No abstract

Recently, a so-called “colossal” magnetocaloric effect (MCE) was reported in Mn1−xFexAs [A. de Campos et al., Nat. Mater. 5, 802 (2006)]. However, the value of ΔS that was determined appears markedly overestimated since it results from the inadequate use of the Maxwell relation. Here, we report on recent measurements of ΔS in Mn1−xFexAs from which a correct MCE value is deduced by using the Clausius–Clapeyron equation. This result is asserted by careful use of the Maxwell relation.

The effect of Co on the magnetic, structural and magnetocaloric properties of the LaFe11.7−xCoxSi1.3 (x = 0, 0.3, 0.4, 0.5, 0.6) and LaFe11.2−xCo0.7+xSi1.1 (x = 0, 0.1, 0.2) compounds was investigated by x-ray diffraction and magnetic measurements. For LaFe11.7−xCoxSi1.3 series, the Curie temperature TC increases with increasing Co content. By varying x up to 0.6, the TC of LaFe11.7−xCoxSi1.3 alloys increases from 190 to 265 K and the peak of the isothermal entropy change  −ΔSmax decreases from 28 to 15 J kg−1 K−1 under 5 T. Meanwhile, with Co concentration increasing from 0 to 0.2 in LaFe11.2−xCo0.7+xSi1.1 formula, TC passes from 270 to 294 K and −ΔSmax decreases from 16.5 to 13.5 J kg−1 K−1 under 5 T. Besides, for magnetic refrigeration systems using the Ericsson cycle, the entropy change must remain constant over the refrigeration range. So, we selected some alloys based on LaFe11.7−xCoxSi1.3 (x = 0.4, 0.5, 0.6) and LaFe11.2−xCo0.7+xSi1.1 (x = 0.1 and 0.2) compounds in order to form a composite material working in the 240–300 K temperature range. The optimal mass ratios of the constituents versus magnetic field were calculated. The obtained entropy change of the composite remains approximately constant within the temperature range 240–300 K.

No abstract