Magnetic and structural phase transitions in La_0.5Sr_0.5CoO_3−δ(0 ≤ δ < 0.3) cobaltites

Abstract

The evolution of the crystal structure and the magnetic properties was investigated in the La0.5Sr0.5CoO(3-δ) (0 < δ < 0.3) system as a function of the oxygen deficit δ. Compounds with a low oxygen deficit (δ < 0.1) are shown to be predominantly ferromagnetic, while further increase (δ > 0.1) gradually changes the magnetic structure from ferromagnetic to G-type antiferromagnetic and causes a structural transition from rhombohedral to cubic symmetry. Resistivity and magnetoresistance at low temperature increase with increasing of oxygen vacancies. It is argued that oxygen reduction facilitates stabilization of the high spin state of Co(3+) ions. Antiferromagnetic interactions between cobalt ions in the high spin state are found to dominate in compounds with the oxygen deficit δ > 0.18.

Possible surface antiferromagnetism and no evidence for intergranular tunneling magnetoresistance in La0.5Sr0.5CoO3–δ cobaltites

“…One can suggest that the gradual magnetic transition is accompanied by a growth of the antiferromagnetic phase as it was observed by neutron powder diffraction of La 0.5 Sr 0.5 CoO 2.83 compound. 8 The isothermal magnetization measured at 5 K is lower than that at 40 K and there is a very weak tendency to saturation in a magnetic field up to 14 T ( Fig. 2(b)).…”

“…The oxygen deficit gradually stabilizes the antiferromagnetic phase and antiferromagnetic ordering in La 0.5 Sr 0.5 CoO 2.83 occurs around 170 K as it was evidenced by neutron powder diffraction. 8 According to Goodenough-Kanamori rules (Ref. 1), the superexchange magnetic interactions between cobalt ions in HS state should be strong and negative.…”

“…6) can be ascribed to field induced spin state transition from antiferromagnetic into ferromagnetic phase. 7,8 This transition was suggested to occur via structural distortion induced by magnetic field. 7,8 The structural distortion stabilizes the IS state and destabilizes both HS and LS states.…”

“…The oxygen deficit stabilizes an antiferromagnetic phase in both La 0.5 Ba 0.5 CoO 3-d and La 0.5 Sr 0.5 CoO 3-d series. [6][7][8] It was suggested that the magnetic moment of 1.5 l B in metallic La 0.5 Sr 0.5 CoO 3 can be rationalized with an intermediate-spin model having localized t 5 2g configurations on each cobalt ion and an narrow itinerant r* band containing 0.5 electrons per Co atom magnetized ferromagnetically. 9 However, according to Refs.…”

Giant positive magnetoresistance in half-metallic double-perovskite Sr 2 CrWO 6 thin films

“…The oxygen vacancies have different effects on the SCWO films and the STO substrate. For the metallic SCWO films, they can increase the scattering of the electrons and the resistivity of the materials, which can even possibly lead to the semiconductor behavior due to the defective band that crosses the Fermi level ( 36 – 42 ). However, as shown above, the resistivity of the three films is very small, which is comparable to that of the best metals.…”