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Title: Thermal effect on magnetic parameters of high-coercivity cobalt ferrite

Abstract

We prepared very high-coercivity cobalt ferrite nanoparticles synthesized by a combustion method and using short-time high-energy mechanical milling to increase strain and the structural defects density. The coercivity (H{sub C}) of the milled sample reached 3.75 kOe—a value almost five times higher than that obtained for the non-milled material (0.76 kOe). To investigate the effect of the temperature on the magnetic behavior of the milled sample, we performed a thermal treatment on the milled sample at 300, 400, and 600 °C for 30 and 180 min. We analyzed the changes in the magnetic behavior of the nanoparticles due to the thermal treatment using the hysteresis curves, Williamson-Hall analysis, and transmission electron microscopy. The thermal treatment at 600 °C causes decreases in the microstructural strain and density of structural defects resulting in a significant decrease in H{sub C}. Furthermore, this thermal treatment increases the size of the nanoparticles and, as a consequence, there is a substantial increase in the saturation magnetization (M{sub S}). The H{sub C} of the samples treated at 600 °C for 30 and 180 min were 2.24 and 1.93 kOe, respectively, and the M{sub S} of these same samples increased from 57 emu/g to 66 and 70 emu/g, respectively. The H{sub C} and the M{submore » S} are less affected by the thermal treatment at 300 and 400 °C.« less

Authors:
; ; ;  [1];  [2];  [3]
  1. Instituto de Física, Universidade Federal de Mato Grosso, 78060-900 Cuiabá-MT (Brazil)
  2. Laboratório Nacional de Nanotecnologia, Centro Nacional de Pesquisa em Energia e Materiais, 13083-970 Campinas (Brazil)
  3. Centro Brasileiro de Pesquisas Físicas, Rua Xavier Sigaud 150 Urca. Rio de Janeiro (Brazil)
Publication Date:
OSTI Identifier:
22308915
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 116; Journal Issue: 3; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 77 NANOSCIENCE AND NANOTECHNOLOGY; COBALT COMPOUNDS; COERCIVE FORCE; COMBUSTION; CRYSTAL DEFECTS; DENSITY; FERRITES; HEAT TREATMENTS; HYSTERESIS; MAGNETIZATION; MICROSTRUCTURE; NANOPARTICLES; SATURATION; STRAINS; TEMPERATURE RANGE 0400-1000 K; TRANSMISSION ELECTRON MICROSCOPY

