Crystal Structure and Magnetic Properties of ϵ ‐Ru x Fe 2‐ x O 3 Nanosize Hard Ferrite

A new series of metal‐substituted ϵ ‐iron oxides, ϵ ‐Ru x Fe 2‐ x O 3 ( 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 O 3 has an orthorhombic crystal structure with a space group of Pna 2 1 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 ( 4 d 5 , S =1/2).