Showing papers on "Magnetic domain published in 1982"

Diluted magnetic semiconductors: An interface of semiconductor physics and magnetism (invited)

Abstract: This paper reviews the electrical, magnetic, and optical properties of diluted magnetic semiconductors (sometimes also referred to as ‘‘semimagnetic’’ semiconductors). These materials are ternary semiconductor alloys whose lattice is made up in part of substitutional magnetic ions. Cd1−xMnxTe and Hg1−xMnxTe are examples of such systems. As semiconductors, these alloys display interesting and important properties, such as the variation of the energy gap and of effective mass with composition. They also exhibit magnetic properties which are interesting in their own right, e.g., a low temperature spin glass transition and magnon excitations. Most importantly, however, the presence of substitutional magnetic ions in these alloys leads to spin–spin exchange interaction between the localized magnetic moments and the band electrons. This in turn has rather important consequences on band structure and on donor and acceptor states, leading to dramatic effects in quantum transport, impurity conduction, and magneto‐optics. Specifically, the presence of exchange interaction results in extremely large and temperature dependent g‐factors of electrons and holes; in gigantic values of Faraday rotation; in anomalously large negative magnetoresistance; and in the formation of the bound magnetic polaron.

Electron tunneling between ferromagnetic films

Abstract: Spin-polarized tunneling of electrons through Ni-NiO-Ni, Co, and Fe junctions is discussed. The hysteresis of the tunneling resistance in a magnetic field originates in the magnetization process and demonstrates a new interplay of electronic and magnetic properties in ferromagnetic metals.

Properties of Ba ferrite particles for perpendicular magnetic recording media

Abstract: Fine Ba ferrite particles, suitable for coated perpendicular magnetic recording media, have been prepared. The particles, about 0.08 μm in average diameter, are thin hexagonal platelets with easy magnetization axes normal to their planes. Coercivity H c is controllable in a wide range, without significant reduction in magnetization, by Co and Ti substitution. The measured temperature dependences of H c and σ s showed stable characteristics. Good squareness ratio was obtained from an orientation capability measurement.

Perpendicular magnetization structure of Co-Cr films

Abstract: In a perpendicular recording system, a Co-Cr film as a medium is capable of storing very high density signals. Lorentz microscopy of 1000 kV TEM was used to observe the structure of recorded magnetizations in Co-Cr films having perpendicular anisotropy. A composite medium of a Co-Cr film with a soft magnetic back layer was shown by Lorentz microscopy to have a horseshoe magnetization structure. The stable antiparallel magnetization of transition in the Co-Cr layer determined the head-on magnetization structure of the soft magnetic back layer, which consists of a new straw-rope domain structure. The perpendicular magnetization structure of the Co-Cr film was found to consist of small domains magnetized through the film thickness which correspond to the columnar microstructure of the film. Since the intrinsic hysteresis loop of a Co-Cr film was shown to essentially have an ideal rectangular shape, it can be concluded that the Co-Cr layer of a composite film can be recorded by an ideal magnetizing process with negligible demagnetizing field at the transition.

Magnetic Properties of Microcrystals Studied by Mössbauer Spectroscopy

Abstract: The magnetic properties of microcrystals are discussed on the basis of results obtained by use of M?ssbauer spectroscopy. Spectra of microcrystals with dimensions smaller than about 100 A are influenced by magnetic fluctuation effects such as superparamagnetic relaxation and collective magnetic excitations, and these effects allow a determination of the product of the particle size and the magnetic anisotropy energy constant. Measurements on ferromagnetic and ferrimagnetic particles as a function of applied magnetic fields allow a determination of the particle volume. The anisotropy energy constants of microcrystals of Fe, Co, Ni and Fe3O4 are found to change upon chemisorption. Spectra of small particles at low temperatures also give information on the magnetic properties of the atoms in the surface layer. These studies as well as thin film studies show that no magnetically dead layers are present at the surface of the samples. In the case of metallic iron an enhanced magnetic hyperfine field is found, in agreement with theoretical results.

Hexagonal Ferrites from Melts and Aqueous Solutions, Magnetic Recording Materials

Abstract: Owing to their particular crystallographic properties, ferrimagnetic hexagonal ferrites exhibit a far greater coercive force than the conventional magnetic pigments. They therefore appear to be suitable for use in magnetic information storage procedures, some of which are novel and are at the development stage. Thus, magnetic tapes of high coercive force containing barium ferrite could be used as master tapes for copying magnetic information or for producing forgery-proof magnetic cards, if magnetic heads having high-order write fields were successfully developed. Moreover, platelet-like ferrite pigments in which the preferred direction of magnetic orientation is perpendicular to the plane of the platelet are of great interest for perpendicular magnetic recording. In this progress report, the crystal structures, magnetic characteristics of hexagonal ferrites, and chemical processes for their production are discussed. In particular, reactions in salt melts or under hydrothermal conditions produce finely divided pigments whose particles have a pronounced hexagonal, plate-like habit, a narrow particle size distribution, and advantageous magnetic properties. The magnetic properties of the pigments crystallized from salt melts may be adjusted by cation exchange.

