The effect of high pressure (0–8 GPa) on the magnetic structure of polycrystalline samples of ${\text{La}}_{0.5}{\text{Ca}}_{0.5-x}{\text{Sr}}_x{\text{MnO}}_3$ $\left(0.1\le x\le 0.4\right)$ 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 $T_{\text{N}}\sim 150\text{K}$. 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 $T<T_{\text{N}}$ $\left(\sim 250\text{K}\right)$. 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 ${\sigma }^2$. We observe that pressure required for destabilizing the CE-type antiferromagnetic state is reduced with increasing disorder ${\sigma }^2$. External pressure and changing $A$-site ionic radii have analogous effect on the magnetic structure.

• Received 26 November 2009

DOI:https://doi.org/10.1103/PhysRevB.81.104424