Control of the magnetic ground state by A-site substitution in Pr_0.6Ca_0.4MnO₃: Impact upon the multistep-like behavior of magnetization

The substitution of barium and strontium for calcium in the pseudo-charge exchange (CE)-type charge ordered manganite Pr_0.6Ca_0.4MnO₃ has been reinvestigated for low substitution levels (≪10%). It is shown that Ba or Sr substitution exhibits a greater ability to induce ferromagnetism, metallicity and sharp magnetization, and resistivity multisteps at low temperature (2.5 K) in this phase, than in the CE-type manganite Pr_0.5Ca_0.5MnO₃. The crucial role of the size of the A-site impurity is emphasized, the larger Ba²⁺ cation being much more efficient than Sr²⁺ to induce such effects. This study demonstrates that the multistep-like behavior, previously observed for Mn-site substitution in Pr_0.6Ca_0.4MnO₃, can be obtained by A-site substitution, Ba substitution being as efficient as Cr substitution, and Sr substitution having a similar effect to Ga substitution. In the framework of the martensitic mechanism, it is suggested that the introduction of larger cations on the Ca sites, or of non-Jahn–Teller cations on the Mn³⁺ sites, induces “locally” around them the formation of more symmetric domains within the distorted antiferromagnetic matrix. This structural phase separation would induce the electronic phase separation, favoring the formation of ferromagnetic metallic regions in the antiferromagnetic insulating matrix. © 2004 American Institute of Physics.