Magnetism and the spin state in cubic perovskite CaCo⁢O3 synthesized under high pressure

Release time:2017-07-17  Hits:

• DOI number:10.1103/PhysRevMaterials.1.024406
• Journal:Physical Review Materials
• Abstract:Cubic SrCo⁢O3 with an intermediate spin state can only be stabilized by high pressure and high temperature (HPHT) treatment. It is metallic and ferromagnetic with the highest Curie temperature of the transition-metal perovskites. The chemical substitution by Ca on Sr sites would normally lower crystal symmetry from cubic to orthorhombic as seen in the perovskite family of Ca⁢��⁢O3 (��=��4+ of transition metals, G⁢e4+, S⁢n4+, and Z⁢r4+) at room temperature. This structural change narrows the bandwidth, so as to further enhance the Curie temperature as the crossover to the localized electronic state is approached. We report a successful synthesis of the perovskite CaCo⁢O3 with a HPHT treatment. Surprisingly, CaCo⁢O3 crystallizes in a simple cubic structure that remains stable down to 20 K, the lowest temperature in the structural study. The new perovskite has been thoroughly characterized by a suite of measurements including transport, magnetization, specific heat, thermal conductivity, and thermoelectric power. Metallic CaCo⁢O3 undergoes two successive magnetic transitions at 86 K and 54 K as temperature decreases. The magnetization at 5 K is compatible with the intermediate spin state ��4⁢��1 of C⁢o4+ at the octahedral site. The thermal expansion of the Co-O bond length indicates that the population of high spin state ��3⁢��2 increases for ��>100K. The shortest Co-O bond length in cubic CaCo⁢O3 is responsible for delocalizing electrons in the ��*-band and itinerant-electron ferromagnetism at ��<54K. A comprehensive comparison between SrCo⁢O3 and CaCo⁢O3 and the justification of their physical properties by first-principles calculation have also been made in this report. Partially filled ��* and ��* bands would make CaCo⁢O3 suitable to study the Hund's coupling effect in a metal.
• Translation or Not:no
• Date of Publication:2017-01-01
• Links to published journals:https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.1.024406