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

Abstract

Structural and magnetic studies on $\mathrm{SrLa}({\mathrm{Fe}}_{0.25}{\mathrm{Mn}}_{0.25}){\mathrm{Co}}_{0.5}{\mathrm{O}}_{4}$ (FMC1) and ${\mathrm{SrLaFe}}_{0.5}({\mathrm{Mn}}_{0.25}{\mathrm{Co}}_{0.25}){\mathrm{O}}_{4}$ (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 ($Tl23\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for FMC1 and $Tl43\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ for FMC2). The random occupancy of mixed-valent magnetic ions ($\mathrm{F}{\mathrm{e}}^{3+}/\mathrm{F}{\mathrm{e}}^{4+}, \mathrm{M}{\mathrm{n}}^{3+}/\mathrm{M}{\mathrm{n}}^{4+}, \mathrm{C}{\mathrm{o}}^{2+}/\mathrm{C}{\mathrm{o}}^{3+}$) 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 \ensuremath{\sim}6 and \ensuremath{\sim}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.