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2009 MAGNETIC SYSTEMSField-induced transitions in RECo 0.50 Mn 0.50 O 3 (RE = Dy, Eu)One interesting family of perovskites is RE(TM,Mn)O 3 inwhich the Mn atom has been partially substituted by atransition-metal element TM like Co giving rise to Mn 4+ -Co 2+ ferromagnetic interactions. In addition, if the RE elementbears a large magnetic moment, then the RE sublatticemay interact with the ordered TM-Mn sublattice [Peñaet al., J. Magn. Magn. Mater. 312, 78 (2007); Antuneset al., J. Europ. Ceram. Soc. 27, 3927 (2007)]. Inthis work we present the magnetic properties of bulk ceramicsamples EuCo 0.50 Mn 0.50 O 3 and DyCo 0.50 Mn 0.50 O 3 .Nickel-containing samples of similar composition (Ni/Mn= 0.50/0.50) are measured for comparison. Samples wereprepared by solid state synthesis from the correspondingsubmicronic powder oxides. They were characterized byX-ray diffraction showing pure perovskite orthorhombicstructure (Pbnm). Magnetic measurements were performedon specimens cut from ceramic bulks.ZFC curve follows a similar behaviour as the Eu case, thatis canted antiferromagnetism since the magnetic propertiesof the Co-Mn sublattice predominate. When the sampleis field cooled the Co-Mn sublattice orders at T C = 85 K,a lower temperature as the Eu-case because of the smallerionic radius of the Dy ion compared to Eu.The magnetization loop is shown in figure 130(a) forEuCo 0.50 Mn 0.50 O 3 sample. We notice five steep transitionson the hysteresis curves. The magnetization valuemeasured at 20 T is lower than the theoretical value(M S = 3.87 µ B ) if we consider all the spins of Mn 4+and Co 2+ aligned and no contribution from Eu 3+ . ForEuNi 0.50 Mn 0.50 O 3 there are no step-like transitions. Themeasured value of the magnetization at 20 T is also lowerthan the calculated value of 3.35 µ B if all spins of transitionmetals are aligned on the field direction. This suggeststhat Eu 3+ in these systems is a classical case of VanVleck magnetism. For DyCo 0.50 Mn 0.50 O 3 (figure 130(b))we can see two field transitions (near 2 T and 5 T) andthe magnetization measured at 20 T reaches the theoreticalvalue (M S = 6.76 µ B ) if we consider a ferrimagneticmodel of two sublattices (rare earth and transition metalones) fully aligned, one in opposition to the other. For theDyNi 0.50 Mn 0.50 O 3 sample we do not see any field-inducedanomaly on the hysteresis curves up to 20 T.Figure 129: Thermal dependence of the ZFC-FC magnetizationfor EuCo 0.50 Mn 0.50 O 3 and DyCo 0.50 Mn 0.50 O 3 measured at0.025 T.Temperature dependence of the magnetization is shown infigure 129 for EuCo 0.50 Mn 0.50 O 3 and DyCo 0.50 Mn 0.50 O 3 .Samples were first cooled under no magnetic field, thenthe static field of 0.025 T was applied and samples allowedwarming until 300 K (ZFC). Then, they were subsequentlycooled under the same static field (FC). ZFC branch forEu sample shows that, upon warming, the Co-Mn sublatticeorders in an antiferromagnetic state with a small ferromagneticcomponent due to non-linearity of the spins. Thelow magnetic moment of Eu and the low external field appliedto the sample, result in almost no contribution fromEu. During the FC procedure, the transition metal sublatticeorders ferromagnetically at T C = 130 K. For the Dysample we can notice that the ZFC curve starts from a finitevalue at 2 K and decreases to almost zero when thetemperature increases. This is just due to the Curie-Weissbehaviour of Dy 3+ that follows 1/T law, typical of freespinnon-correlated moments. For higher temperatures, theFigure 130: Magnetization loop at2.5K for (a) EuCo 0.50 Mn 0.50 O 3 (insert: EuNi 0.50 Mn 0.50 O 3 ) and(b) DyCo 0.50 Mn 0.50 O 3 (insert: DyNi 0.50 Mn 0.50 O 3 ).A. B. AntunesO. Peña (Sciences Chimiques de Rennes, Université de Rennes 1, Rennes, France), C. Moure, A. Moure (Electrocerámicas,Instituto de Cerámica y Vidrio, CSIC, Madrid, Spain)91