Microstructural Changes and Hysteresis Losses in Fe-Doped GdSiGe

Abstract

Magnetocaloric Gd 5 Si 2 Ge 2 -based alloys exhibit a well-documented giant magnetocaloric effect at around room temperature. However, as candidate materials for real-world refrigeration devices, they suffer from a number of problems, one of which is large hysteresis losses while cycling in and out of the magnetic field. It has, however, been reported that a small amount of iron reduces these hysteresis losses very significantly, so increasing the total potential cooling capacity of the material. We have investigated the magnetic properties as well as the macro-and microstructural changes for a wide range of iron substitutions for silicon, according to the formula Gd 5 Si 2 x Fe x Ge 2 , where x was varied between 0 and 1. The samples were prepared with an arc-melter and homogenized in an inert atmosphere, after which they were analyzed with a nano-resolution field-emission-gun scanning electron microscope (FEG SEM) and an X-ray diffractometer. The magnetic measurements were made with a cryogenic vibrating-sample magnetometer. The substitution of silicon for iron presented us with some unusual macrostructures and a consistent change in the microstructures of the samples. While most of the iron forms part of the grain-boundary phases, it also results in the formation of a new Gd 5 (SiGe) 3 main phase. We also observed that the addition of iron lowered the Curie temperature of the alloy, but only had a minimal effect on reducing the hysteresis losses, suggesting that this previously observed reduction in the hysteresis losses only occurs with very small substitutions of iron.Index Terms-Gd 5 Si 2 Ge 2 -type alloys, magnetic hysteresis, magnetocaloric effect, microstructure.

R5T4 Compounds

“…The Curie temperatures of the Ga-substituted alloys correspond to the second-order transition of the O(I) phase ($299 K). The substitution of Si by Fe, however, does not suppress the structural transition in Gd 5 Si 2Àx Fe x Ge 2 alloys but instead promotes the formation of the 5:3 phase (Podmiljšak et al, 2008(Podmiljšak et al, , 2009a. Magnetocaloric properties of the Gd 5 Si 2 Ge 1.9 Ga 0.1 sample, which according to the X-ray powder diffraction analysis contained $81% of the 5:4 major phase, $4% of the 1:1 phase, and $15% of the 5:3 phase, were studied by means of heat capacity and direct magnetocaloric measurements (Palacios et al, 2010a).…”

Hcp cobalt nanocrystals with high magnetic anisotropy prepared by easy one-pot synthesis

“…3a In magnetism, 4 a wide range of applications can be found starting from the storage of information 4a to nanoelectronics and spintronics 4d and also magnetocaloric materials, designing new alloys allowing cooling. 5 Among these materials cobalt NCs are of particular interest due to their unique magnetic properties. Indeed cobalt NCs exist in three crystalline forms, hcp (hexagonal close-packed), fcc (facecentered cubic) and ε-cobalt; the first one being the most interesting in terms of magnetic properties due to its high magnetocrystalline anisotropy.…”

A Contrastive Analysis of Gd5(SixGe1-x) Based Alloys Useful for Magnetic Refrigeration

“…Though most investigation were made for Ge substitution, a significant reduction in Δ|S M | because of the suppression of the structural transformation has been observed so it is suggested that Si and Ge should be substituted simultaneously for Fe and Sn doping as can be seen in Table 3 [15,[28][29][30][31]. A small substitution with iron (substituting for 5% of the germanium, otherwise it will have deleterious effect on MCE properties and minimal effect on reducing hysteresis losses [28,30]) reduced the losses by 90% thus resulting in 20%-50% higher RCP value, though it overall reduced the Δ|S M | to only one-third of its original value [27,29,30]. The T C of the matrix phase cess.…”