Investigation of Ga substitution in cobalt ferrite (CoGaxFe2-xO4) using Mossbauer spectroscopy

Ga-substituted cobalt ferrite oxides show promise as high magnetostriction, high sensitivity magnetoelastic materials for sensor and actuator applications, but their atomic-level behavior is not yet well understood. In this study, the magnetic environments of the Fe atoms in Ga-substituted cobalt ferrite have been investigated using Mossbauer spectroscopy. A series of five powder samples with CoGaxFe2-xO4 compositions (x=0.0-0.8) was investigated using transmission geometry. Results show two distinct six-line hyperfine patterns, which are identified as Fe in A (tetrahedral) and B (octahedral) spinel sites. Increasing Ga concentration is seen to decrease the hyperfine field strength for both A and B sites, as well as increasing the width of those distributions, consistent with the nonmagnetic nature of Ga3+ ions. Effects are more pronounced for the B sites than the A sites. Results for Ga substitution show more pronounced effects than for previous studies with Cr3+ or Mn3+ substitution: the hyperfine fields decrease and distribution widths increase at greater rates, and the differences between A and B site behavior are more pronounced. Results indicate that at least for the lower Ga concentrations, the Ga3+ ions substitute predominantly into the A sites, in contrast to Cr3+ and Mn3+ which substitute into the B sites. This interpretation is supported by measurements of magnetization at low temperatures. (C) 2008 American Institute of Physics.