Ferromagnetic state of La 1-xBa xCoO 3 under applied pressure: Factors controlling the sign reversal of pressure effect in cobaltites

I. Fita, R. Szymczak, R. Puzniak, A. Wisniewski, I. O. Troyanchuk, D. V. Karpinsky, V. Markovich, H. Szymczak

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Abstract

Pressure effect on magnetic properties of polycrystalline La 1-xBa xCoO 3 (0.1 ≤ x ≤ 0.5) was studied by magnetization measurements in the temperature range 5-240 K, magnetic field up to 16 kOe, and under hydrostatic pressure up to 10.5 kbar. For low-doped cobaltites (x=0.1,0.15), it was found that applied pressure enhances the ferromagnetic (FM) cluster phase, resulting in an increase of both spontaneous FM moment and transition temperature of clusters TCcl, while the freezing temperature T f lowers under pressure appreciably (dT f/dP ≈ -1.4 K/kbar), suggesting the weakening of interaction between clusters. For higher-doped La 1-xBa xCoO 3 (0.2 ≤ x ≤ 0.5), having developed long-range FM order, the systematic increase of T C under pressure was observed with coefficient dT C/dP linearly increasing with doping up to 1.8 K/kbar at x=0.5, the highest value reported for cobaltites. The positive value of the dT C/dP coefficient found for the Ba compound in a whole range of studied doping is in strong contrast to that found in Ca and Sr cobaltites, where the dT C/dP was found to change a sign from a negative to a positive one with increasing doping. It is shown that the sign reversal of the dT C/dP coefficient for La 1-xM xCoO 3 (m=Ca,Sr,Ba) cobaltites can be caused by the hole doping and also, independently, by the lattice expansion only induced by an increase of the dopant ion size. The complex pressure effect on ferromagnetic transition T C in cobaltites is well described in terms of competing e g-electron bandwidth W and crystal-field splitting energy, basing on the known pressure variations of the steric factors. For La 1-xBa xCoO 3 with x=0.3,0.5, having a high enough concentration of intermediate spin Co states, we observed a Jahn-Teller-like magnetic transition signified by a distinct hysteresis in field-cooled magnetization below T C. This transition was found to disappear under moderate applied pressure, evidenced for La 0.7Ba 0.3CoO 3 by abrupt changes in the spontaneous magnetization and coercive field at 5 K.

Original languageEnglish
Article number064414
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume83
Issue number6
DOIs
StatePublished - 11 Feb 2011

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