Тип публикации: статья из журнала
Год издания: 2008
Идентификатор DOI: 10.1088/0953-8984/20/44/445214
Ключевые слова: Antiferromagnetism, Crystallography, Entropy, Lead alloys, Magnetic materials, Magnetism, Manganese, Manganese compounds, Powders, Single crystals, Specific heat, Spin dynamics, Antiferromagnetic orders, Charge localizations, Entropy losses, Excess heat capacities, Experimental datums, Heat capacities, Magnetic contributions, Magnetic orders, Magnetic states, Magnetic subsystems, Magnetic transitions, Manganese oxides, Nonmagnetic, Spin systems, Temperature curves, Temperature dependences, Temperature intervals, Temperature ranges, Manganese alloys
Аннотация: We present the results of a heat capacity study of Pb(3)Mn(7)O(15) single crystals with approximately equal concentrations of Mn(3+) and Mn(4+) ions. In the temperature interval between 210 and 260 K, an excess heat capacity of nonmagnetic origin, most likely associated with the process of charge localization, has been observed. Also, three pronounced anomalies corresponding to the changes in a magnetic subsystem of the crystal have been observed in the temperature dependence of the heat capacity. A broad hump near 150 K is related to the formation of a short-range magnetic order. This process of short-range ordering is rather prominent, considering the appreciable value of the entropy loss accompanying the change in the magnetic state. A clear lambda-shaped peak at 70 K marks the onset of a long-range antiferromagnetic order. Another anomalous contribution to the heat capacity of magnetic origin has been revealed at temperatures below 20 K. This contribution is associated with a magnetic transition of an unknown nature, which is also clearly evident in magnetization versus temperature curves. The total magnetic contribution to the entropy deduced from the actual experimental data over the entire temperature range is much smaller than is expected for a completely ordered Mn spin system in the crystal. We suggest several possible reasons that may account for this `missing' entropy.
Журнал: JOURNAL OF PHYSICS-CONDENSED MATTER
Выпуск журнала: Vol. 20, Is. 44
ISSN журнала: 09538984
Место издания: BRISTOL
Издатель: IOP PUBLISHING LTD
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