetic state. The magnetocaloric analyses revealed a high spin entropy change over a broad temperature range for Eu8CuNi2.5Si42.5, which implies its potential as a robust low-temperature magnetocaloric material, distinguished by its high refrigerant capacity.

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