Structural evolution and magnetic properties of L10-type Mn54.5Al45.5-xGax (x = 0.0, 15.0, 25.0, 35.0, 45.5) phase

The intermetallic compounds Mn54.5Al45.5-xGax (x = 0.0, 15.0, 25.0, 35.0, 45.5) with L10 structure were prepared by melt-spinning and annealing. The structural and magnetic properties were investigated by means of X-ray diffraction, neutron powder diffraction and magnetic measurement. Al and Ga atoms are found to occupy both the 1a (0, 0, 0) and 1d (1/2, 1/2, 1/2) sites and show a preference occupation for the 1d site. It was found that the lattice parameter a slightly decreases, while c abnormally increases with the increase of Ga content x, which can be attributed to the fact that the Ga atom located at the 1d sites is larger than that of Al. The mass magnetization decreases from 134 emu/g to 91 emu/g at 5 K as x increases from 0.0 to 45.5 due to higher density of the alloys with Ga in comparison to the alloys with Al. A coercivity (iHc) value of 3.67 kOe and the maximum energy product (BH)max of 2.05 MGOe were obtained for Mn54.5Al30.5Ga15 sample. All the L10 samples show a Curie temperature (Tc) well above room temperature and the value of Tc decreases almost linearly from 644 K for Mn54.5Al45.5 to 578 K for Mn54.5Ga45.5 due to the decrease of ferromagnetic Mn-Mn interaction in the a-b plane. The observed magnetic properties are in accordance with the competing ferromagnetic interactions between Mn moments at the regular 1a site and antiferromagnetic coupling with the excess Mn atoms occupying the Ga (1d) site.