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Inter-network magnetic interactions in GdMexMn1 xO3 perovskites (Me ¼ transition metal)

AutorPeña, Octavio; Antunes, A. B.; Martínez, G.; Gil, Vanesa; Moure Jiménez, Carlos
Fecha de publicación2007
CitaciónJournal of Magnetism and Magnetic Materials 310 (2007) 159–168
ResumenThe gadolinium-based manganite GdMnO3 of perovskite structure has been partially substituted at the manganese site by transition metal elements Me like Cu, Ni and Co, leading to a general formula GdMexMn1 xO3, in which different magnetic entities (e.g., Gd3+, Cu2+, Ni2+, Co2+, Co3+, Mn3+, Mn4+) can coexist, depending on charge equilibrium conditions. For divalent cations such as Cu2+ and Ni2+, the solid solution extends from x(Me) ¼ 0–0.5, with O-type orthorhombic symmetry aoc= p 2ob . When the substituting element is cobalt, the solid solution extends over the whole range [0pxp1], changing from O0-type symmetry c= p 2oaob to O-type for x40.5. In this latter case, the synthesis is performed under oxygen flow, which allows the cobalt ion to take a 3+ oxidation state. Magnetic properties were studied through susceptibility and magnetization measurements. A paramagnetic–ferromagnetic transition occurs at Tc, due to double-exchange interactions between transition metal ions (Mn3+–Mn4+, Ni2+–Mn4+, Co2+–Mn4+), leading to an optimum value at x(Me) ¼ 0.50 (Tc ¼ 145 and 120 K, for GdNi0.5Mn0.5O3 and GdCo0.5Mn0.5O3, respectively). Different situations were identified, among them, a spin reversal in GdNi0.3Mn0.7O3, strong ferromagnetic interactions in GdNi0.5Mn0.5O3, large coercive fields in GdCo0.5Mn0.5O3 or Co3+–Mn4+ antiferromagnetic interactions in GdCo0.9Mn0.1O3. Most of these situations are explained by a phenomenological model of two magnetic sublattices: a transition-metal |Me+Mn| network which orders ferromagnetically at Tc and a gadolinium sublattice, composed of independent Gd3+ ions. These networks are antiferromagnetically coupled through a negative exchange interaction. The local field created by the ferromagnetic |Me+Mn| lattice at the gadolinium site polarizes the Gd moment in a direction opposite to the applied field. When the magnetization of paramagnetic gadolinium, which varies as T 1, gets larger than the ferromagnetic magnetization of the transition metal, which is ‘‘frozen’’ at ToTc, then the total magnetic moment changes its sign, leading to an overall ferrimagnetic state.
Versión del editorhttp://dx.doi.org/doi:10.1016/j.jmmm.2006.08.004
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