Critical dependence of magnetostructural coupling and magnetocaloric effect on particle size in Mn-Fe-Ni-Ge compounds

Abstract

Magnetostructural coupling, which is the coincidence of crystallographic and magnetic transition, has obtained intense attention for its abundant magnetoresponse effects and promising technological applications, such as solid-state refrigeration, magnetic actuators and sensors. The hexagonal Ni2In-type compounds have attracted much attraction due to the strong magnetostructural coupling and the resulted giant negative thermal expansion and magnetocaloric effect. However, the as-prepared samples are quite brittle and naturally collapse into powders. Here, we report the effect of particle size on the magnetostructural coupling and magnetocaloric effect in the Ni2In-type Mn-Fe-Ni-Ge compound, which undergoes a large lattice change across the transformation from paramagnetic austenite to ferromagnetic martensite. The disappearance of martensitic transformation in a large amount of austenitic phase with reducing particle size, to our best knowledge, has not been reported up to now. The ratio can be as high as 40.6% when the MnNi0.8Fe0.2Ge bulk was broken into particles in the size range of 5~15 μm. Meanwhile, the remained magnetostructural transition gets wider and the magnetic hysteresis becomes smaller. As a result, the entropy change drops, but the effective cooling power RCeffe increases and attains to the maximum at particles in the range of 20~40 μm. These observations provide constructive information and highly benefit practical applications for this class of novel magnetoresponse materials.

Enhanced magnetocaloric effect in Ni-Mn-Sn-Co alloys with two successive magnetostructural transformations

“…8. Noteworthily, the RC eff of the present Co6 alloy reaches 223 J/kg, which is significantly larger than those of the stoichiometric Ni-Mn-based alloys 18,45,76,77,79,81–84 and is comparable to those of some Co-doped Mn-rich Ni-Mn-based compounds 1,63,78–80,83 . Besides, the achieved RC eff is also comparable to those rare-earth containing La(FeSi) 13 -based 72,73 and Gd 5 (SiGe) 4 -based 74,75 compounds.…”

Negative Thermal Expansion in the Materials With Giant Magnetocaloric Effect

“…The introduced residual strain and defects during pulverization (Wu et al, 2016) or cold pressing (Liu et al, 2015) can also affect the magnetostructural coupling besides hydrostatic pressure. It has been reported that the introduced residual strain in the MnCoGe 1−x In x thin slices prepared by cold pressing can stabilize the austenite phase, as a result, the temperature window of martensitic transformation is broadened, the magnetic and structural transition becomes decoupling (Liu et al, 2015).…”

Magnetocaloric Properties of Fe-Ni-Cr Nanoparticles for Active Cooling

“…First order transition materials (FOTM) which exhibit simultaneous magnetic and structural transition result in high isothermal entropy change242526. However, the narrow working temperature span and large magnetic and thermal hysteresis in FOTM limit real-world applications5132728.…”