Ernst Schloemann

Epitaxial Fe films on GaAs for hybrid semiconductor‐magnetic memories

The magnetic and structural properties of Fe films deposited by ion‐beam sputtering (IBS) on (100)‐oriented GaAs substrates are described. The films are between 30 and 600 nm thick and are characterized by a coercive field of approximately 3–6 Oe. The saturation magnetization and anisotropy field, inferred from vibrating sample magnetometer measurements agree substantially with the values expected for bulk Fe. Films deposited on the (100) substrate show the expected fourfold (or ‘‘biaxial’’) symmetry with no indication of a uniaxial anisotropy component. These properties make the films ideally suitable for the intended application in a hybrid semiconductor‐magnetic memory, in which two magnetic remanent states with mutually orthogonal magnetization directions interact with an electronic flip‐flop circuit.

Epitaxial Fe films on (100)GaAs substrates by ion beam sputtering

We report the successful growth of single‐crystal Fe films on GaAs substrates in (100) orientation by ion beam sputtering. Magnetic measurements show that the crystalline anisotropy field of these films is substantially the same as that of bulk single crystals.

Eddy-current techniques for segregating nonferrous metals from waste

Abstract Eddy-current separation techniques can play a useful role in processing and beneficiating many types of waste. The physical principles of this method are reviewed with emphasis on techniques using permanent magnets. The techniques have been applied to municipal solid waste, automobile scrap, glass cullet, polyester bottle scrap and electric-cable scrap. Test data for each of these applications are summarized.

In‐plane magnetized YIG substrates self‐biased by SmCo based sputtered film coatings

Highly anisotropic SmCo based films with the TbCu7‐type structure have been sputter deposited directly onto YIG substrates. The SmCo crystallites have the c axes approximately randomly splayed about the substrate plane such that the easy direction of magnetization of the SmCo film is in the film plane. The in‐plane static energy product of the SmCo film layers was about 16 MG Oe. In‐plane vibrating sample magnetometer hysteresis loops of the SmCo film and YIG substrate exhibit a composite form with the YIG field reversal shifted into the first quadrant by the looping field from the SmCo film layer. Approximately 4×4 mm2 pieces of YIG substrate have been measured to determine the YIG bias field and field required for reverse saturation of the YIG as a function of the SmCo based film layer thickness to YIG substrate thickness. It is observed that for SmCo to YIG thickness ratios greater than 0.22, the looping field from the SmCo film layer is sufficient to saturate the YIG magnetization in the reverse direc...

Magnetic resonance experiments on ion beam sputtered {100} Fe films

Ferromagnetic resonance (FMR) measurements have been performed on single‐crystal Fe films, produced by ion beam sputtering techniques on GaAs substrates. In‐plane FMR results over the frequency range 0.1–20.0 GHz were obtained by a slot line technique. The magnetic parameters deduced from these measurements are comparable to bulk Fe. In‐plane angular variation reveals a negligible uniaxial anisotropy contribution to the magnetic anisotropy energy. Spin‐wave excitations were observed in 9.5‐GHz cavity measurements, and are found to obey the n2 law. The exchange stiffness constant is found to be somewhat larger than seen in other epitaxial Fe films. These results show that epitaxial Fe/GaAs films possessing good magnetic properties may be produced by ion beam sputtering techniques.

Theory of low-field loss in partially magnetized ferrites

where and + j K are the diagonal and off-diagonal elements of the loci1 pemeability tensor and I is the normalized dc maqnetization of the partially magnetized ferrite (-1 I < 1). This equation can be tested experimentally by measuring the propagation characteristics of a microstrip line on a ferrite platelet, with a magnetic field applied normal to the platelet. The propagation constant for such a transmission line is (approximately) given by

Instrinsic low-field loss in microwave ferrites

The off-resonance damping parameter due to the three-magnon splitting process is calculated by extending the theory of intrinsic magnetic relaxation processes. The imaginary part of the diagonal component of the microwave permeability tensor is found to decrease with increasing internal magnetic field and to be proportional to the absolute temperature. In magnitude it is somewhat smaller than the subthreshold absorption under parallel pumping, which has a similar physical origin and has previously been calculated and verified by experiments. Since the calculated magnetic damping occurs in all magnetic materials, it is expected to contribute significantly to the insertion loss of many ferrite microwave devices.

A compact broadband microstrip circulator for phased array antenna modules

Minimal size, weight, and cost are three requirements for circulators to be packaged in T/R (transmit/receive) modules. The authors describe circulators realized under these constraints. Hybrid fabrication methods are used in order to meet magnetic biasing and shielding requirements. The circulators described are thought to be near the ultimate in miniaturization for the level of performance achieved over the 6-18-GHz frequency band.<<ETX>>

Low-field loss in ferrites-relevance to broadband circulator design

The criteria for selecting ferrite materials for broadband circulator applications are discussed. Transmission measurements in a circulator-like microstrip fixture are used to select materials for applications in a given frequency band. Data concerning the frequency dependence of transmission loss in the partially magnetized state at various values of bias field are presented. >

Lumped-element circulator optimization

A detailed theoretical model for lumped-element circulators is used as the basis for a synthesis procedure in which the various circuit parameters are determined so that the lossless three-port junction is a perfect circulator at the desired design frequency with maximum bandwidth for a given size of the ferrite disk. Theoretical expressions for the internal and external permeabilities are derived from the Landau-Lifshitz equations. The y-connected lumped-element circulator is then analyzed on the basis of a very general equivalent circuit, which applies to ferrite samples of arbitrary spheroidal shape. Theoretical expressions for the impedance matrix of the ferrite-loaded junction are derived, and the scattering matrix is calculated. An algorithm for finding consistent sets of parameter values that will result in perfect circulation (in the lossless case) at any desired design frequency is used. Optimization for maximal bandwidth at given design frequency is obtained by imposing the additional constraint that the frequency derivatives of the phases of the eigenvalues of the scattering matrix are equal at the design frequency. Sample results are provided that demonstrate the validity of the approach.<<ETX>>