Citation Formats

Chagas, E. F., E-mail: efchagas@fisica.ufmt.br, Ponce, A. S., Prado, R. J., Silva, G. M., Bettini, J., and Baggio-Saitovitch, E.. Thermal effect on magnetic parameters of high-coercivity cobalt ferrite. United States: N. p., 2014. Web. doi:10.1063/1.4890033.
Chagas, E. F., E-mail: efchagas@fisica.ufmt.br, Ponce, A. S., Prado, R. J., Silva, G. M., Bettini, J., & Baggio-Saitovitch, E.. Thermal effect on magnetic parameters of high-coercivity cobalt ferrite. United States. doi:10.1063/1.4890033.
Chagas, E. F., E-mail: efchagas@fisica.ufmt.br, Ponce, A. S., Prado, R. J., Silva, G. M., Bettini, J., and Baggio-Saitovitch, E.. Mon . "Thermal effect on magnetic parameters of high-coercivity cobalt ferrite". United States. doi:10.1063/1.4890033.
@article{osti_22308915,
title = {Thermal effect on magnetic parameters of high-coercivity cobalt ferrite},
author = {Chagas, E. F., E-mail: efchagas@fisica.ufmt.br and Ponce, A. S. and Prado, R. J. and Silva, G. M. and Bettini, J. and Baggio-Saitovitch, E.},
abstractNote = {We prepared very high-coercivity cobalt ferrite nanoparticles synthesized by a combustion method and using short-time high-energy mechanical milling to increase strain and the structural defects density. The coercivity (H{sub C}) of the milled sample reached 3.75 kOe—a value almost five times higher than that obtained for the non-milled material (0.76 kOe). To investigate the effect of the temperature on the magnetic behavior of the milled sample, we performed a thermal treatment on the milled sample at 300, 400, and 600 °C for 30 and 180 min. We analyzed the changes in the magnetic behavior of the nanoparticles due to the thermal treatment using the hysteresis curves, Williamson-Hall analysis, and transmission electron microscopy. The thermal treatment at 600 °C causes decreases in the microstructural strain and density of structural defects resulting in a significant decrease in H{sub C}. Furthermore, this thermal treatment increases the size of the nanoparticles and, as a consequence, there is a substantial increase in the saturation magnetization (M{sub S}). The H{sub C} of the samples treated at 600 °C for 30 and 180 min were 2.24 and 1.93 kOe, respectively, and the M{sub S} of these same samples increased from 57 emu/g to 66 and 70 emu/g, respectively. The H{sub C} and the M{sub S} are less affected by the thermal treatment at 300 and 400 °C.},
doi = {10.1063/1.4890033},
journal = {Journal of Applied Physics},
number = 3,
volume = 116,
place = {United States},
year = {Mon Jul 21 00:00:00 EDT 2014},
month = {Mon Jul 21 00:00:00 EDT 2014}
}
  • Melt-quenched and thermomechanically deformed samples with the nominal compositions Pr{sub 18}Co{sub 82}, Pr{sub 18}Co{sub 81}C, and Pr{sub 18}Co{sub 76}C{sub 6} were examined with optical and electron microscopy, differential thermal analysis, and superconducting quantum interference device magnetometry that was performed in the temperature range 20 K{le}{ital T}{le}300 K. At room temperature, Pr{sub 18}Co{sub 82} exhibits poor coercivity and remanence, 600 Oe and 2.9 kG, respectively. Pr{sub 18}Co{sub 81}C exhibits relatively superior remanence, 7.7 kG, but poor coercivity, 2.7 kOe, while Pr{sub 18}Co{sub 76}C{sub 6} exhibits the opposite trend, {ital B}{sub {ital R}}=4.5 kG and {ital H}{sub {ital ci}}=12 kOe. The mainmore » phase present in all samples, PrCo{sub 5}, has basically the same character and morphology for all three samples and shows no evidence of intragranular carbon, which is demonstrated to reside in the impurity phases. The superior coercivity found in Pr{sub 18}Co{sub 76}C{sub 6} is attributed to a previously unknown triclinic phase, Pr{sub 3}Co{sub 4}C{sub {ital x}} ({ital x}{approx_equal}3{endash}4) that appears to undergo a magnetic{endash}nonmagnetic transition with increasing temperature around {ital T}=80 K. The variety of magnetic properties exhibited by each sample is due to the variety of minor phases present in each sample, which may be a product of the effect that carbon has on the solidification rate of the parent alloy. {copyright} {ital 1996 American Institute of Physics.}« less
  • The effects of deviation from stoichiometric composition on the structural and magnetic properties of cobalt ferrite, Co{sub x}Fe{sub 3-x}O{sub 4} (x = 0.2 to 1.0), are presented. Both CoFe{sub 2}O{sub 4} and Fe{sub 3}O{sub 4} have a spinel crystal structure, and it might be expected that intermediate compositions would have the same structure. However, results show that synthesis via the ceramic method leads to the development of a secondary {alpha}-Fe{sub 2}O{sub 3} phase. Both structural and magnetic properties are altered depending on the concentration of the {alpha}-Fe{sub 2}O{sub 3} phase. Saturation magnetization is at a maximum for the stoichiometric compositionmore » (i.e., x = 1.0) and thereafter decreases with x. In attempts to achieve the properties required for application, the ceramic method offers the ability to selectively adjust the concentrations of both CoFe{sub 2}O{sub 4} and {alpha}-Fe{sub 2}O{sub 3} phases.« less
  • We present the influence of deposition pressure on the structural and magnetic properties of cobalt ferrite thin films. Thin films of Co ferrite were deposited by rf sputtering on Si (100) substrate and characterized by X - Ray Diffraction (XRD), Atomic Force Microscopy (AFM) and Vibrating Sample Magnetometer (VSM). The XRD patterns showed the formation of crystalline single phase of the films. The particle size and surface roughness of the films were strongly influence by gas pressure. Hysteresis loops measured at room temperature showed the enhancement of magnetic properties with the increase of gas pressure which is attributed to themore » decrease of particle size.« less
  • Nanocrystalline particulates of Er doped cobalt-ferrites CoFe{sub (2−x)}Er{sub x}O{sub 4} (0 ≤ x ≤ 0.04), were synthesized, using sol-gel assisted autocombustion method. Co-, Fe-, and Er- nitrates were the oxidizers, and malic acid served as a fuel and chelating agent. Calcination (400–600 °C for 4 h) of the precursor powders was followed by sintering (1000 °C for 4 h) and structural and magnetic characterization. X-ray diffraction confirmed the formation of single phase of spinel for the compositions x = 0, 0.01, and 0.02; and for higher compositions an additional orthoferrite phase formed along with the spinel phase. Lattice parameter of the doped cobalt-ferrites was higher than that of pure cobalt-ferrite.more » The observed red shift in the doped cobalt-ferrites indicates the presence of induced strain in the cobalt-ferrite matrix due to large size of the Er{sup +3} compared to Fe{sup +3}. Greater than two-fold increase in coercivity (∼66 kA/m for x = 0.02) was observed in doped cobalt-ferrites compared to CoFe{sub 2}O{sub 4} (∼29 kA/m)« less