Structural and magnetic properties of 2:17-type rare-earth transition-metal magnetic compounds samarium(2)iron(17)M(x) (M = aluminum, silicon) and R(2)iron(17-x)T(x) (R = yttrium, neodymium, gadolinium T = indium, cobalt, silicon, gallium).

摘要

Our aim is to develop new RE-TM intermetallic compounds of the 2:17-type that have high Curie temperature Tc, large saturation magnetization Ms, and strong magnetocrystalline anisotropy (MCA). The new off-stoichiometric compound Sm2Fe17ALx formed the rhombohedral Th2Zn17-type structure when x was less than 6. The addition of Al increased its Tc due to the change of distance between the Fe-Fe pairs that were responsible for the exchange coupling. When Co, or Ni was used to substitute the Fe atoms in Sm2Fe17Al x, the substitution further enhanced Tc whereas Ms increased first and then decreased. A differential thermal analysis was made on the carbides of these samples, the results showed that Sm2Fe 16MnAl2C1.5 was stable even near 950°C. In the second part of the work, the effects of Co substitution on the exchange coupling and the magnetocrystalline anisotropy (MCA) of Sm2Fe 17-xCox were studied. The result was explained by the Mean Field Theory and the Sucksmith Model. It was found that the MCA constant K1 and the coupling constant JFe-Fe increased monotonously with Co concentration which indicated the weakening of the easy axis anisotropy. This result was consistent with the observed fact that the easy magnetization direction did not change with Co concentration as verified by the x-ray diffraction spectra of the aligned samples. Lastly, the electronic structure of the 2:17-type RE-TM compounds were studied by using x-ray photoelectron spectroscopy. An increment of density of state near the Fermi energy level (EF) had been observed on the Y2Fe17-xInx and Nd2Fe17-xMx (M = Ga, Si) compound as the substitution concentration increased, but it was not found in the Gd 2Fe17-xTx (T = Ga, Ti x = 2). The XPS of the valence band of the Y2Fe17-xInx exhibited a one-peak structure, whereas those of the Nd2Fe 17-xTx and Gd2Fe17-xT x had a two-peak structure. It was evident that the formation of the two-peak structure was due to the presence of the 4f electrons, because the 4f electrons were not found in the Y atom.