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Magnetic contribution to heat capacity and entropy of nickel ferrite (NiFe 2O 4)

Ziemniak, S.E. ; Anovitz, L.M. ; Castelli, R.A. ; Porter, W.D.

The Journal of physics and chemistry of solids, 2007, Vol.68 (1), p.10-21 [Periódico revisado por pares]

Oxford: Elsevier Ltd

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Título:
Magnetic contribution to heat capacity and entropy of nickel ferrite (NiFe 2O 4)
Autor: Ziemniak, S.E. ; Anovitz, L.M. ; Castelli, R.A. ; Porter, W.D.
Assuntos: A. Magnetic materials ; A. Oxides ; C. Differential scanning calorimetry (DSC) ; Condensed matter: electronic structure, electrical, magnetic, and optical properties ; Critical-point effects, specific heats, short-range order ; D. Magnetic properties ; D. Specific heat ; Exact sciences and technology ; Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.) ; Magnetic properties and materials ; Magnetically ordered materials: other intrinsic properties ; Physics ; Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
É parte de: The Journal of physics and chemistry of solids, 2007, Vol.68 (1), p.10-21
Descrição: The heat capacity of nickel ferrite was measured as a function of temperature from 50 to 1200 °C using a differential scanning calorimeter. A thermal anomaly was observed at 584.9 °C, the expected Curie temperature, T C. The observed behavior was interpreted by recognizing the sum of three contributions: (1) lattice (vibrational), (2) a spin wave (magnetic) component and (3) a λ-transition (antiferromagnetic–paramagnetic transition) at the Curie temperature. The first was modeled using vibrational frequencies derived from an experimentally-based IR absorption spectrum, while the second was modeled using a spin wave analysis that provided a T 3/2 dependency in the low-temperature limit, but incorporated an exchange interaction between cation spins in the octahedral and tetrahedral sites at elevated temperatures, as first suggested by Grimes [15]. The λ-transition was fitted to an Inden-type model which consisted of two truncated power law series in dimensionless temperature ( T/ T C). Exponential equality ( m= n=7) was observed below and above T C, indicating symmetry about the Curie temperature. Application of the methodology to existing heat capacity data for other transition metal ferrites (AFe 2O 4, A=Fe, Co) revealed nearly the same exponential equality, i.e., m= n=5.
Editor: Oxford: Elsevier Ltd
Idioma: Inglês

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Magnetic contribution to heat capacity and entropy of nickel ferrite (NiFe 2O 4)

Ziemniak, S.E. ; Anovitz, L.M. ; Castelli, R.A. ; Porter, W.D.

Oxford: Elsevier Ltd

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