Klaus Schröder

Magnetic Properties of Amorphous Fex Gdy Alloy Thin Films

The magnetism of pure iron and gadolinium films, and of Fex Gdy alloy thin films with 15 to 94 at.% iron prepared by codeposition on a cold (77 °K) substrate were measured at 77 °K and at room temperature. All the alloys had an amorphous structure that was stable to room temperature. The amorphous alloys were found to be ferrimagnetic. The magnitude of the magnetization in rare‐earth transition‐metal alloys does not appear to be structure sensitive since the magnetization of the amorphous alloys follows a linear concentration dependence calculated from an antiparallel coupling of the magnetic moments of crystalline iron and gadolinium.

The magnetic barkhausen effect

Abstract When the magnetization of a ferromagnet (in this paper “ferromagnet” will often include “fernmagnet”) is changed under the influence of an applied magnetic field, the magnetization, particularly in the vicinity of the coercive force, is not smooth function of the field but rather shows a structure composed of many individual steps. This structure is evidence of irreversible changes in magnetization and is known as the barkhausen effect. The effect was named after its discoverer who, in 1919, connected a coil surrounding a ferromagnet to a newly invented amplifier and listened to the output of the amplifier with earphones.1

Stress operated random access, high‐speed magnetic memory

The memory consists of a checkerboard pattern of transducers. Each transducer is connected to two lines of electrical conductors which form two grids of parallel lines. The grids are placed perpendicular to each other. A magnetic block is placed on top of each transducer. A magnetic field is applied to the system of magnetic blocks. It is slightly smaller than the coercive field H(c). One transducer generates a stress wave which will travel into the magnetic block adjacent to it. Its dipoles will line up parallel to the applied field if the stress is high enough. This corresponds to the writing process. If a stress wave interacts with a magnetic block which is magnetized antiparallel to the applied field, the block will reverse its magnetization direction. This leads to stress waves, which will induce a voltage in the transducer. No magnetic energy release and no generation of new stress waves is expected if the field is applied parallel to the magnetization direction of the block. This is the readout pro...

Thermoelectric Power and Electrical Resistance of Chromium‐Iron Alloys from 125° to 625°K

The Seebeck coefficient S of alloys with up to 23 at. % iron has been measured from 125° to 625°K. S of alloys with 10, 15, 19, and 23 at. % Fe was nearly temperature‐independent and had values between 6 and 9 μV/°K. Pure chromium and alloys with up to 4 at. % Fe had a nearly temperature‐independent S at temperatures above 375°K, with S ranging from 13 to 16 μV/°K. However, S exhibited a pronounced maximum below room temperature. The maximum values and the corresponding temperatures are: pure chromium: 21 μV/°K, 275°K; 1 at. % Fe: 27 μV/°K, 240°K; 2 at. % Fe: 40 μV/°K, 175°K; 4 at. % Fe: 34 μV/°K, 280°K. The resistance anomaly of chromium rich samples with maxima below room temperature was similar to that found by other authors. This anomaly has been attributed to the transition to antiferromagnetism.It has been shown that the peak of the phonon drag term S (phon) in pure chromium occurs at 25°K. The observed peaks in our experiments above 125°K should be due to the electron‐diffusion term S (diff). It ca...

Fabricating magnetic Co‐Ni‐C thin‐film alloys by organometallic chemical vapor deposition

We have deposited CoxNiy‐C films with a variety of compositions to verify dependence of the saturation magnetization on the composition. These experiments suggest that we can produce CoxNiy‐C films with a variety of magnetic properties. The CoxNiy‐C films were fabricated by ultraviolet decomposition of cobaltocene and nickelocene. We demonstrated that the photolytic decomposition of these metallocenes produces cyclopentadienyl (C5H5) species, consistent with recent studies of the energetics of the ligand metal bonds.

Hall-effect and resistivity measurements at room temperature and −165°C on chromium-nickel alloys

Abstract The Hall-coefficient R H and the electrical resistivity of Cr-Ni alloys was measured at room temperature and −165°C. An alloy with 3.6 at. % Ni showed at −165°C the highest R H value. It was found that the R H values of Cr-Ni alloys were similar to those found for Cr-Fe alloys, if plotted as a function of electron concentration.

Influence of deposition rates and thickness on the electrical resistivity and thermoelectric power of thin iron films

Abstract The electrical resistance and the thermopower of thin iron films were measured near room temperature as a function of deposition rate and thickness. The films were deposited on glass plates in a high vacuum system at pressures in the region of 10 -7 Torr. Deviations of the resistivity and the Seebeck coefficient from bulk values increased with decreasing deposition rates.

Cu-Pb-Sn Ternary System: Low Cu Additions to Pb-Sn- Binary System

A portion of the Cu-Pb-Sn ternary diagram was determined experimentally. The investigation was concentrated on the high Pb corner and, to a lesser extent of alloys from Sn to the binary Pb-Sn eutectic. The experimental techniques used were thermal analysis, metallography, and electron microprobe analysis. A new technique for determining liquidus temperatures was used. For the high Pb region the proposed ternary eutectic at 0.06 Cu 0.02% SnPb (all compositions are in weight %) was not observed. For most alloys the primary crystallization phase was Cu 3 Sn. It was shown that Cu 6 Sn 5 exists in the solid state; for high Sn alloys, it was observed that the addition of Pb reduced the decomposition temperature of Cu 6 Sn 5 . A ternary eutectic reaction near the binary Pb-Sn eutectic was confirmed, and the temperature of the ternary eutectic was 1°K below that of the binary eutectic. Liquidus temperatures as well as other reactions detected by thermal analysis will be presented.

Determination of energy changes in Cr Fe alloys by antiferromagnetic ordering from resistivity and Seebeck coefficient measurements

Abstract The resistance and Seebeck anomaly of Cr and Cr rich alloys, associated with antiferromagnetic ordering has been related to the formation of an energy gap in the electronic band structure.

MAGNETIC BARKHAUSEN EFFECT AND ITS APPLICATION

Recent developments in the field of Barkhausen signal measurements are reviewed. New highly sensitive measurements are discussed. Stress-induced Barkhausen jumps and recent applications in the field of nondestructive and destructive testing are evaluated.