Characteristics of RF-sputtered CoCr films

Abstract: The magnetization of the CoCr recording medium has been investigated by several methods. First the perpendicular hysteresis loops are analysed in the thickness range from 500 to 20,000 A. This provided evidence that the magnetization process is typefied by domain wall motion. Second the dependence of the coercivity on the film thickness has been determined. The dependence found can be explained if it is assumed, that the coercivity is caused by domain walls, impeded by the crystallite boundaries. Finally stand-still recording experiments have been performed, which confirm that magnetization takes place by the displacement of domain walls. The switching criterion in the writing process is best met by taking the field averaged over the film thickness.

A study of magnetic hardening in Sm(Co0.69Fe0.22Cu0.07Zr0.02)7.22

Abstract: Magnetic hardening has been examined in the commercial Sm(Co, Fe, Cu, Zr)7.22 permanent magnet by correlating the magnetic properties with the microstructure of the sample. The shape of the initial magnetization curve and magnetic domain observations indicate that there is more than one magnetic hardening process involved in this magnet. This is consistent with microstructure studies which show the existence of nonmagnetic Cu‐rich precipitates and 1:5 phase lamellae distributed in a 2:17 rhombohedral matrix. The presence of the lower Tc 1:5 ferromagnetic phase in the higher Tc 2:17 phase is responsible for the peak observed in the M(T) curve around 870 K and in the change of slope in the Hc(T) curve around 800 K.

Ferromagnetic to Antiferromagnetic Transition in Hf 0.8 Ta 0.2 Fe 2

Abstract: From the magnetization and Mossbauer measurement it was found that the magnetic state of intermetallic compound Hf 0.8 Ta 0.2 Fe 2 is ferromagnetic below 150 K and antiferromagnetic between 150 and 338 K. Above 150 K a phase transition from antiferromagnetic to ferromagnetic state is induced by an external magnetic field and the magnetization curve shows a hysteresis. The result is consistent with that of the recent theoretical study by Moriya and Usami on the coexistence of ferro- and antiferromagnetism in itinerant electron system.

Equation of motion of a spin vortex in a two‐dimensional planar magnet

Abstract: An equation of motion for a spin vortex in a two‐dimensional easy plane magnet is presented and discussed. The theory is based on earlier work on the dynamics of magnetic domains and includes the effects of vortex‐vortex interactions, (weak) applied fields, and dissipation. A possible approach to detecting vortices is also discussed.

A CCD image sensor and a microcomputer make magnetic domain observation clear and convenient

Abstract: Laborious surface polishing has been inevitably necessary for domain observations of bulk magnetic materials by Kerr effect. We have made it possible to observe the magnetic domain without any surface polishing for bulk magnetic materials. A CCD (charge coupled device) image sensor and a microcomputer did the contrast enhancement and noise reduction. Domains in rapidly quenched amorphous magnetic materials have been observed clearly without any surface polishing.

Static and dynamic magnetic studies of compositionally modulated thin films

Abstract: New data on the magnetic behavior of compositionally modulated Pd‐Ni and Cu‐Ni thin films are presented The room temperature magnetization density (M) and first‐order uniaxially anisotropy constant (K) were determined by using a torque magnetometer The temperature dependence of K was obtained from ferromagnetic resonance experiments For the Cu‐Ni system measurements were also performed on a SQUID magnetometer and the results of the three experiments were in agreement It was found that, for the Pd‐Ni system, the moment per Ni‐atom for different films with various asymmetric wavelengths may exceed that of pure Ni, in contrast to the Cu‐Ni films For the later ones it is shown that, when ∼3 atomic planes of Ni are isolated between ∼6 Cu planes, the ferromagnetic behaves as a two‐dimensional ferromagnetic

Large stable magnetic domains

Abstract: Large, thin‐film single domain areas have been observed, in the absence of a bias field, in garnets with magnetization perpendicular to the film plane.1,2 The domain stability in the work by Krumme1 was attributed to a combination of low saturation magnetization and a low Curie temperature. Uchishiba2 relates the stability in his double layer system to appropriate anisotropy fields in one layer compared to the magnetization in the other layer. A more complete model for large domain stability in a bias field free environment is given in this work. Three distinct stability regimes are predicted by the model and all have been observed experimentally. Areas 3.5‐cm in diameter have been made into stable single domains. This was achieved in a material showing a zero bias strip width of 4.5 μm. The single domain diameter was, therefore, 7500 times the equilibrium energy domain width. The technique developed and the model have led to a new means for observing magnetic defects. More importantly, it also offers a means for measuring the strength of the defects. Possible applications of the model are also discussed.

