Enhanced cryogenic magnetocaloric effect in Eu8Ga16Ge30 clathrate nanocrystals

Abstract

Articles you may be interested inLarge magnetocaloric effects over a wide temperature range in MnCo1−xZnxGe J. Appl. Phys. 113, 17A922 (2013); 10.1063/1.4798339 We observe an enhanced magnetic entropy change (ÀDS M ) at cryogenic temperatures (T < 20 K) in Eu 8 Ga 16 Ge 30 clathrate (type-I) nanocrystals prepared by a ball milling method. With reduction in the crystal size to 15 nm, ÀDS M is enhanced at low temperatures, reaching the highest value ($10 J/kg K) at 5 K for a field change of 5 T. For all samples investigated, there is a cross-over temperature ($25 K) in ÀDS M (T) above which ÀDS M decreases with crystal size, opposite to that observed at low temperatures. A careful analysis of the magnetic and magnetocaloric data reveals that as the crystal size decreases the magnetic interaction between Eu 2þ ions on the Eu2 site governing the primary ferromagnetic transition at $35 K becomes gradually weaker, in effect, altering the interaction between Eu 2þ ions occupying the Eu1 and Eu2 sites responsible for the secondary ferromagnetic transition at 15 K. As a result, we have observed a strong change in magnetization and the enhancement of ÀDS M at low temperature. V C 2015 AIP Publishing LLC.

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“…These results are consistent with a number of publications, e.g. 6,9,10 which show that reducing the size of nanoparticles leads to a shift of the paramagnetic to ferromagnetic phase transition towards lower temperatures and, as a consequence, the maximum of Δ S is also moved towards lower temperatures. It should be also emphasised that the reduction of the dimensionality of the bulk magnetocaloric material to a nanoscale film form can significantly change the magnetic properties of these materials and, consequently, their magnetocaloric properties.…”

Influence of short time milling in R5(Si,Ge)4, R = Gd and Tb, magnetocaloric materials

“…1a) and it is found to be proportional to the milling time. These results are in agreement with other studies like: Gd3Fe5O12 and Eu8Ga16Ge30 clathrate nanocrystals [34,36]. In the case of Tb5Si2Ge2, the XRD pattern remains almost unaltered demonstrating that at room temperature the stable 5:4 phase is the M phase.…”

High Relative Cooling Power in a Multiphase Magnetocaloric FeNiB Alloy

“…First-order transition materials (FOTM) can show good MCE properties, but they exhibit magnetic and temperature hysteresis. In practical applications, which involve magnetic field and temperature cycling, the magnetocaloric materials should exhibit near zero magnetic and thermal hysteresis during an alternating magnetic field and temperature sweeps, respectively [Pecharsky 2006, Biswas 2015. Hysteresis diminishes the energy efficiency of the magnetocaloric device; therefore, secondorder transition materials (SOTM) are generally preferred because of their low hysteresis compared to FOTM.…”