Exchange-bias (EB) phenomena have been observed in the $L_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Mn}{\mathrm{O}}_3$ ($L=\mathrm{Y}$, ${\mathrm{Y}}_{0.5}{\mathrm{Sm}}_{0.5}$, and ${\mathrm{Y}}_{0.5}{\mathrm{La}}_{0.5}$)-type manganites showing cluster-glass-like and spin-glass-like behavior. The field cooled magnetic hysteresis loops exhibit shifts both in the field and magnetization axes. The values of exchange field $\left(H_E\right)$, coercivity $\left(H_C\right)$, remanence asymmetry $\left(M_E\right)$, and magnetic coercivity $\left(M_C\right)$ of $L_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Mn}{\mathrm{O}}_3$ are found to depend strongly on temperature, measuring field, as well as strength of cooling field $H_{\mathrm{cool}}$. $H_E$ increases sharply with the magnitude of $H_{\mathrm{cool}}$ $(⩽3\mathrm{T})$, but for larger $H_{\mathrm{cool}}$ $(>3\mathrm{T})$, it decreases due to the growth of the ferromagnetic cluster size. This observed behavior has been explained in terms of interfacial exchange coupling between coexisting ferromagnetic cluster glass and the disordered spin-glass-like phases, where the spin configurations are strongly affected by the cooling field strength. Below the spin and/or cluster glass freezing temperature $\left(T_f\right)$, both $H_E$ and $M_E$ decrease exponentially with temperature. The value of $H_C$ increases almost exponentially with increasing magnetic-field step size $\left(\Delta H\right)$. In addition, the observed training effect of the EB behavior has been explained well in terms of the existing relaxation model developed for other classical EB systems. In view of the use of manganites in spintronics, the present observation of EB-like shift even in the mixed valent polycrystalline manganites such as $L_{0.5}{\mathrm{Sr}}_{0.5}\mathrm{Mn}{\mathrm{O}}_3$ is of paramount importance.

• Received 16 July 2007

DOI:https://doi.org/10.1103/PhysRevB.77.144409