Phase diagram of the ( Pr 1 − y Sm y ) 0.7 Ca 0.3 Co O 3 system: Valence and spin state transition versus ferromagnetism
Résumé
The valence and spin-state transition is a very specific transition found in some cobalt oxides which involves a coupled modification in the Co valence and the Co3+ spin state. In the phase diagram of these compounds, one can thus expect a competition of this transition with the ferromagnetism associated with Co4+ low spin/Co3+ high spin double exchange. Here, we study the phase diagram of (Pr1−ySmy)0.7Ca3CoO3 and Pr1−xCaxCoO3 to shed some light on the competition between these two phenomena. To this end, we combine results obtained with a wide variety of techniques: magnetization, heat capacity, resistivity, neutron diffraction, x-ray absorption spectroscopy, and x-ray magnetic circular dichroism. The origin of the various transition lines in the phase diagram of (Pr1−ySmy)0.7Ca3CoO3 as well as that of the critical value ycrit∼0.18 are discussed. Particular attention is paid to the nature of the ground state magnetism which is an issue strongly debated so far in this type of cobaltate.
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REVISED Manuscript With Figures.pdf (1.06 Mo)
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FINAL Supplemental Material.pdf (1.09 Mo)
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