Showing papers on "Superparamagnetism published in 1973"
TL;DR: A natural ferric gel precipitated near freshwater springs has been characterised by X-ray and electron diffraction, thermal, infra-red, magnetic and Mossbauer measurements as discussed by the authors.
98 citations
TL;DR: In this article, the Mossbauer effect was used to study the superparamagnetic behavior of ultrafine Fe 3 O 4 particles as a function of temperature and applied magnetic field.
72 citations
TL;DR: In this article, a soil of Attica (Greece) has been studied by M6ssbauer spectroscopy and magnetization measurements in order to ascertain the nature and form of iron oxides present in it.
Abstract: A soil of Attica (Greece) has been studied by M6ssbauer spectroscopy and magnetization measurements in order to ascertain the nature and form of iron oxides present in it. The room tempera- ture spectra consist of a paramagnetic doublet and a small magnetic sextet. At liquid nitrogen tempera- ture the magnetic component increases considerably at the cost of the paramagnetic component. This behavior is typical of superparamagnetism exhibited by ultrafine magnetic particles. From the values of hyperfine parameters extracted by computer fits of the spectra, the particles can be identified mainly as a-Fe203. The theory of superparamagnetism, in conjunction with M6ssbauer and magnetiza- tion data, is discussed in detail. Application of this theory to the data for the clay fraction of the soil leads to the conclusion that the oxide particles have a size distribution with a mean particle diameter of 131 A and a width of 14 A.
69 citations
TL;DR: In this paper, the superparamagnetic relaxation time for spherical particles with cubic magnetocrystalline anistropy, whose easy axis is either [100] or [111] in zero applied field, was calculated.
Abstract: The superparamagnetic relaxation time is calculated for spherical particles with cubic magnetocrystalline anistropy, whose easy axis is either [100] or [111] in zero applied field. Results are reported for relatively small particles only, in which no anomaly is found. It is concluded that the experimentally observed anomaly in this size region must be due to incoherent magnetization reversals.
63 citations
TL;DR: In this paper, the authors used the Mossbauer effect to study the superparamagnetic behavior of fine particles of 69-31 at.% FeNi alloy, and suggested that the central line originates from the super-paramagnetic behaviour of the ferromagnetic or antiferromagnetic fine particles.
Abstract: The Mossbauer effect is used to study the superparamagnetic behavior of fine particles of 69–31 at.% FeNi alloy. The Mossbauer spectrum of the alloy consists of a central single line and a six‐line magnetic hyperfine pattern for fine particles; but the single line disappears for larger particles, which is in disagreement with the previously reported interpretation that the central single line originates from the paramagnetic state of the antiferromagnetic regions in the ferromagnetic alloy. It is suggested that the central line originates from the superparamagnetic behavior of the ferromagnetic or antiferromagnetic fine particles.
22 citations
Journal Article•
TL;DR: In this paper, a magnetocaloric effect in a superparamagnet was studied and it was concluded that the highly dispersed fraction consists essentially of particles of a single one of the phases of the alloy (the weakly magnetic phase (32)' which exhibit superparamagnetic properties also in the original (monocrystalline) specimen.
Abstract: Measurements have been made of the magnetocaloric effect in a superparamagnet. The object of investigation was a highly disperse powder of a ferromagnetic alloy based on the system Fe-Ni-Al. Upon adiabatic switching on of a magnetic field of intensity 10 kOe, the temperature of the specimen rose in the Curie point region by ~ T ~ 0.03°. The results obtained justify the conclusion that the highly dispersed fraction consists essentially of particles of a single one of the phases of the alloy (the weakly magnetic phase (32)' which exhibit superparamagnetic properties also in the original (monocrystalline) specimen.
20 citations
TL;DR: In this article, it was found that olivines oxidize in air at temperatures appreciably lower than previously thought possible, and the kinetics of magnetite production have been studied gravimetrically and magnetically in the temperature range 300°-420°C yielding values for the activation energy typical of binding energies of cations in oxides, showing the characteristic transitions from superparamagnetism to stable monodomain and to the multidomain state.
Abstract: Summary
The oxidation of finely divided (≲ 1000 A) synthetic ferromagnesian olivines (FexMg1-x)2SiO4 has been studied using gravimetric and magnetic techniques It is found that olivines oxidize in air at temperatures appreciably lower than formerly thought possible Magnetite, Fe3O4, is produced at temperatures ≲ 300°C At higher temperatures this oxidizes to haematite, α– Fe2O3 Above 550°C a second spinel phase, magnesium ferrite, MgFe2O4, is produced together with further quantities of haematite
The kinetics of the magnetite production have been studied gravimetrically and magnetically in the temperature range 300°–420°C yielding values for the activation energy (16–19 eV mole–1) typical of binding energies of cations in oxides
The development of CRM at 345°C has been observed in the magnetite, showing the characteristic transitions from superparamagnetism to the stable monodomain and to the multidomain state
11 citations
TL;DR: In this article, superparamagnetism is observed in Ni fine particles prepared by the gas evaporation technique and the observed temperature and magnetic field dependence of the magnetization is explained by taking the magnetic interaction between particles into account.
Abstract: Superparamagnetism is observed in Ni fine particles prepared by the gas evaporation technique. The observed temperature and magnetic field dependence of the magnetization is explained by taking the magnetic interaction between particles into account. The particle sizes deduced from the magnetization agree with those observed in the electron micrographs.
6 citations
TL;DR: A superparamagnetic doublet was found in BiFeO3 by means of the Mossbauer effect as discussed by the authors, which appeared at room temperature as a doublet superimposed upon the normal six-line spectrum.