The microstructure and magnetic properties of electroplated cobalt film for perpendicular magnetic recording

Abstract: In this work, the results of a systematic study of the correlation between the microstructure and magnetic hysteretic properties of electroplated Co films [1] are reported. Based on this study, the origin of the perpendicular easy magnetization in the film is confirmed to be associated with the combined effects of crytalline and shape anisotropy of the Co particles in the film. The variations of the demagnetizing field, H d , and coercivity, H c , which would affect the application of the film in perpendicular magnetic recording are also demonstrated by manipulating the interparticle separation through systematic changes in the plating parameters and the post plating treatments.

Magnetic domains in rare-earth cobalt permanent magnets

Abstract: The microstructure of two commercial 2:17 precipitation hardened rare-earth magnets has been examined and compared with the magnetic properties. Transmission electron microscope studies on Sm(Co,Fe,Cu,Hf) 7.25 , Hicorex 99C show a fine cellular microstructure with 2:17 rhombohedral cells surrounded by coherent 1:5 hexagonal cell boundaries. In Sm(Co,Fe,Cu,Zr) 7.22 , TDK REC-26 the cells are much coarser and 1:3 phase thin lamellae are superimposed on the cellular structure. X-ray energy dispersive analysis shows a higher Cu content in the cell boundaries. Lorentz electron microscopy shows "wavy" domain walls in both cases indicating that the domain walls are pinned at the cell boundaries. The higher Cu content of the cell boundaries dilutes the magnetic properties of the SmCo 5 phase and produces a large domain wall energy gradient across the cell boundary leading to the observed high coercivities.

Wall clusters and domain structure conversions

Abstract: The significance of wall clusters, which is a new concept in the theory of soft magnetic materials, is experimentally demonstrated in thin Permalloy configurations. The wall cluster is a collection of domain walls that have one intersection line in common. The transformation of the domain structures takes place through a coherent movement of the domain walls. The correlation between the walls is especially dominant at the intersection line of the walls, called the cluster knot. Relations for the mutual positions of the walls in the wall clusters of great practical relevance are derived explicitly and verified experimentally. The domain structure is formed by the concatenation of wall clusters. The clock sense of the rotation over the walls in the clusters determine which walls of two clusters are linked during the formation of the domain structure. The creation of new clusters takes place through the unfolding of the walls of the clusters which originally coincide with the so-called creation line. As is demonstrated fully, the application of these ideas improves the insight into the complex process of domain structure transformations.

A model of anisotropic Alnico magnets for field computation

Abstract: The modeling of an anistropic Alnico magnet for the purpose of field computation involves assigning a value for the material's permeability in the transverse direction. This is generally based upon the preferred direction properties, being all that are easily available. By analyzing the rotation of intrinsic magnetization due to the self-demagnetizing field, it is shown that the common assumptions relating the transverse to the preferred direction are not accurate. Transverse magnetization characteristics are needed, and these are given for Alnico 5, 5-7, and 8 magnets, yielding appropriate permeability values.

Magnetoresistive sensor having a closed domain structure and electrode biasing

Abstract: A magnetoelectric conversion element comprises a magnetoresistive effect material having a closed domain structure, a pair of contacts for supply of current flowing through the magnetoresistive effect material, and a bias electrode disposed between the contacts for biasing the direction of the current flow. The bias electrode is disposed so that the respective angles of intersection between the directions of current flow through different magnetic domains of the magnetoresistive effect material biased by the bias electrode and the directions of spontaneous magnetization biased by an external magnetic field are both increased or decreased.

Measurements of the complete magnetic moment vector in single crystals of PrAl 2 and NdAl 2

Abstract: Magnetisation measurements parallel and perpendicular to the applied field are reported for single crystals of ferromagnetic NdAl2 and PrAl2 in the range 4.2-200K and for magnetic fields up to 8.00 T applied in the (100) direction and directions near to (110) and (111). A quantitative description of the magnetisation is given in terms of a two-dimensional molecular field theory using two crystal-field parameters and the molecular field constant. Below the Curie temperature a satisfactory agreement between theory and experiment is obtained.

Magnetic domain structures and domain walls in iron fine particles

Abstract: In order to estimate the critical particle size lc for a single domain structure, the magnetic energy densities of an iron fine particle are calculated as a function of the particle size for various configurations of magnetization It is assumed in this calculation that in a small particle the energy of a domain wall consists of the exchange, anisotropy, and magnetic stray field energies It is found that lc is 20 nm for a particle with an axial ratio of n = 1, increases with an increase in n, and is 60 nm for a particle with n = 10 The wall energy of a fine particle is found to be much larger than that of bulk material owing to the stray field energy Due to this wall energy, the magnetization configuration is the circular configuration of spins for the particle with a size larger than lc , and it becomes the flux closure configuration by four domains for the particle with a size larger than 900 nm if n = 1 and 600 nm if n = 10

Domain structures and stress distributions due to ball-point scratching in 3% Si-Fe single crystals with orientation near

Abstract: To determine a stress distribution due to ball-point scratching, we have observed, using a scanning electron microscope, domain structures on the top and bottom surfaces at 3% Si-Fe single crystals with orientation near