Interface-sustained magnetic properties displayed by the La2 O3 -SrO- Co2 O3 nanocomposite

Abstract

The heterogeneous metal oxide composite (1-x) La2 O3 xSrO Co3 O4 (where x≥0.8), comprised primarily of the three oxide phases (La2 O3, spinel Co3 O4, and SrO), exhibits a special temperature-magnetic response profile. The coercivity of the composite decreases with increasing temperature from 70 to 200 K, but increases from 200 to 298 K. This outcome is upheld because of the occurrence of three structures, which are the perovskite La1-α Srα Co O3-Β (α≪x) phase that is formed at the interface region of the above three oxides, the presence of La3+ in the Co3 O4 phase, and the interface between SrO and Co3 O4 phases (domains). The first two structures are deemed responsible for manifestation of ferromagnetism at low temperature, while the last one for room temperature ferromagnetism. We also noted that the third structure could reveal noticeable magnetic properties only when the three major oxide phases are mixed in nanometer scale as the magnetic behavior is triggered through the deformation of octahedral Co-O cells located at the surface of the spinel domains. To realize such an ultrahigh dispersion of the three oxide phases, pyrolysis of the metal-ion-containing hydrogel made of the three metal ions (La3+, Sr2+, and Co2+) and organic moieties (e.g., citric acid and glycine) is an effective approach. In contrast to the homogeneous perovskite solid solution La1-x Srx Co O3-δ (x≤0.5), the present type of composite shows stronger coercivity but weaker remanence induction at temperatures below 200 K. Other than the temperature effect, the influence of the organic components in the metal-ion-containing hydrogel on the interface-sustained magnetism has also been studied. © 2005 American Institute of Physics.