Optimization of La( Fe, Co)13-xSix based compounds for magnetic refrigeration

The effect of Co on the magnetic, structural and magnetocaloric properties of the LaFe11.7-xCox Si-1.3 (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 -Delta S-max 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, T-C passes from 270 to 294 K and -Delta S-max 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.