Ariana de Campos

The magnetic and magnetocaloric properties of Gd5Ge2Si2 compound under hydrostatic pressure

The Gd5Ge2Si2 compound presents a giant magnetocaloric effect with transition temperature at around 276 K and is a very good candidate for application as an active regenerator material in room temperature magnetic refrigerators. Recently it has been shown that pressure induces a colossal magnetocaloric effect in MnAs, a material that presents a giant magnetocaloric effect and a strong magnetoelastic coupling, as also happens with the Gd5Ge2Si2 compound. This motivated a search of the colossal effect in the Gd5Ge2Si2 compound. This work reports our measurements on the magnetic properties and the magnetocaloric effect of Gd5Ge2Si2 under hydrostatic pressures up to 9.2 kbar and as a function of temperature. Contrary to what happens with MnAs, pressure increases the Curie temperature of the compound, does not affect the saturation magnetization and decreases markedly its magnetocaloric effect.

Ambient pressure colossal magnetocaloric effect in Mn1−xCuxAs compounds

Magnetic refrigeration is a good alternative to gas compression technology due to higher efficiency and environmental concerns. Magnetocaloric materials must exhibit large adiabatic temperature variations and a large entropic effect. MnAs shows the colossal magnetocaloric effect under high pressures or with Fe doping. In this work the authors introduce a class of materials—Mn1−xCuxAs—revealing a peak colossal effect of −175J∕(Kkg) for a 5T field variation at 318K and ambient pressure.

Structural and magnetic study of the MnAs magnetocaloric compound

The temperature induced phase transition in MnAs is analyzed in this work using X ray Rietveld refinement. The results show the presence of the hexagonal phase (P63/mmc) at room temperature and the first-order structural-magnetic transition to the orthorhombic phase (Pnma) around 318 K was followed in detail. The MnAs magnetic characterization allowed to obtain the transition temperature and a maximum value of 47 J/(kg.K) for the measured magnetocaloric effect for a magnetic field variation of 5 T.

History dependence of directly observed magnetocaloric effects in (Mn, Fe)As

We use a calorimetric technique operating in sweeping magnetic field to study the thermomagnetic history-dependence of the magnetocaloric effect (MCE) in Mn0.985Fe0.015As. We study the magnetization history for which a “colossal” MCE has been reported when inferred indirectly via a Maxwell relation. We observe no colossal effect in the direct calorimetric measurement. We further examine the impact of mixed-phase state on the MCE and show that the first order contribution scales linearly with the phase fraction. This validates various phase-fraction based methods developed to remove the colossal peak anomaly from Maxwell-based estimates.

Synthesis of SnSb2Te4 Microplatelets by High-energy Ball Milling

In this work we demonstrate that high-energy ball milling process can be used to synthesize SnSb2Te4 without surfactant and further annealing. Milling parameters such as ball to raw material ratio (5:1) and milling time (2h) were determined to be suitable for synthesizing microplatelets of SnSb2Te4. The powders after milling for various durations were characterized by X-ray powder diffraction, scanning electron microscopy and electrical resistance measurements.