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Journal ArticleDOI

Magnetic Properties of the Dual Oxide System CuO–Fe2O3

01 Jul 1963-Journal of Applied Physics (American Institute of Physics)-Vol. 34, Iss: 7, pp 2093-2096
TL;DR: In this paper, it has been demonstrated that hydrous ferric oxide and cupric oxide gels consist of very small particles and contain magnetically dilute Fe3+ and Cu2+ ions, respectively Heating or aging these gels produces an increase in particle size with the onset of crystalline magnetic interactions.
Abstract: It has been demonstrated that hydrous ferric oxide and cupric oxide gels consist of very small particles and contain magnetically dilute Fe3+ and Cu2+ ions, respectively Heating or aging these gels produces an increase in particle size with the onset of crystalline magnetic interactions Coprecipitated samples of these oxides contain no CuFe2O4 when merely air‐dried or heated at 170°C, but consist of mixtures of CuO and α‐Fe2O3Higher heat‐treatment of these samples up to 900°C results in mixtures of CuFe2O4 and/or α‐Fe2O3 and CuO, with the amount of CuFe2O4 increasing with temperature of heat‐treatment Heat‐treatment at 1100°C produces a solid solution of CuF2O4 and γ‐Fe2O3 in the range greater than 40 mole % Fe2O3 Analysis of the ferrimagnetic magnetization and Curie points suggest that γ‐Fe2O3 has a Curie point of 625°C and a magnetization of 650 emu/g The results are consistent with cationic distribution of Fe[Fe5/3□1/3]O4 and Fe[CuFe]O4
Citations
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Journal ArticleDOI
TL;DR: The physical properties of the system CuFe2O4-Fe3O4 point to the existence of the compound CuFe5O8 as discussed by the authors, and it is concluded that only a little ferrous iron exists even in the region of n-type conductivity, and that the copper within parentheses is predominantly monovalent in the series Cu 1−2x+2(Cu+1Fe+3)xFe 2O4.
Abstract: The physical properties of the system CuFe2O4–Fe3O4 point to the existence of the compound CuFe5O8. The activation energies Ea of quenched specimens exhibit an anomaly at the composition CuFe5O8. The log of the resistivities plotted as a function of composition changes slope, the Curie temperatures Tc display a minimum, and the lattice constants A0 show a maximum at or near this composition.As the iron concentration increases, the Seebeck coefficients θ change from positive to negative at the composition Cu0.55(CuFe)0.225Fe2O4. This is interpreted as being due to the introduction of some ferrous iron at this composition. The equilibrium Cu+1+Fe+3↔Cu+2+Fe+2 lies to the left at least up to this composition. Since the changes in ρ, Ea, A0, and Tc occur at or near the composition CuFe5O8, it is concluded that only a little ferrous iron exists even in the region of n‐type conductivity, and that the copper within parentheses is predominantly monovalent in the series Cu1−2x+2(Cu+1Fe+3)xFe2O4.

26 citations

Journal ArticleDOI
TL;DR: In this article, the crystal structure and magnetization data for slow cooled copper magnesium ferrites with the general formula CuxMg1-xFe2O4 with x = 0.2, 0.4,0.8 and 1 are presented.

9 citations

Dissertation
04 Nov 2011
TL;DR: In this article, a multiferroic compound based on lead iron tungsten PbFe2/3W1/3O3 and lead zirconate PbZrO3 (PZO) oxides is presented.
Abstract: Multiferroics are currently intensely investigated because the coexistence and coupling of ferroic arrangements brings about new physical effects and, for the few room-temperature examples, interesting prospects for applications in various fields. This interest is illustrated by the recent publication of several articles on multiferroics in high impact reviews over the last five years. The main goal of the thesis was to look for new multiferroics by exploiting overlooked and original polar and magnetic arrangements. We more precisely investigated compounds based on lead iron tungsten PbFe2/3W1/3O3 (PFW) and lead zirconate PbZrO3 (PZO) oxides. PFW displays long- and short-range both polar and magnetic orders (ferroelectric-relaxor and antiferromagnetic-spin-glass) while PZO is antiferroelectric with antiferrodistorsivity (oxygen tilts) and existence of ferroelectric instabilities. Combining various techniques from synthesis to electric, magnetic and structural characterizations, we demonstrated that it is possible to get a multiferroic compound (50%PFW-50%PZO) with coexistence of multiple ferroic and structural arrangements with room temperature properties of practical interest. This work opens new prospects in this rich field of multiferroics in peculiar by using antiferroelectrics.

