From A-type antiferromagnetism to ferromagnetism in half-doped perovskite manganites

We have studied by neutron diffraction, resistivity and magnetization measurements the variation of the structural, magnetic and electric properties as a function of the cation size mismatch at the perovskite A-site. The four selected compounds RE _0.5AE _0.5MnO ₃, with extremely large A-site cation size < r_A>=1.25-1.28 Å, correspond to two < r_A> values and for each < r_A>, two mismatch values have been retained. This study shows that the decrease of σ² is an essential factor in stabilization of the ferromagnetism. As a result, the Curie temperature is markedly increased for the samples with smaller σ², even if they exhibit a complex ferromagnetic/antiferromagnetic phase-separated state at low temperature.