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Title: Magnetism and the spin state in cubic perovskite CaCo O 3 synthesized under high pressure

Cubic SrCo O 3 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 M O 3 ( M = M 4 + of transition metals, G e 4 + , S n 4 + , and Z r 4 +) 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. Here, we report a successful synthesis of the perovskite CaCo O 3 with a HPHT treatment. Surprisingly, CaCo O 3 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. Furthermore, metallic CaCo O 3 undergoes two successive magnetic transitions at 86 K and 54 K as temperature decreases. The magnetization at 5 Kmore » is compatible with the intermediate spin state t 4 e 1 of C o 4 + at the octahedral site. The thermal expansion of the Co-O bond length indicates that the population of high spin state t 3 e 2 increases for T > 100 K . The shortest Co-O bond length in cubic CaCo O 3 is responsible for delocalizing electrons in the π * -band and itinerant-electron ferromagnetism at T < 54 K . In our comprehensive comparison between SrCo O 3 and CaCo O 3 and the justification of their physical properties by first-principles calculation were made in this report. Partially filled π * and σ * bands would make CaCo O 3 suitable to study the Hund's coupling effect in a metal.« less
Authors:
 [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [1] ;  [2] ; ORCiD logo [3] ;  [4] ;  [4] ;  [5] ;  [5] ;  [4] ;  [5]
  1. Chinese Academy of Sciences (CAS) and Univ. of Chinese Academy of Sciences, Beijing (China)
  2. Chinese Academy of Sciences (CAS) , Beijing (China)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  4. Univ. of Texas, Austin, TX (United States)
  5. Chinese Academy of Sciences (CAS) and Univ. of Chinese Academy of Sciences, Beijing (China); Collaborative Innovation Center of Quantum Matter, Beijing (China)
Publication Date:
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Physical Review Materials
Additional Journal Information:
Journal Volume: 1; Journal Issue: 2; Journal ID: ISSN 2475-9953
Publisher:
American Physical Society (APS)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE
OSTI Identifier:
1376644
Alternate Identifier(s):
OSTI ID: 1371612