Isomorphism in the Bi1.8Fe1.2(1−x)Ga1.2xSbO7 pyrochlores with spin glass transition

Abstract

A series of Bi1.8Fe1.2(1−x)M1.2xSbO7 (M = Ga, Al) compositions with substitution of Fe3+ for diamagnetic Ga3+ and Al3+ has been synthesized and characterized by XRD, Mössbauer spectroscopy and magnetic measurements. X-ray diffraction analysis indicate that the Bi1.8Fe1.2(1−x)Ga1.2xSbO7 (x = 0–1) at the whole x range and Bi1.8Fe0.84Al0.36SbO7 (x = 0.3) are solid solutions of pyrochlore structure. With an increase of Ga3+ content the substitution of Fe3+ for Ga3+ occurs disproportionally over A- and B-sites while Al3+ ion incorporates entirely on B-site. Magnetic measurements showed that all studied compositions fall into the category of disordered, magnetically frustrated materials and at T ≤ 13 K undergo spin-glass transition. The spin-glass phases have a striking sensitivity to substitution of Fe3+ for Ga3+ or Al3+. The comparison of the magnetic behavior of Ga- and Al-containing pyrochlores revealed that, most likely, freezing temperature is governed by Fe3+ ions residing especially on octahedral B-sites.