8 citations

Journal ArticleDOI
TL;DR: In this article, a method of measuring the distribution of angles of inclination in mica detectors based on the frequency distribution of areas of fission track entry holes is proposed, and the results of two experiments are presented, and a means of correcting the number of tracks lost during etching is described.
Abstract: The different ways in which minerals and external detectors respond to chemical etching are outlined. While it is prossible that the distribution of angles of inclination of fission tracks in some materials can be determined from the measurement of the aspect ratios of the etch pits this cannot be done using mica detectors. A method of measuring the distribution of angles of inclination in mica detectors based on the frequency distribution of areas of fission track entry holes is proposed. The results of two experiments are presented, and a means of correcting the number of tracks lost during etching is described.

5 citations

Journal ArticleDOI
TL;DR: In this paper, the magnetic parameters such as saturation magnetization, coercive force, remanence ratio, and remanance ratio were measured at 300 and 80 K. The cation distribution has been suggested on the basis of these results.
Abstract: Magnetic parameters such as saturation magnetization (σ s), coercive force (H c), remanence ratio (σ r/σs) etc of CoxMg1−xFe2O4 (0⩽x⩽1) ferrites were measured at 300 and 80 K. The values ofσ s,H c and (σ r/σs) increased as the content of cobalt increased. The magnetic momentμ B was calculated using theσ s data. The cation distribution has been suggested on the basis of these results.

4 citations

References
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Journal ArticleDOI
TL;DR: In this paper, it was shown that a magnetic ion actively participates in ferrimagnetism only if it interacts with two or more magnetic ions in different coordination and that the Curie temperature is determined by the number of complete interactions per active magnetic ion per formula unit.

230 citations

Journal ArticleDOI
TL;DR: In this article, the authors propose a structure quadratique a grand champ coercitif, a saturation magnetique plus faible, and a 1.06-approximation of the temperature.
Abstract: On montre que le ferrite de cuivre prend par refroidissement lent; une structure quadratique a grand champ coercitif, a saturation magnetique plus faible et dont le rapport des axes c/α atteint 1,06. A chaque temperature correspond un etat d'equilibre caracterise par une valeur differente de c/a, comprise entre I et 1,06. L'etude aux rayons X, a l'aide du rayonnement Co K a, montre que les varietes cubiques et quadratiques sont proches de l'etat de ferrite inverse, mais que la fraction λ des ions Fe+++ croit sur les sites tetraedriques au fur et a mesure de la decroissance de la temperature. On propose une surstructure. comportant une repartition ordonnee d'ions de Fe et Cu sur le sous-reseau des places octaedriques. Une telle surstructure, si elle existe, serait tres difficile a mettre en evidence pour les autres ferrites, car les ions de Co, Ni, Mg, etc., deforment moins les reseaux que les ions de Cu++. La variation de c/a aurait alors deux causes, d'une part, l'etablissement d'un ordre entre les ions Cu++ et Fe+++ dans le sous-reseau des sites octaedriques et, d'autre part, la variation de λ, c'est-a-dire les changements de concentration des ions du sous-reseau : on sait en effet que, pour toutes les surstructures, les parametres varient en fonction du titre.

