Spin dynamics and spin-glass state in Fe-doped cobaltites

Abstract

A thorough study of the magnetic and transport properties of La0.5Sr0.5Co1−xFexO3 (0⩽x⩽0.6) compounds has been made. The Fe substitution destroys the metallic state and the resistivity increases by orders of magnitude even with a very small extent of Fe substitution. The charge localization due to Fe substitution is likely to have its origin in the electronic configuration rather than in its ionic size. The hole-poor regions, corresponding to the Fe-rich regions, would also dilute the magnetic lattice and thereby prevent the occurrence of long-range order. Spin-glass behavior was observed for x⩾0.5 compositions and is ascribed to the frustration of random competing exchange interactions, namely the ferromagnetic double-exchange interaction between Co3+ and Co4+, and the antiferromagnetic interactions like Co-O-Fe and Fe-O-Fe. A dynamic scaling analysis of ac susceptibility data using conventional critical slowing down indicates a finite spin-glass phase-transition temperature Tg≈85 K and a dynamic exponent zv≈12.4, for x=0.5 composition.

Magnetic frustration effects in Fe-doped cobalt oxides

“…With increasing Fe-doped content, E a increases and T min decreases, indicating the lowering of ferromagnetic interactions for which the Curie temperature decreases. These results are consistent with the magnetization and resistivity data [5]; the Fe substitution destroyed the metallic state and the resistivity increases by orders of magnitude even with a very small extent.…”

“…2, for example, the x ¼ 0:4 sample]. This is probably due to an additional appearance of AFM Fe-O-Fe superexchange interactions that, together with the existing AFM Co-O-Fe interaction, suppress strongly the ferromagnetism and conductivity [5]. The strong development of the AFM phase also destroyed the ferromagnetic order and thereby results in the observed magnetic glassy behavior in the sample with x40:4 compositions (see Fig.…”

“…[5] that the Fe substitution in La 0.5 Sr 0.5 Co 1Àx Fe x O 3 led to a considerable decrease in the Curie temperature, Table 1 To further elucidate the internal dynamics of La 0.5 Sr 0.5 Co 1Àx Fe x O 3 compounds, in the present work, we measured EPR spectra of the samples (see Fig. 2).…”

“…Coming up to what we assumed, a detailed study of spin dynamics, spinglass and cluster-glass properties of La 0.5 Sr 0.5 CoO 3 by substituting Fe for Co has been made by means of resistivity, DC magnetization, and AC susceptibility measurements [5]. In this work, we focus mainly on discussing magnetic frustration effects in these Fe-doped cobalt oxides by analyzing electron paramagnetic resonance (EPR) spectra in connection with the other experimental data [5]. La 0.5 Sr 0.5 Co 1Àx Fe x O 3 (0pxp0:6) polycrystalline samples were prepared by the conventional solid-state reaction method.…”

Impact of the Fe doping on magnetism in perovskite cobaltites

“…In the present paper, we choose Fe element as the substitution ion. The effect of Fe doping in La 1−x Sr x CoO 3 has been studied by several groups, [34,35,36,37,38] and the common conclusion is the suppression of ferromagnetism and metallicity with Fe [17,39] it is not suitable to be used for investigating the magnetic interactions between Co and Fe ions. Therefore, we choose two systems with less Ca content, which do not exhibit spin-state transition at low temperature.…”