Crystal Structure and Magnetic Properties of ϵ-Ru_x Fe_2-x O₃ Nanosize Hard Ferrite

A new series of metal-substituted ϵ-iron oxides, ϵ-Ru_x Fe_2-x O₃ (x=0 (1), 0.005 (2), and 0.014 (3)) nanoparticles (average size=20 nm) is synthesized by sintering iron oxide hydroxide with ruthenium hydroxide in a silica matrix. The samples are characterized by inductively coupled plasma mass spectrometry, and energy dispersive X-ray spectroscopy (EDS) of transmission electron microscope. The X-ray diffraction pattern shows that ϵ-Ru_x Fe_2-x O₃ has an orthorhombic crystal structure with a space group of Pna2₁ and the Rietveld analyses show that Ru is doped selectively at the regular octahedral C site among the four non-equivalent Fe sites (A, B, C, and D site). Magnetization vs. temperature plots show that the Curie temperature (T_C ) depends on x, and T_C =498 K for 1, 497 K for 2, and 496 K for 3. Magnetization vs. external magnetic field plots indicate that the coercive field (H_c ) increases from 17.7 kOe (1) to 20.3 kOe (3). This increment of 15 % on H_c is attributed to the single ion anisotropy of the magnetic spin on Ru^III (4d⁵ , S=1/2).