Pressure effects on the magnetic structure in La 0.5 Ca 0.5 − x Sr x MnO 3 ( 0.1 ≤ x ≤ 0.4 ) manganites

The effect of high pressure (0\char21{}8 GPa) on the magnetic structure of polycrystalline samples of ${\text{La}}_{0.5}{\text{Ca}}_{0.5\ensuremath{-}x}{\text{Sr}}_{x}{\text{MnO}}_{3}$ $(0.1\ensuremath{\le}x\ensuremath{\le}0.4)$ manganites at 5 K is investigated using neutron-diffraction technique. Application of pressure is found to modify the previously reported magnetic structure, observed under ambient conditions, in these compounds [I. Dhiman et al., Phys. Rev. B 77, 094440 (2008)]. In $x=0.1$ composition, at 4.6(2) GPa and beyond, $A$-type antiferromagnetic structure is found to coexist with charge-exchange (CE)-type antiferromagnetic phase, observed at ambient pressure, with ${T}_{\text{N}}\ensuremath{\sim}150\text{ }\text{K}$. For $x=0.3$ sample, as a function of pressure the CE-type phase is fully suppressed at 2.3(1) GPa and $A$-type antiferromagnetic phase is favored. Further Sr doping at $x=0.4$, the $A$-type antiferromagnetic phase is observed at ambient pressure and for $Tl{T}_{\text{N}}$ $(\ensuremath{\sim}250\text{ }\text{K})$. This phase is retained in the studied pressure range. However, the magnetic moment progressively reduces with increasing pressure, indicating the suppression of $A$-type antiferromagnetic phase. The present study brings out the fragile nature of the CE-type antiferromagnetic state in half-doped manganites as a function of pressure and disorder ${\ensuremath{\sigma}}^{2}$. We observe that pressure required for destabilizing the CE-type antiferromagnetic state is reduced with increasing disorder ${\ensuremath{\sigma}}^{2}$. External pressure and changing $A$-site ionic radii have analogous effect on the magnetic structure.