摘要:

Recent light scattering experiments probe the surface response of ferromagnets in the regime where both exchange and dipolar interactions are important. We discuss the theory for the response of a semi‐infinite ferromagnet in this region within a continuum theory. We study the spectral density of surface spin fluctuations. This is used to calculate light scattering from spin waves. The light scattering spectra contain features resulting from interactions with both bulk and surface magnons. Our calculations give a good account of the experimental data reported for EuO and Fe.

ISSN:0021-8979    

DOI:10.1063/1.326821

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We report on light scattering measurements on thin polycrystalline samples of iron and nickel. Both the surface and bulk magnons are observed. The measured magnon energies as a function of magnetic field, and of wavevector magnitude and direction, are in good agreement with the calculated values. The predicted exchange induced decay of the surface magnon is observed. In nickel the observed frequencies and linewidths are strongly strain dependent. Oxide layers have an almost negligible effect on the spin wave frequencies in both iron and nickel.

ISSN:0021-8979    

DOI:10.1063/1.326763

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Ni films of a few atomic layers are condensed in UHV at 10 K on metallic substrates of amorphous Pb75Bi25and crystalline Pb, Cu and Bi. Anomalous Hall effect measurements are used to determine the magnetization and the susceptibility of the films. Ni films with a thickness smaller than two atomic layers possess no magnetic moment but show an enhanced susceptibility. Between two and three atomic layers of Ni the susceptibility diverges and thicker films possess a magnetic moment. The experimental results can be well described with a band model of magnetism. A thin Ni film condensed onto a non‐magnetic metal represents a system in which the density of states is changed with thickness, causing a transition from Pauli paramagnetism to band ferromagnetism. In contrast to Ni the ferromagnetic metal Fe possess already for a coverage of 1/6 atomic layer a magnetic moment and shows a paramagnetic behavior.

ISSN:0021-8979    

DOI:10.1063/1.326768

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We report the characterization of two catalysts containing (I) 44 and (II) 57.3 wt. percent of Ni dispersed on Al2O3, containing a graphite binder. It is shown that magnetization (&sgr;) versus H/T curves provide not only an analysis of very small (<100 A˚) catalytically active particles, but also provide clues to the changes in particle profiles (size and shape) during the sintering of Ni dispersions. The conglomeration of the superparamagnetic (single‐domain isotropic) particles to ’’needle’’ shaped (single‐domain anisotropic) particles is analyzed in terms of the corresponding changes in the coercive force. Catalyst (I) with its lower nickel loading was found to be more thermally resistant to the formation of the multidomain particles over the entire HTT range. Work in progress on correlating the electronic parameters of Ni with its catalytic activity is outlined.

ISSN:0021-8979    

DOI:10.1063/1.326770

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Ferromagnetic liquids containing tin‐coated iron particles of 45 A median diameter dispersed in mercury have been prepared electrolytically. After the liquids have been subjected to an abrupt stepwise reduction in an applied magnetic field the magnetization decays with a relaxation time of ∼60 s. Such long decay times cannot be explained if it is assumed that the system consists of separate particles. Long relaxation times of 60 s could arise if the particles form aggregates of approximately 104A diameter which relax by Brownian rotation when the applied field is removed. Further evidence for the the existence of 104A diameter aggregates has been obtained from an analysis of sedimentation and viscosity measurements. However, the possibility that the time dependence is due to conformational changes in the aggregates as the applied field is reduced is not ruled out and is considered a likely alternative explanation.

ISSN:0021-8979    

DOI:10.1063/1.326771

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Iron powders have been produced by the reduction of ferrous ion with borohydride and stabilized by a chromating procedure. The saturation moments is 140 to 160 emu/g. The coercivity can be controlled between 375 and 1150 Oe. Remanence is 0.45 to 0.5 for unoriented powders. The powders are fibers up to 3 &mgr;m long and 1000 A˚ wide consisting of agglomerated spherical crystallites 300 to 450 A˚ in diameter. Chemical analyses show that typical powders contain about 82–85% Fe, 2–3% B, 3% Cr, 5–6% O, and 0.2% H. The moment indicates that only 70% is metallic iron. Measurements up to 100 KG show no superparamagnetic fraction. Fe(OH)2and FeOOH were identified by electron diffraction in some but not all the preparations. Chromating may result in the removal of some non‐magnetic by‐products. Following the chromating treatment, water is removed with methanol. Solvent‐wet powder containing less than 0.1% water can be stored at least 3 months without loss in moment. Cured films of dispersions in a typical epoxy‐type binder lose moment in an accelerated atmosphere test containing SO2and NO2at a rate indicating a lifetime of 10 years in a worst‐case indoor ambient.

