Showing papers on "Superparamagnetism published in 1976"
TL;DR: In this article, it was shown that below the superparamagnetic blocking temperature thermally excited oscillations of the magnetization around an energy minimum reduce the average magnetization and the magnetic hyperfine splitting in the Mossbauer spectrum.
Abstract: A simple model is developed to explain the often-observed diminished values of the magnetic hyperfine fields in microcrystals. It is shown that below the superparamagnetic blocking temperature thermally excited oscillations of the magnetization around an energy minimum reduce the average magnetization and the magnetic hyperfine splitting in the Mossbauer spectrum. In a microcrystal of volumeV these quantities are reduced by a factor of about 1−kT/(2κV), wherekT is the thermal energy and κ is related to the anisotropy constant. Mossbauer spectra of 60 A, 100 A, and 120 A Fe3O4 particles and 120 A α-Fe2O3 particles show excellent agreement with the theory.
300 citations
TL;DR: Magnetisation measurements made on the amorphous ferromagnet Metglas 2826-A, (TC = 254.5 K), in the temperature range 4.2 ≤ T ≤ 450 K indicate that it obeys the static scaling law hypothesis over an unusually wide temperature range as mentioned in this paper.
59 citations
Patent•
02 Dec 1976TL;DR: The magnetic behavior of the glass carrier particles which is dependent on the number present and size of the ferrite crystallites can be closely controlled by heat treatment at temperatures in the range of between about 600° C and 800° C.
Abstract: Electrostatographic carrier materials having low bulk densities and high magnetic permeabilities are obtained by providing an alumino-boro-silicate glass particle containing from between about 10 to about 15 molar percent Fe 2 O 3 in which superparamagnetic ferrite crystallites having an average particle size of up to about 500A have been precipitated by heat treatment. The magnetic behavior of the glass carrier particles which is dependent on the number present and size of the ferrite crystallites can be closely controlled by heat treatment at temperatures in the range of between about 600° C and 800° C. When mixed with toner particles, these magnetic glass carrier materials experience significantly reduced toner impaction levels.
40 citations
TL;DR: In this article, a superconducting solenoid with a capacity of up to 100 kOe was used for the calculation of crystallite size distributions from the magnetic data, and a computational technique was developed for this purpose and tests on model distributions carried out.
30 citations
20 citations
TL;DR: In this article, the magnetic domain structure of basalt basalt from leg 37 basement rock was investigated using granulometric techniques and the Lowrie-Fuller test, and the results indicated that magnetite or titanomagnetite was the only significant magnetic carrier present.
Abstract: Magnetic experiments conducted on leg 37 basement rock include granulometric techniques (study of low- and high-field hysteresis and temperature dependence of initial susceptibility and of magnetization) and the Lowrie-Fuller test. On the basis of these experiments the following inferences were made concerning the magnetic domain structure: The effective particle size of only one sample, basalt from hole 332B, is in superparamagnetic size range. The single sample of peridotite (from hole 334) provided the only evidence for the presence of multidomain particles. The behavior of the remaining (44) samples, all basalts, can be interpreted as being due to single domain particles which in some cases appear to be moderately to strongly cation deficient. Magnetite or titanomagnetite was found to be the only significant magnetic carrier present.
18 citations
TL;DR: In this article, the magnetic properties of ternary Fe-Cr-Ni alloys were studied over a range of temperatures from 10 − 300 K by both ac and dc techniques, in fields from 5 A m −1 to 6 MA m − 1.
16 citations
TL;DR: In this article, the coercive force and remanence properties of ferromagnetic fluids with tin and sodium as additives were investigated and good agreement was obtained between the experimental observations and the theoretical form of the coercive forces against particle size curve obtained from a log normal distribution.
Abstract: Ferromagnetic fluids have been prepared by the electrodeposition of iron on to an agitated mercury cathode. The mercury contained additives such as tin and sodium, the presence of which, has been shown to enhance particle stability. The particle sizes are approximately 45A in diameter and fluids stable over many months have now been prepared. Magnetisation measurements have been made at 77K and 293K and the ageing effects of heating the fluids to 420K have been studied over the short and long term. The saturation magnetisation of these samples studied is typically 65 gauss and the fluids are visibly ferromagnetic. Magnetic measurements indicate that all fluids prepared are superparamagnetic at room temperature but possess properties of hysteresis in the solid state at 77K. The coercive force at 77K for those fluids with additives increased less rapidly on ageing than for fluids without additives. For those fluids containing tin and sodium, the coercive force becomes constant within 24 hours at an ageing temperature of 420K. The change in coercive force during ageing is considered to arise from an increase in particle size and the constant value obtained in the fluid containing tin and sodium is interpreted as an indication that particle growth has been inhibited. The magnetic properties are dependent upon the particle size distributions and good agreement is obtained between the experimental observations and the theoretical form of the coercive force against particle size curve obtained from a log normal distribution. Measurements of the coercive force and remanence not only allows the stability of the ferromagnetic fluid to be monitored but also enable predictions to be made concerning the particle size distribution. The results of such measurements on iron particles in mercury with tin and sodium as additives are presented in this paper.
8 citations
TL;DR: In this article, superparamagnetic magnesioferrite particles were precipitated from single-crystal MgO containing 2.2 cation% Fe, by aging between 700° and 1000°C.
Abstract: Superparamagnetic magnesioferrite particles were precipitated from single-crystal MgO containing °2.2 cation% Fe, by aging between 700° and 1000°C. The anisotropy field of the precipitates was measured as a function of aging time and aging temperature. Superparamagnetic analysis was used to calculate the precipitate growth rate for several aging temperatures. It was found that from the earliest times studied, the particles grow according to the law of diffusion-controlled coarsening. An activation energy of 72.5 kcal/mol was calculated for this growth process.
7 citations
TL;DR: In this article, the magnetic properties of the cubic Laves-phase compounds GdCo 2, TbCo 2, DyCo 2 and GdNi 2 have been studied by magnetic analysis.
Abstract: The oxidation of the cubic Laves-phase compounds GdCo 2 , TbCo 2 , DyCo 2 and GdNi 2 has been studied by magnetic analysis. Oxidation was carried out by heating in air at 750 K, but it also takes place at a significant rate in air at S.T.P. The oxidised compounds are superparamagnetic due to the formation of small particles of the transition metal.
4 citations