The magnetic and magnetocaloric properties of nanostructured CoMnGe0.95Ga0.05

Evolution of magnetocaloric effect (MCE) of nanostructured CoMnGe0.95Ga0.05 powders has been investigated by electron microscopy (SEM), X-ray powder diffraction (XRD), thermal (DSC) and magnetization measurements. The nanostructured powders are composed of very fine grains (7 +/- 2 and 35 +/- 2 nm) obtained from Rietveld refinements. The nanostructured powders show the unique ferromagnetic martensite-paramagnetic austenite transition around the room temperature like the bulk alloy. Furthermore, while the martensitic transition occurs in narrow temperature for bulk alloy, it occurs in broad temperature range for the nanostructured powders. The isothermal magnetic entropy change values -Delta S-M are estimated from the isothermal magnetization curves. The maximum Delta S-M values of 5 h milled nanopowders are -7.2 and -21.5 J kg(-1) K-1 for a magnetic field change of 2 and 7 T, respectively. The magnitudes of the MCE, magnetic and thermal hysteresis values of nanostructured powders are smaller than those of bulk alloy. Our findings offer the nanostructured CoMnGe0.95Ga0.05 powders for the promising applications in magnetic refrigeration. (C) 2012 Elsevier B. V. All rights reserved.