Gallium substituted “114” YBaFe4O7: from a ferrimagnetic cluster glass to a cationic disordered spin glass

Abstract

The study of the ferrites YBaFe_4-xGa_xO₇ shows that the substitution of Ga for Fe in YBaFe₄O₇ stabilizes the hexagonal symmetry for 0.40 ≤ x ≤ 0.70, at the expense of the cubic one. Using combined measurements of a.c. and d.c. magnetization, we establish that Ga substitution for Fe in YBaFe₄O₇ leads to an evolution from a geometrically frustrated spin glass (for x = 0) to a cationic disorder induced spin glass (x = 0.70). We also find an intermediate narrow range of doping where the samples are clearly phase separated having small ferrimagnetic clusters embedded in a spin glass matrix. The origin of the ferrimagnetic clusters lies in the change in symmetry of the samples from cubic to hexagonal (and a consequent lifting of the geometrical frustration) as a result of Ga doping. We also show the presence of exchange bias and domain wall pinning in these samples. The cause of both these effects can be traced back to the inherent phase separation present in the samples.