The $\mathrm{A}\mathrm{B}{\mathrm{O}}_3$ type manganites ${\left(\mathrm{La}\mathrm{R}\right)}_{0.45}{\left(\mathrm{Ca}\mathrm{Sr}\right)}_{0.55}\mathrm{Mn}{\mathrm{O}}_3$ ($\mathrm{R}={\mathrm{Eu}}^{3+}$—a nonmagnetic ion and ${\mathrm{Tb}}^{3+}$—a magnetic ion) which possess large A-site size-disorder, exhibit metamagnetic transitions as a function of magnetic field. Below a certain crossover temperature and depending on the magnetic field sweep rate, the metamagnetic transition transforms from a broad to sharp step-like transitions. This crossover temperature increases on increasing the field sweep rate. The effect of field sweep rate on the critical field of metamagnetic steps decreases with decreasing temperature. This along with the magnetic relaxation and specific heat data provide clear evidence on the contribution of spin-lattice coupling in determining the transformation from smooth to sharp magnetic transitions. These studies also suggest that the A-site magnetism has no important role in transformation from reversible to irreversible magnetization.

• Received 26 September 2005

DOI:https://doi.org/10.1103/PhysRevB.73.064407