Circular Magnetic Domains Research Articles

Novel 'writing' using magnetic force microscopy in ultrahigh vacuum

Circular magnetic domains have been nucleated on ultrathin Co films by controlled surface touching using magnetic force microscopy tip in ultrahigh vacuum. The process of domain nucleation is due to strain induced perpendicular anisotropy on the surface of Co film. The smallest nucleated domain is 64 nm in diameter. The dependence of the size of the "written" domain on the time period of tip-sample contact has been measured.

Physical and magnetic microstructure of rapid thermally annealed thin film bismuth-doped garnets

Bismuth-doped iron garnets are promising materials for blue light magneto-optic recording media. These materials have been deposited on glass substrates with bulk magnetic and magneto-optic properties suitable for magneto-optic recording. However, these films exhibit a very low carrier to noise ratio (CNR) when crystallized in conventional furnaces. The low CNR is due to the inability to write circular domains in these materials. Rapid thermal annealing (RTA) has been reported to produce films with a much finer grain size. We have confirmed by transmission electron microscopy that RTA does indeed reduce the grain size over an order of magnitude from films crystallized in a conventional furnace. Faraday microscopy has shown that films processed by RTA with smaller grain size (∼30 nm) support circular magnetic domains of much greater regularity than films crystallized in conventional furnaces. The improved regularity of static thermomagnetically written domains, in films crystallized by RTA, lends promise that the noise in these materials can be reduced.

Improved longitudinal magnetic shielding by an amorphous FeSi steel composite panel

An improved magnetic shielding using the magnetic shaking technique with a planar mesh coil is applied to develop a composite shielding panel of Fe-based amorphous sheet and Si steel sheet. The mesh coil, sandwiched by the two ferromagnetic materials, makes a two-dimensional shaking field that enhances magnetic shielding. The composite panel annealed without field shows exceedingly high longitudinal shielding effectiveness. Fine and circular magnetic domains of amorphous Fe-based ribbons contribute to the magnetic shielding effectiveness for alternating fields at high frequencies.

電磁鋼・鉄基非晶質合金複合材料の磁気シールド特性

An improved magnetic shielding method using the magnetic shaking technique with a planar mesh coil was used to develop a composite shielding panel consisting of Fe-based amorphous sheets and Si-steel sheets. The mesh coil, sandwiched by the two ferromagnetic materials, creates a two-dimensional shaking field that enhances magnetic shielding. The composite panel, annealed without the application of a field, shows an exceedingly high shielding effectiveness of 470. The fine and circular magnetic domains of Fe-amorphous ribbons annealed without the application of a field contribute to the magnetic shielding effectiveness of alternating fields at high frequencies.

Measurement of magnetic bubble mobility in epitaxial garnet films

A technique for measuring the velocity of a circular magnetic domain in a magnetic field gradient is described. The method has been applied to epitaxial garnet films, and results are presented for a film of nominal composition Eu1Er2Ga0.7Fe4.3O12. The technique is compared with other methods of measuring domain wall mobility.

Theory of single-current domain propagation circuits

Single-current propagation circuits cause circular magnetic domains in a uniaxial ferrimagnetic wafer to move continuously by properly combining dynamic and static forces which vary periodically with distance. The dynamic force is due to a current and varies periodically with time at a frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</tex> . The static force has a spatial period one-half the period of the dynamic force. The static force may be produced by a periodic array of Permalloy elements or by a periodic modulation of wafer thickness. The general principle is discussed and a simple mathematical model is used to indicate the optimum amplitude and phase of the static force relative to the dynamic force. Single-current propagation circuits [1] cause circular magnetic domains in a uniaxial ferrimagnetic wafer to move continuously by properly combining dynamic and static forces which vary periodically with distance and have an average value of zero. The dynamic force is due to a current and varies periodically with time at a frequency <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</tex> . The second is static and has a spatial period one-half the period of the dynamic force. The static force may be produced by a periodic array of Permalloy elements [2], [3] or by a periodic modulation of wafer thickness [4]. The general principle is outlined in Figs. 1 and 2.

Magnetization of Small Permalloy Circuit Elements

Small thin-film elements of permalloy are being used in circuits for propagating circular magnetic domains in an adjacent uniaxial wafer. This paper shows that these elements often are not magnetically saturated and, therefore, exhibit pole distributions which depend on the applied field and geometry of the element. Approximate relations are derived from numerical solutions of a number of specific cases to aid the design and understanding of these circuits.

Logic functions for magnetic bubble devices

An analysis has been made of the number and types of logical functions which can be performed using the interaction of circular magnetic domains in rare earth iron oxides. Multiple logic functions are found to be produced simultaneously at any logical area. These conjunctive output sets have been categorized. Several conjunctive logic gates have been designed, fabricated, and tested successfully in Sm <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.55</inf> Tb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.45</inf> FeO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> using Permalloy overlays. Utilizing a circuit in which AND/OR logic gates are coupled to a dynamic memory bank, the total correlation of two data streams has been performed. It is shown how this multiply accessed dynamic memory serves to establish the correlation threshold.

Circular domain velocity versus force

A simple technique for measuring the velocity versus force curve of a circular magnetic domain has been devised. The technique consists of moving a domain under a straight current conductor which is adjacent to the surface of the wafer. A square-wave current is applied and the amplitude adjusted until the domain jiggles back and forth under the conductor a distance equal to R , where R is the radius of the domain. The blurred domain is observed using the Faraday effect. The magnitude of the effective driving field for a conductor with a width equal to R , spaced 0.1 h above the wafer, is 0.158 I/h when R = h ( h is the wafer thickness). The velocity is equal to 2 Rf .

Single-Conductor Magnetic-Bubble Propagation Circuits

Propagation circuits for circular magnetic domains using only a single electric current conductor are described. A circuit which in addition uses Permalloy dots for domain stability and for determining the direction of propagation has been operated at 475 kHz with a 100-mA amplitude current.

The Theory of Cylindrical Magnetic Domains

The theory of cylindrical magnetic domains provides conditions governing the size and stability of circular cylindrical magnetic domains in plates of uniaxial magnetic materials together with an estimate of the range of applicability of these conditions. The results of the theory are directly applicable to the design of cylindrical domain devices. Computation to first and second order of the energy variation resulting from general small deviation in the domain shape from an initially circular shape yields the conditions governing domain size and stability. The physical origin of the various terms in the energy expansion is examined in detail. A graph from which many domain size and stability properties may be obtained summarizes the results of the energy variation calculation. The minimum theoretically attainable domain diameter is approximately σ w /πM2 s , where σ w is the wall energy density and M s , is the saturation magnetization. For domains to exist, the effective anisotropy field must be greater than 4πM s .

Material requirements for circular magnetic domain devices

The material requirements of circular cylindrical domain devices are discussed. The current status of the search for circular domain materials is summarized with respect to the anisotropy field H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</inf> and the saturation magnetization M <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> by a chart showing the influence of these quantities on the size, stability and mobility of the circular domains. A preferred region is defined on the chart and representative materials are plotted. At the present time, the preferred region is most closely approached by certain mixed rare-earth orthoferrites and the aluminum substituted hexagonal ferrites.