Eur. Phys. J. B (2013) 86: 435
https://doi.org/10.1140/epjb/e2013-40617-x

Regular Article

Pressure induced antiferromagnet-ferromagnet transition in La_0.5Ba_0.5CoO_2.8 cobaltite

¹ Scientific-Practical Materials Research Centre NAS of Belarus, 220072 Minsk, Belarus
² Karlsruhe Institute of Technology, 76131 Karlsruhe, Germany
³ Joint Institute for Nuclear Research, 141980 Dubna, Russia
⁴ Institut Laue-Langevin, 38042 Grenoble Cedex 9, France
⁵ Helmholtz-Zentrum Berlin, 14109 Berlin, Germany

^a e-mail: troyan@physics.by

Received: 25 June 2013
Received in final form: 21 August 2013
Published online: 16 October 2013

Abstract

The anion deficient cobaltite La_0.5Ba_0.5CoO_2.8 with the formal cobalt valence state close to 3+ has been studied as function of pressure up to 6.5 GPa at different temperatures by neutron powder diffraction. At ambient pressure the crystal structure of this compound has cubic symmetry (space group Pm3̅m) and is found to become antiferromagnetic with T_N close to 250 K. Applied pressure induces a gradual transition from the antiferromagnetic into a ferromagnetic state through a mixed magnetic state. The transition is not accompanied by obvious changes in the macroscopic crystal symmetry. It is suggested that the magnetic ground state strongly depends on the unit cell volume and that the transition is associated with a spin state crossover of the cobalt ions whereas the formal Co³⁺/Co⁴⁺ ratio is less important than expected following the double exchange scenario for the appearance of ferromagnetism.