ABSTRACT
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.
ABSTRACT
The giant magnetocaloric compound Gd5Ge4 is the only member of the Gd5(SixGe1-x)4 family where three-dimensional exchange interactions between two-dimensional correlated layers of the crystallographic structure are so weak that spontaneous ferromagnetism does not set in at any temperature. In this Letter we explore the possibility to reach the ferromagnetic state by application of hydrostatic pressure. Linear thermal expansion and magnetic measurements under pressure reveal that the reduction of the unit cell volume induces a spatially phase-segregated ground state below 10 kbar.
