Unusual Zero field cooled Exchange bias and related mechanism in YBaCuFeO5-Ni0.3Zn0.7Fe2O4 Composites

Abstract

We report an unusual room temperature giant zero field cooled exchange bias (~1kOe) in an antiferromagnetic (100-x)YBaCuFeO5–ferrimagnetic (x) Ni0.3Zn0.7Fe2O4 composite. Solid state route is adopted to prepare these dilute weight% (x = 1, 3 and 5) ferrite based composites. Incommensurate to commensurate magnetic transition (TN2) of YBaCuFeO5 [1] is shifted to high temperature by 10 K with lowest concentration and indistinguishable in higher concentrations due to magnetic dominance of ferrites. The irreversibility of magnetization due to the field history mostly stems from the uncompensated spins and a competitive interaction among the magnetic phases at the interface. The magnetic isotherms show unusual negative exchange bias phenomena in the said system and a large room temperature spontaneous exchange bias (~1 kOe) is achieved with a dilute incorporation x = 5. The exchange bias field and coercive fields (HC) are however contrary to each other with temperature (and concentration) explained with a schematic model on the basis of dominating irreversible spins at high temperature. In a field of ±50 kOe, the exchange bias field is dropped while HC is increased, which might be due to the dominance of Zeeman energy over the uniaxial anisotropy [2]. Non-collinear magnetic phase transition of YBaCuFeO5 at T ≤ 175 K plays a pivotal role in reducing the exchange bias as compare to its collinear phase (300 K). Moreover, the extent of this bias field (~1 kOe) can be considered a useful component in efficient device fabrication.