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Title: Magnetic Contribution to Heat Capacity and Entropy of Nicke Ferrite (NiFe2O4)

Abstract

The heat capacity of nickel ferrite was measured as a function of temperature over the range from 50 to 1200 C using a differential scanning calorimeter. A thermal anomaly was observed at 584.9 C, the expected Curie temperature, T{sub 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 {lambda}-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{sup 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 {lambda}-transition was fitted to an Inden-type model which consisted of two truncated power law series in dimensionless temperature (T/T{sub c}). Exponential equality was observed below and above T{sub c}, indicating symmetry about the Curie temperature. Application of the methodology to existing heat capacity data for other transition metal ferrites (AFe{sub 2}O{sub 4}, A = Fe, Co) revealed the same exponential equality, i.e., m = n = 5.

Authors:
Publication Date:
Research Org.:
Knolls Atomic Power Laboratory (KAPL), Niskayuna, NY
Sponsoring Org.:
USDOE
OSTI Identifier:
875901
Report Number(s):
LM-05K177
TRN: US0600951
DOE Contract Number:
DE-AC12-00SN39357
Resource Type:
Conference
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; ABSORPTION; CATIONS; CURIE POINT; ENTROPY; EXCHANGE INTERACTIONS; FERRITE; FERRITES; NICKEL; SPECIFIC HEAT; SPIN WAVES; SYMMETRY; TRANSITION ELEMENTS

Citation Formats

S Ziemniak, L Anovitz, R Castelli. Magnetic Contribution to Heat Capacity and Entropy of Nicke Ferrite (NiFe2O4). United States: N. p., 2005. Web.
S Ziemniak, L Anovitz, R Castelli. Magnetic Contribution to Heat Capacity and Entropy of Nicke Ferrite (NiFe2O4). United States.
S Ziemniak, L Anovitz, R Castelli. Thu . "Magnetic Contribution to Heat Capacity and Entropy of Nicke Ferrite (NiFe2O4)". United States. doi:. https://www.osti.gov/servlets/purl/875901.
@article{osti_875901,
title = {Magnetic Contribution to Heat Capacity and Entropy of Nicke Ferrite (NiFe2O4)},
author = {S Ziemniak, L Anovitz, R Castelli},
abstractNote = {The heat capacity of nickel ferrite was measured as a function of temperature over the range from 50 to 1200 C using a differential scanning calorimeter. A thermal anomaly was observed at 584.9 C, the expected Curie temperature, T{sub 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 {lambda}-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{sup 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 {lambda}-transition was fitted to an Inden-type model which consisted of two truncated power law series in dimensionless temperature (T/T{sub c}). Exponential equality was observed below and above T{sub c}, indicating symmetry about the Curie temperature. Application of the methodology to existing heat capacity data for other transition metal ferrites (AFe{sub 2}O{sub 4}, A = Fe, Co) revealed the same exponential equality, i.e., m = n = 5.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Thu Dec 15 00:00:00 EST 2005},
month = {Thu Dec 15 00:00:00 EST 2005}
}

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  • 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, TC. The observed behavior was interpreted by recognizing the sum of three contributions: (1) lattice (vibrational), (2) a spin wave (magnetic) component and (3) a ?-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 T3/2 dependency in the low-temperature limit,more » but incorporated an exchange interaction between cation spins in the octahedral and tetrahedral sites at elevated temperatures, as first suggested by Grimes [15]. The ?-transition was fitted to an Inden-type model which consisted of two truncated power law series in dimensionless temperature (T/TC). Exponential equality (m=n=7) was observed below and above TC, indicating symmetry about the Curie temperature. Application of the methodology to existing heat capacity data for other transition metal ferrites (AFe2O4, A=Fe, Co) revealed nearly the same exponential equality, i.e., m=n=5.« less
  • A study of the heat capacity and magnetic susceptibility of MgNi/sub 2/ was undertaken to ewn-aluate the report by Voss that this compound is ferromagnetic at temperatures below 235 deg C. The results of the investigation renewal no ewn-idence of ferromagnetism in this Laves phase. MgNi/sub 2/ is found to be a inoderately strongly paramagnetic material with a susceptibility which is practically constant between 25 and 450 deg C. Thermomagnetic analysis shows a very slight but abrupt drop in the suscepiibility at 194 deg C. and heat- capacity ineasurements reveal a wn-ery small thermal anomaly at the same temperature. Themore » effects are thought to be associated with some iype of irregulariiy in the lattice. such as the defect struciure which occurs when a nickel atom replaces a magnesium atom in the MgNi/sub 2/ lattice. Third-Law entropies of MgNi/sub 2/ at temperatures up to 555 deg K are also presented. (auth)« less