摘要:

In this paper the first experiment of thermomagnetic writing of a hologram on a thin film of EuO and the reconstruction of the hologram is reported. Writing of the hologram is achieved by using a giant pulsed ruby laser as a source for thermomagnetization. Erasing of the hologram is accomplished by a small applied magnetic field. The ruby laser is used because of its ability to provide the energy required for writing in a time that is short compared with the thermo‐relaxation time. A hologram with shallow angle (10 &mgr; resolution) was recorded and the reconstruction of the hologram was done using a He&sngbnd;Ne laser as a source. The formation of the hologram is based on the fact that the index of refraction of the material is a function of magnetization. Thus, the different state of magnetization induced by the laser pulse acts as a phase‐hologram for polarized light. Polarizing elements were used to observe the reconstructed images from the magnetic holograms. Results were also obtained for the diffraction intensity in the different orders of a simple thermo‐magnetic hologram. An analysis is presented to interpret the observed phenomena and gives the calculated efficiency that can be obtained under ideal conditions.

ISSN:0021-8979    

DOI:10.1063/1.1657805

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Thin cobalt films, with low phosphorous content, electroplated on suitable substrates, at apH of 6–6.5, have useful properties for thermomagnetic recording. They have a room‐temperature coercivity,Hc(25°C) in excess of 200 Oe, Hc(25°C)/Hc(150°C) in excess of 3, and good working margins.

ISSN:0021-8979    

DOI:10.1063/1.1657806

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The fabrication and basic magnetic characteristics of a closed‐flux memory element will be described. The element is made entirely by vacuum deposition and photoetching techniques. The element, which uses oxidized silicon as a substrate, consists of two 0.5‐&mgr; cobalt‐Permalloy films deposited so that they overlap the bit line and provide flux closure in the easy direction. Partial flux closure in the hard direction is obtained by using a 1‐&mgr; ``keeper'' film. Tabs are included on the memory films to help reduce the reluctance through the SiO layer, which insulates the word lines from the bit lines. The problems involved in this development include: obtaining satisfactory insulation from the silicon, raising theHcof the first magnetic film by a suitable undercoat, keeping the dispersion of the second magnetic layer and keeper film low by use of a smoothing coat, keeping the crystal size of the word and bit lines small during subsequent processing by using 95:5 Al&sngbnd;Cu alloy, and interlayer adherence, particularly the keeper layer.

ISSN:0021-8979    

DOI:10.1063/1.1657807

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The dynamic magnetization spread in a uniaxial film sheet excited by a pulse current in a strip line has been investigated by the application of the Landau‐Lifshitz equation for distributed systems. A numerical solution is obtained from two coupled nonlinear integrodifferential equations. The key mechanism responsible for the wide spread of magnetization is: Different speeds in the gyromagnetic precession of spins in regions underneath and outside the strip result in nonuniform magnetization distribution which in turn causes propagation of the magnetization change at high speed (10 &mgr;m/nsec) through magnetostatic and exchange coupling. Direct measurements on the dynamic magnetization distribution are made with a nanosecond microscopic (3 nsec rise time, 25 &mgr;m resolution) Kerr apparatus. Experimental results are in good agreement with analytical predictions.

ISSN:0021-8979    

DOI:10.1063/1.1657808

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

We have used the technique of transmission electron microscopy for the static observation of recorded magnetization patterns in high‐coercivity films of cobalt and iron. Such magnetization patterns consist of a series of oppositely magnetized regions, and are characterized by the length of these magnetized regions and by the spatial variation of the magnetization in the transition regions in which the magnetization reverses from one direction to the opposite direction. Magnetic bit patterns of different wavelengths were recorded with conventional high‐resolution transducers and by magnetic transfer from high‐coercivity masters. The Foucault method using the objective aperture diaphragm was found particularly applicable for observing the oppositely magnetized regions, resulting in good contrast for wavelengths as small as 2 &mgr;. For the observation of the magnetization transition regions, the defocus mode was found better applicable. Measurements of the length of the transition region by this method are in good agreement with our theoretical calculations using harmonic analysis to determine the resulting demagnetization.

