Giant exchange bias effect in Ruddlesden-Popper oxides SrLaFe0.25+xMn0.25Co0.5−xO4 (x=0,0.25): Role of the cluster glass magnetic phase in a quasi-two-dimensional perovskite
Résumé
Structural and magnetic studies on SrLa(Fe 0.25 Mn 0.25)Co 0.5 O 4 (FMC1) and SrLaFe 0.5 (Mn 0.25 Co 0.25)O 4 (FMC2) reveal unusually large exchange bias behavior in these atomically disordered quasi-two-dimensional layered perovskites. Powder x-ray as well as neutron diffraction confirm tetragonal crystal structure with I4/mmm space group for both the compounds. Magnetization measurements on FMC1 as well as FMC2 reveal short-range antiferromagnetic ordering around room temperature and frozen magnetic clusters at lower temperatures (T < 23 K for FMC1 and T < 43 K for FMC2). The random occupancy of mixed-valent magnetic ions (Fe 3+ /Fe 4+ , Mn 3+ /Mn 4+ , Co 2+ /Co 3+) at the perovskite octahedral sites give rise to locally varying competing antiferromagnetic and ferromagnetic exchange interactions, resulting in low temperature frozen spin states. Giant exchange bias values of ∼6 and ∼9.5 kOe were observed for FMC1 and FMC2, respectively, at 2 K under an applied field of 50 kOe. In comparison, the Co-rich FMC1 exhibits higher magnetization and coercivity, whereas Fe-rich FMC2 possesses a higher exchange bias effect. Our experimental results reveal compositional tuning induced exotic magnetic behavior in quasi-two-dimensional layered oxides.
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