Magnetic behavior of Nd2Fe17xMx (M=Mn, Ga): A comparative study

Samples of Nd2Fe17-xMx, with M = Mn and Ga, were prepared by arc melting and homogenized by annealing at T = 1273 K. Afterwards, specific heat, impedance, X-ray diffraction, Mossbauer spectroscopy, and thermogravimetric measurements were carried out. Results indicate that temperature dependence on impedance changes at transition temperature. Specific heat measurements show an anomaly at transition temperature and this is compared with data reported for Y2Fe17 and Pr2Fe17. Specific heat jump Delta C-p for Nd2Fe17-xMnx as a function of x at transition temperature was obtained from experimental data; this exhibits a decreasing behavior but different from that predicted by the expression derived from the molecular field theory. This disagreement could be attributed to competition between enlarged Fe sublattice and reduction of magnetic moment when Mn is substituted by Fe at preferential sites. On the other hand, substitution with Ga contributes to increasing transition temperature up to T = 552 K for x = 3, as a consequence of enlarged Fe-Fe ion distance producing an increase of ferromagnetic interactions.