abstract
- AlFe2B2 and AlFe2-xCoxB2 (x = 0-0.30) were synthesized from the elements in three different ways. The samples were characterized by powder X-ray diffraction, Rietveld refinements, energy-dispersive X-ray spectroscopy, and magnetic measurements. Using Al flux the formation of AlFe2B2 single crystals is preferred. Arc melting enables the substitution of ∼6% Co. This substitution of Fe by Co decreases the Curie temperature TC from 290 to 240 K. The highest Co substitution up to 15% is achieved by spark plasma sintering (SPS). TC is reduced to 205 K. In all cases an excess of Al is necessary to avoid the formation of ferromagnetic FeB. Al13Fe4-xCox is the common byproduct. TC and the cobalt content are linearly correlated. The transition paramagnetic-ferromagnetic remains sharp for all examples. The magnetic entropy change of the Co-containing samples is comparable to AlFe2B2. SPS synthesis yields, in short reaction times, a homogeneous and dense material with small amounts of paramagnetic Al13Fe4-xCox as an impurity, which can serve as sinter additive. These properties make AlFe2-xCoxB2 a promising magnetocaloric material for applications between room temperature and 200 K.