ISSN:0021-8979    

DOI:10.1063/1.1657809

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The life expectancy of DRO‐plated wires was studied from various aspects by using an accelerated aging technique. Theoretical predictions regarding annealing processes were made by considering a structural defect model which assumes fixed and rotatable components of anisotropy with different activation energies. The predictions were verified experimentally under various annealing conditions. An extrapolation method to estimate the lifetime at operating temperature was established by adopting the Arrhenius equation. Activation energies were determined by using the rate of decay of output voltage under a worst‐case DRO memory test as a criterion. Three activation energies were evaluated: (1) 1.3 eV for the zero applied field case, (2) 2.4 eV for a 36 Oe hard‐axis field applied, and (3) 0.8 eV for fringing fields off the ends of a solenoid applying the 36‐Oe hard‐axis fields. The shelf life was extrapolated to be 2×106years at 40°C. The dynamic test evaluated the lifetime under environmental conditions using a 256‐bit experimental plane which was exercised, sensed, and data recorded at 150°C and the memory lifetime at operating temperature was determined by extrapolating the above results using the lowest activation energy projection. Therefore, memory working lifetime in DRO mode is estimated to be >100 years at 50°C with no dropouts, and >350 years at 50°C with a 5% dropout occurrence.

ISSN:0021-8979    

DOI:10.1063/1.1657810

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

Methods are described for reducing shot‐noise in magnetic‐film memories which are to be read magneto‐optically with the auxiliary aid of an electron beam. In such memories the principal source of shot noise is from the light which is used to illuminate the memory array. The following methods of reducing array shot noise are considered: (1) selective background, (2) magneto‐optical balance, (3) temperature control of magneto‐optical spectra in rare‐earth iron garnets (REIG). It is concluded that the use of REIG spectra appears to offer not only the best, but also a satisfactory solution to the array shot‐noise problem.

ISSN:0021-8979    

DOI:10.1063/1.1657811

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

We show that, as a consequence of the fact that the Bogoliubov transformation mixes spin waves on different sublattices, the phenomenological Loudon Hamiltonian describing the two spin‐wave absorption in rutile antiferromagnets also predicts a linear Stark effect on the two spin‐wave line in these materials in the presence of dc electric fields. We present calculated line shapes for ir absorption in a dc field. The dc field needed to observe significant effects is of order 106V/cm. The Stark‐effect experiment could be used to measure the parameter of the Loudon Hamiltonian, which is of interest from a theoretical point of view, since some mechanisms of two spin‐wave absorption predict &pgr;2=0. The Stark effect also provides the possibility in principle of producing a phase transition in these antiferromagnets by the application of a dc electric field. This is the case because the shift in the spin‐wave energy produced by the dc field can be negative for some values ofk. We study this possibility in a simple approximation. The required fields are too large to be realizable in rutile antiferromagnets but there is some hope of observing such transitions in other kinds of antiferromagnets.

ISSN:0021-8979    

DOI:10.1063/1.1657812

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The spectra of thin slabs of single‐crystal MnF2and KMnF3at low temperatures have been measured, both in the far infrared (40–360 cm−1) and in the visible (3850–4000 Å). The far infrared spectra consist of many sharp lines superimposed on a broad phonon background. The sharp lines are caused by processes involving the simultaneous creation of as many as 8 magnons, sometimes accompanied by the creation or absorption of standing elastic waves. In the visible spectrum, exciton lines with magnon sidebands are observed, accompanied by many weak satellite lines. The satellite lines correspond to processes in which as many as 30 magnons may be created simultaneously. For both substances, the observed lines in both spectra can be fitted to within experimental accuracy using combinations of only 3 single‐magnon energies.

ISSN:0021-8979    

DOI:10.1063/1.1657813

出版商:AIP    

年代:1969

数据来源: AIP

摘要:

The temperature dependence of the localized magnetic mode associated with cobalt impurities in MnF2has been studied by neutron inelastic scattering methods. The frequency of the localized mode, relative to its value at the lowest temperatures, falls with increasing temperature less rapidly than the sublattice magnetization and also less rapidly than the frequencies of the band modes in the doped crystal. The frequency of the local mode falls from 3.57±0.05(1012Hz) atT/TN=0.06 to 3.12±0.13(1012Hz) atT/TN=0.84. Results have also been obtained for the temperature dependence of the relative intensities of the neutron groups associated with the local and band modes. Molecular field calculations show that the cobalt ion produces an enhancement, at elevated temperatures, of the thermal average value of the spin on neighboring manganese ions over that in the pure material. This leads to a temperature dependence of the local modes smaller than that of the sublattice magnetization, as observed.

ISSN:0021-8979    

DOI:10.1063/1.1657814

出版商:AIP    

年代:1969

数据来源: AIP