Pressure effect on the magnetic properties of electron-doped Sm _0.1Ca_0.9-ySr_yMnO₃ (y ≤ 0-0.3) manganites

Magnetic properties of polycrystalline Sm_0.1Ca _0.9-ySr_yMnO₃ (y ≤ 0-0.3) samples have been investigated in the temperature range 5-250K, magnetic fields up to 16kOe and under hydrostatic pressures up to 11 kbar. The studies involved sequential measurements of zero field cooled (ZFC) magnetization and measurements of magnetization upon cooling in the same magnetic field (FCC). The low-doped group (y ≤ 0-0.1) exhibits magnetic phase separation below T_N≈T _C≈100-110K, consisting of ferromagnetic (FM) clusters embedded in an antiferromagnetic (AFM) G-type matrix. Magnetization and ac-susceptibility measurements of this group of materials indicate features reminiscent of a cluster glass-like state, below T_C. It was found that the volume fraction of the FM phase at 10 K decreases with increasing y from 28% for Sm_0.1Ca_0.9MnO₃ to 18% for Sm _0.1Ca_0.8Sr_0.1MnO₃. It was found that an applied pressure enhances T_C with a pressure coefficient of dT_C/dP≈0.4-0.5Kkbar^-1. The low-temperature magnetization at this doping range (y ≤ 0-0.1) depends on pressure only slightly, except for the case of Sm_0.1Ca_0.8Sr _0.1MnO₃, where an applied pressure enhances the FM phase volume considerably. Samples with y ≤ 0.2 and 0.3 exhibit a heterogeneous spin configuration in their ground state, consisting of a C-AFM phase and a G-AFM phase with a very weak FM moment. The temperature of transition from the paramagnetic to the C-AFM state is almost insensitive to applied pressure, whereas the lower transition temperature to the G-AFM state increases slightly under pressure. It was found also that an applied pressure considerably reduces the FM correlations in the paramagnetic phase as well as the FM component of the G-AFM state.