Metal-insulator transition induced by a spin-state transition inTbBaCo2O5+δ (δ

Room-temperature ferromagnetism inSr1−xYxCoO3−δKobayashi1, Ishiwata2, Terasaki3 et al. 2005Phys. Rev. B9214780View full textAdd to dashboardCite

“…In recent years, the A-site ordered perovskite RBaCo 2 O 5.5 (R = rare earth element) has been intensively studied [8,9,10]. It shows a ferromagnetic transition around 300 K (higher than T c of La 1−x Sr x CoO 3 ) with giant magnetoresistance [8,11].…”

“…The complicated magnetism has been explained as follows: The Co 3+ ions in the intermediate spin (IS) state of S = 1 exhibit an orbital ordering at 350 K along the a axis [9], which induces ferromagnetic interaction along the a axis. On the other hand, antiferromagnetic interaction is expected along the b axis because of the conventional superexchange, which causes the antiferromagnetic order below 270 K. At higher temperatures, thermally ex- * Electronic address: kobayashi-wataru@suou.waseda.jp cited carriers induce the double-exchange interaction to align the ferromagnetic chains, and stabilizes the ferromagnetic state from 270 to 300 K [8,9].…”

Effects of partial Co replacement by Fe in Sr0.775Y0.225CoO3-δ on its magnetic property, oxygen deficiency and crystal structure

“…A higher T C of around 300 K was later reported in cobalt oxide RBaCo 2 O 5.5 (R = rare earth element) [3,11], where only Co 3+ was found in the compound, implying the irrelevance of the conventional double exchange interaction for the appearance of ferromagnetic ordering. For R = Tb [5], the ferromagnetic coupling of the spins was suggested to be driven by orbital ordering along the a-axis at 340 K, with antiferromagnetic coupling appearing along the b-axis at 260 K due to superexchange interaction. The bulk ferromagnetic phase is believed to be stabilized at the higher temperature of 300 K as a result of spin state transition of Co 3+ from IS to HS [5], while LS to HS transition was found in similar range of temperature for R = Gd [3,11] due to oxygen vacancy ordering reported for this compound [3].…”

“…For R = Tb [5], the ferromagnetic coupling of the spins was suggested to be driven by orbital ordering along the a-axis at 340 K, with antiferromagnetic coupling appearing along the b-axis at 260 K due to superexchange interaction. The bulk ferromagnetic phase is believed to be stabilized at the higher temperature of 300 K as a result of spin state transition of Co 3+ from IS to HS [5], while LS to HS transition was found in similar range of temperature for R = Gd [3,11] due to oxygen vacancy ordering reported for this compound [3]. These developments were recently followed by the discovery of new A-site ordered perovskite Co-oxides of Sr 1−x R x CoO 3 (R = Y and lanthanide) as independently reported by Withers et al [12,13] and Istomin et al [14,15].…”

“…Among many well-known transition metal oxides, perovskite cobalt oxides have emerged as a new distinct class of materials offering a variety of fascinating physical phenomena and potentially useful physical properties, such as ferromagnetism [1], thermoelectricity [2], giant magnetoresistance [3][4][5] and multiferroism [6]. The rich physical and complex properties of the materials are largely due to the possible presence of multi-valence states of cobalt ions in the compounds, namely Co 2+ , Co 3+ , Co 4+ or the intermediate mixed valence states, which are associated with structural and compositional variations of the system, giving rise to various charge and orbital ordering phases.…”