5 citations
01 Jan 1973
TL;DR: In this article, a brief review of magnetic interactions and atomic structure of borate and silicate base inorganic glasses containing large amounts of iron group ions is presented, including extensive Mossbauer studies, low field magnetic susceptibility measurements, x-ray diffraction studies, magnetic resonance measurements and ultrasonic sound velocity measurements.
Abstract: In this paper is presented a brief review of our stud-ies of magnetic interactions and atomic structure of borate and silicate base inorganic glasses containing large amounts of iron group ions. Several experimental techniques have been employed in this laboratory to study the atomic struc-ture and magnetic properties of alkaliborate glasses con-taining large amounts of iron and aluminosilicate glasses containing large percentages of cobalt and manganese ions. This work includes extensive Mossbauer studies, low field magnetic susceptibility measurements, x-ray diffraction studies, magnetic resonance measurements and ultrasonic sound velocity measurements. Various magnetic behavior; paramagnetic, superparamagnetic, and antiferromagnetic; are exhibited by these glasses, depending on glass composition and the glass preparation procedure.
4 citations
01 Jan 1973
TL;DR: In this paper, the magnetic moment of a glass containing 40 wt% Fe2O3 was measured and it was shown that the superparamagnetic behavior observed above 100°K can be explained by the presence of antiferromagnetic ordered microdomains with a Neel temperature of about 700°K.
Abstract: Measurements of the magnetic moment of a glass containing 40 wt% Fe2O3 indicate that the superparamagnetic behavior observed above 100°K can be explained by the presence of antiferromagnetically ordered microdomains with a Neel temperature of about 700°K. Below 100°K the behavior is not simply superparamagnetic, and a number of the thermal history and other effects observed are similar to those that characterize mictomagnetic spin glasses.
01 Jan 1973
TL;DR: In this paper, two alternative definitions of superparamagnetic cluster were used: (a) a set of impurity atoms each of which is coupled to at least one other by a ferromagnetic first near neighbor (1NN) interaction, and (b) an impurity atom each of the atoms each is coupled ferromagnetically to one another by either a first near neighbour interaction or a second near neighbor interaction.
Abstract: Superparamagnetic clustering has been investigated in FCC and BCC random substitutional alloys of magnetic solutes in nonmagnetic matrices using a Monte Carlo type computer simulation technique. Two alternative definitions of “superparamagnetic cluster” were used:(a) a set of impurity atoms each of which is coupled to at least one other by a ferromagnetic first near neighbor (1NN) interaction; (b) a set of impurity atoms each of which is coupled ferromagnetically to at least one other by either a first near neighbor interaction or a second near neighbor (2NN) interaction. The magnetic susceptibility calculated for clusters using definition b agrees quite well with the experimental susceptibility data for quenched lower concentration (1 at.% ≤ C ≤ 12 at.%) AuFe alloys in the paramagnetic temperature region. This implies ferromagnetic coupling between Fe-Fe first and second near neighbors in AuFe, and supports the validity of the present method in treating superparamagnetic clustering in alloys.
TL;DR: In this article, the spinel phase of partially devitrifled glass obtained by rapid quenching of 0.175 MnO + 0.65 B2O3 melt was studied by DTA and X-ray analyses and the temperature regions of nucleation, crystallization and decompozition of the spinels were established.
Abstract: Crystallization processes of partially devitrifled glass obtained by rapid quenching of 0·175 MnO + 0·175. Fe2O3 + 0·65 B2O3 melt were studied by DTA and X-ray analyses and the temperature regions of nucleation, crystallization and decompozition of the spinel phase were established. The magnetization curves measured between 4·2 and 250 K in magnetic fields up to 42 kOe divided the samples into two groups: the original as cast glass and those annealed below the crystallization temperature, as well as above the decomposition temperature showed essentially paramagnetic behaviour, whereas those annealed closely above the crystallization temperature displayed a spontaneous magnetic moment. The former ones could not be classified as superparamagnetic but the temperature dependence of their susceptibility could be explained by interactions of the antiferromagnetic type. The comparison of lattice parameter and Curie temperature of the latter one with crystalline Mn
x
Fe3-x
O4, system indicated pronounced iron enrichment of the spinel phase formed during heat treatment.
01 Jan 1973
TL;DR: In this article, the results of magnetization and Mossbauer experiments were presented, which gave evidence for superparamagnetism in the quenched face-centered-cubic (γ) phase of the ternary system Fe0.34C0.52V0.14 (Vicalloy II).
Abstract: Although the occurrence of superparamagnetism has been inferred in many binary alloy systems in which one of the alloy components is nonmagnetic (Beck, 1971), relatively few investigations of this phenomenon have been carried out on concentrated ternary alloys. In this report we present the results of magnetization and Mossbauer experiments which give evidence for superparamagnetism in the quenched face-centered-cubic (γ) phase of the ternary system Fe0.34C0.52V0.14 (Vicalloy II). While the magnetization data agree with the limited data of Nesbitt et al. (1967), our more complete study shows clearly that this alloy does not acquire long-range ferromagnetic order, nor does it indicate either antiferromagnetic long-range ordering or mictomagnetic behavior, down to 4.2° K. Our data can best be described as resulting from ferromagnetic clusters in a weakly magnetic lattice.
01 Jan 1973
TL;DR: In this article, the authors reported on the dispersions of iron species (ions, atoms, etc.) in various vitreous silicates and devised novel synthetic methods for controlling the particle size of the magnetic species by "stuffing" them inside some cage structures.
Abstract: Our interest in this area stems from the extensive studies we reported on the dispersions of iron species (ions, atoms, etc.) in various vitreous silicates1,2. One of our objectives in studying superparamagnetic systems has been to devise novel synthetic methods for controlling the particle size of the magnetic species by “stuffing” them inside some cage structures.