166 citations

Journal ArticleDOI
TL;DR: In this article, it was concluded that the unusual magnetic properties of colloidal nickelous oxide are attributed to the small size of the crystals and the accompanying enhanced specific surface and the decreased number of next nearest magnetic neighbors which results in an altered magnetic environment.
Abstract: Magnetic susceptibility measurements by the Faraday method have been made in the temperature range 4-550\ifmmode^\circ\else\textdegree\fi{}K for a series of iron-free nickelous oxide samples prepared by the heat-treatment of hydrous nickelous hydroxide in a current of nitrogen at temperatures of 250-1300\ifmmode^\circ\else\textdegree\fi{}C, the crystal size as given by electron diffraction methods varying from 80-2000 A. Samples (crystal size \ensuremath{\sim}2000 A) prepared at 1200-1300\ifmmode^\circ\else\textdegree\fi{}C exhibit susceptibilities typical of an antiferromagnetic material, the observed N\'eel point of 523\ifmmode^\circ\else\textdegree\fi{}K agreeing with the results of earlier investigators. In samples (crystal size \ensuremath{\sim}100-200 A) prepared at 300-500\ifmmode^\circ\else\textdegree\fi{}C the susceptibility agrees with that for the larger crystals above the N\'eel point, but exhibit maxima at lower temperatures. The temperatures, ${T}_{c}$, at which the maxima appear, decrease regularly and the amplitudes of the maxima increase regularly, with decreasing crystal size. In the range studied, linear plots [${10}^{\ensuremath{-}4}{T}_{c}=1.090f\ensuremath{-}1.037$] are obtained for ${T}_{c}$ as a function of $f$, the ratio of the average number of next nearest magnetic neighbors per nickel atom to the number of next nearest magnetic neighbors in an infinite crystal, as computed from the observed crystal sizes. Neutron diffraction patterns demonstrate that the magnetic structure is antiferromagnetic at temperatures both above and below ${T}_{c}$, and hence the maxima do not correspond to shifted N\'eel points.The magnetic susceptibility curves for the colloidal crystals of nickelous oxide resemble those obtained by others for certain iron and chromium sulfides. In iron sulfide, $\mathrm{Fe}{\mathrm{S}}_{x}$, the susceptibility increase to the maximum is attributed by N\'eel and others to a ferrimagnetic structure, analogous to certain ferrites. In view of the "active" oxygen (Bunsen test) contents of the nickelous oxide samples which vary from 0.36 to 0.00% as the crystal size increases from 80 to 2000 A, it is possible to attribute the ferrimagnetic behavior to the ordering of a sublattice of defects, as N\'eel does for $\mathrm{Fe}{\mathrm{S}}_{x}$. However, the subsequent decrease in susceptibility at temperatures below ${T}_{c}$ cannot be readily explained for either $\mathrm{Fe}{\mathrm{S}}_{x}$ or NiO.In view of the linear relationship between ${T}_{c}$ and $f$, it is concluded that the unusual magnetic properties of colloidal nickelous oxide is attributable to the small size of the crystals and the accompanying enhanced specific surface and the decreased number of next nearest magnetic neighbors which results in an altered magnetic environment.Nickelous oxide prepared at 250\ifmmode^\circ\else\textdegree\fi{}C contains a small amount of undecomposed nickelous hydroxide detectable by electron diffraction methods. The magnetic susceptibility of pure nickelous hydroxide follows a Curie-Weiss law [${\ensuremath{\chi}}_{m}=\frac{1.07}{(T\ensuremath{-}36)}$] from about 300\ifmmode^\circ\else\textdegree\fi{} to 90\ifmmode^\circ\else\textdegree\fi{}K. Below 90\ifmmode^\circ\else\textdegree\fi{}K, the susceptibility increases more slowly to a value of \ensuremath{\sim}2000\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}6}$ emu at 4\ifmmode^\circ\else\textdegree\fi{}K, and some field dependence was observed, suggesting the desirability of additional studies concerning possible ferromagnetism.

136 citations