Effects of substitution at the manganese site in RE(Ni,Mn)O3 perovskites (RE=Y, Eu)

The magnetically ordered states of the YNixMn1−xO3 and EuNixMn1−xO3 solid solutions (0.0≤x≤0.50) have been studied at different temperatures and magnetic fields. The magnetization as a function of temperature M(T) shows features due to canted-antiferromagnetism (x=0.25 and 0.33) and ferromagnetism (x=0.50), while YNi0.20Mn0.80O3 presents a spin-glass behavior. A large field-dependence of the susceptibility maximum at Tmax is found in the nickel-poor region, except for the spin-glass compound, for which Tmax stays constant at TSG∼20 K. For the nickel-rich samples the paramagnetic-to-ferromagnetic transition at Tc is field-independent, with Tc∼80 and 150 K, for YNi0.50Mn0.50O3 and EuNi0.50Mn0.50O3, respectively. The coercive field Hcoerc and the high-field data obtained from magnetization loops M(H) show a well-defined frontier at x=xcrit=1/3, between canted-antiferromagnetism (x≤xcrit) and full ferromagnetism (x>xcrit). This critical value corresponds to equal amounts of Mn3+ and Mn4+, leading to a maximum number of pairs Mn3+/Mn4+ and an optimum in the double-exchange interactions.