Field and temperature induced magnetic transition in Gd5Sn4: a giant magnetocaloric material

Viable Materials with a Giant Magnetocaloric Effect

This review of the current state of magnetocalorics is focused on materials exhibiting a giant magnetocaloric response near room temperature. To be economically viable for industrial applications and mass production, materials should have desired useful properties at a reasonable cost and should be safe for humans and the environment during manufacturing, handling, operational use, and after disposal. The discovery of novel materials is followed by a gradual improvement of properties by compositional adjustment and thermal or mechanical treatment. Consequently, with time, good materials become inferior to the best. There are several known classes of inexpensive materials with a giant magnetocaloric effect, and the search continues.

Crystal structure of yttrium gallium antimonide, Y5Ga1.24Sb2.77

Y5Ga1.24Sb2.77, orthorhombic, Pnma (no. 62), a = 7.9629(1) Å, b = 15.175(2) Å, c = 7.9795(1) Å, V = 964.2(2) Å3, Z = 4, R gt(F) = 0.0701, wR ref(F 2) = 0.0741, T = 293 K.

Pressure enhancement of the giant magnetocaloric effect in Tb5Si2Ge2

Effects of temperature and pressure on magnetic, elastic, structural, and thermal properties of Tb5Si2Ge2 have been studied by means of macroscopic (thermal expansion and magnetization) and microscopic (neutron powder diffraction) techniques. We present evidence that the high-temperature second-order ferromagnetic transition can be coupled with the low-temperature first-order structural phase change into a single first-order magnetic-crystallographic transformation at and above a tricritical point in the vicinity of 8.6 kbar. This pressure-induced coupling has a remarkable effect on the magnetocaloric effect, transforming Tb5Si2Ge2 from an ordinary into a giant magnetocaloric effect material.

Massive magnetic-field-induced structural transformation in Gd5Ge4 and the nature of the giant magnetocaloric effect

A massive magnetic-field-induced structural transformation in Gd5Ge4, which occurs below 30 K, was imaged at the atomic level by uniquely coupling high-resolution x-ray powder diffraction with magnetic fields up to 35 kOe. In addition to uncovering the nature of the magnetic field induced structural transition, our data demonstrate that the giant magnetocaloric effect, observed in low magnetic fields, arises from the amplification of a conventional magnetic entropy-driven mechanism by the difference in the entropies of two phases, borne by the concomitant structural transformation.