Effect of A-site ionic radius on metamagnetic transition in charge ordered Sm_(0.5)(Ca_(0.5-y)Sr_(y))MnO₃ compounds

We investigate the ultra-sharp jump in the isothermal magnetization and the resistivity in the polycrystalline $Sm_{0.5}(Ca_{0.5-y}Sr_{y})MnO_3$ $(y = 0, 0.1, 0.2, 0.25, 0.3, 0.5)$ compounds. The critical field $(H_{cr})$, required for the ultra-sharp jump, decreases with increase of `Sr' concentration, i.e. with increase of average A-site ionic radius $\langle r_A\rangle$. The magnetotransport data indicate that the phase separation increases with the increase of $\langle r_A\rangle$, i.e. with $y$. The dependency of $H_{cr}$ with magnetic field sweep rate reveals that the ultra-sharp jump from antiferromagnetic (AFM) state to the ferromagnetic (FM) state is of martensitic in nature. Our two-band double exchange model Hamiltonian calculations show that the `Sr' doping induces the ferromagnetic clusters in the antiferromagnetic insulating phase and in turn reduces the critical field. In the end we present a phenomenological picture obtained from our combined experimental and theoretical study.