ISSN:0021-8979    

DOI:10.1063/1.326772

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The angular dependence of the coercive force and remanence on borohydride reduced iron particles was measured as a function of mulling time. Typically the saturation moment of the powder was 150 emu/gram, while the coercive force and remanence of the unoriented powder was 500 Oe and 0.48, respectively. 50% by weight of the powder was dispersed in an epoxy binder using mulling cycles N=0–300, spread on a polyimide film and oriented in a 2000 Oe field. The remanence in the parallel direction increased from 0.60 for N=0 to 0.74 for N=300. The remanence varied monotonically from a maximum in the parallel (&Vthgr;=0°) to minimum in the perpendicular direction (&Vthgr;=90°). The coercive force (Hc) showed a peak at &Vthgr;=55° and showed a decrease at &Vthgr;=0° and &Vthgr;=90°. The coercive force decreased with mulling cycles and Hc(0°)/Hc(90°) <1. Ball milling the powder produced qualitatively the same results.

ISSN:0021-8979    

DOI:10.1063/1.326773

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

In an earlier publication 1we reported aspects of magnetokinetic studies on the oxidation of FeS2carried out as a function of its particle size (90 to 250&mgr;m) and temperature (400–500 °C); in this study we considered mostly the formation of &agr; and &ggr; Fe2O3. In the present paper we have considered the formation of other oxidation products such as (a) Fe2  (SO4)3, and (b) superparamagnetic particles of &agr; Fe2O3. Mo¨ssbauer spectroscopy has confirmed the presence of (a) and, coupled with X‐ray line broadening studies has shown the absence of (b). The yield of Fe2  (SO4), is found to increase with decreasing starting particle size of FeS2. Using our earlier results 1we have obtained values of (dM/dt) from the initial slopes of the magnetization (M) vs. time curves for particle sizes (180 to 250 &mgr;m). From plots of ln (dM/dt) versus 1/T an activation energy of ∼7 Kcal/mole has been obtained for the following predominant reaction: FeS+(11/4)O2→ (1/2) &agr;Fe2O3+2SO2. This value compares favorably with values reported by other workers2who used classical thermogravimetric analysis.

ISSN:0021-8979    

DOI:10.1063/1.326774

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

After a brief review on the use of spin wave resonance as a tool used to study the magnetic properties of liquid epitaxial garnet layers an example is given for CaGeSmLu:YIG films. A modified melt was used in which the Sm2O3concentration was reduced. The main result is that the growth kinetics produce film growth rate changes that influence the incorporation of Ca and Ge ions. This results in structured layers consisting of a transient and a bulk layer in which the anisotropy fields Ku/M are different. The change of Ku/M of the transient layer during film growth is interpreted in terms of a solid state diffusion process. The results of etch experiments are presented. Also values of the exchange constant A have been measured. Finally, growth conditions are estimated for homogeneous film growth.

ISSN:0021-8979    

DOI:10.1063/1.326775

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

An extensive investigation of eight mixed garnet systems, totally 22 compositions with the samelvalues (0.2&mgr;m), was carried out for realization of high bit density bubble memory chips employing 1.8&mgr;m diameter bubbles in 7&mgr;m‐period devices. The eight systems are YSmLuCaGe, YSmTmCaGe, YEuLuCaGe, YEuTmCaGe, YSmLuGa, YSmTmGa, YEuLuGa and YEuTmGa garnets grown on (111) GGG substrates. In order to fill in the material gap between Sm‐ and Eu‐based garnets, YSmEuLuCaGe and YSmEuTmCaGe garnets were also studied. Comparison was made with respect to static (4&pgr;Ms, Ku, HK, TC, A) and dynamic (&mgr;w, &Vthgr;) properties, as well as Hco1temperature dependence. Q‐factor was varied by changing rare earth content ratio, butland film lattice parameters were left essentially unchanged. From the dynamic and temperature properties viewpoints, it was revealed that YSmLuCaGe, YSmTmCaGe, EuLuCaGe, YSmEuLuCaGe, and YEuTmGa garnet systems are candidate materials, withl=0.2&mgr;m and Q?4, for practical applications which utilize 7&mgr;m‐period patterns.

ISSN:0021-8979    

DOI:10.1063/1.326776

出版商:AIP    

年代:1979

数据来源: AIP