G.A. Jones

Monocrystalline hexagonal-close-packed and polycrystalline face-centered-cubic Co nanowire arrays fabricated by pulse dc electrodeposition

Cobalt nanowire arrays have been grown onto anodic aluminum oxide templates by using a pulse dc electrodeposition technique. We demonstrate that the crystal structure, grain size, and related magnetic properties can be controlled by applying different pulse frequencies. For a pulse frequency of 25Hz, monocrystalline hexagonal-close-packed Co nanowires are formed with a well defined [101¯0] growth axis along the wire length. At a higher pulse frequency of 1000Hz, face-centered-cubic Co nanowires are deposited with a small grain size and a preferred [111] texture directed along the length of the wire. Possible mechanisms for the observed growth characterization are discussed. An investigation of the corresponding magnetic properties indicates that the fcc Co nanowire arrays have the larger coercivity and squareness values: reasons for this behavior are explored.

Co-rich cobalt platinum nanowire arrays: Effects of annealing

The effects of annealing on the crystal structure and magnetic properties of Co-rich cobalt platinum nanowire arrays embedded in anodic aluminium oxide membranes have been investigated. For this purpose, a rapid thermal annealing to temperatures of 300°Cto800°C has been used. Transmission electron microscopy and scanning electron microscopy show that the nanowires have a mean diameter of 14nm and an estimated wire density of 7.8×1010cm−2. From x-ray diffraction patterns, we find that the nanowires are hcp and possess a preferred texture in which the c axis of the grains tends to lie along the major axis of the wire. Vibrating sample magnetometry measurements indicate that the easy axis is along the nanowire axis direction. Hysteresis loops, saturation magnetization, squareness ratio (Mr∕Ms), and coercivity (perpendicular and parallel to the nanowire axis) have all been investigated as a function of the annealing temperature (TA). Coercivity parallel to the wire axis first increases with TA, attains a maxi...

The magnetic domain structure of partially crystallized amorphous Fe—B alloys by electron microscopy

Abstract A detailed electron microscopy study has been made of the crystallization behaviour up to 500°C of some amorphous FeB alloys together with accompanying changes in domain structure. Across the whole composition range investigated, crystallization involves the creation of small grains of bcc α-iron as well as larger spherulites comprised mostly of Fe3B. Both stages of the crystallization process produce remarkable changes in the domain structure, e.g. the formation of magnetization ripple, which to some extent are composition-dependent. These changes are discussed in some detail and models proposed to explain them.

The structure of electroless cobalt films as revealed by electron microscopy

A brief survey, using transmission electron microscopy, of the crystallite structure of magnetic electroless cobalt films deposited from an alkaline hypophosphite bath on to glass substrates has been undertaken. With increasing pH values from 7.4 to 8.5, the overall continuity of the films improved for a given thickness, although the crystallites themselves became individually isolated. This isolation is responsible for the increase in coercivity observed over the same pH range. Micrographs of various specimens are included to illustrate the features discussed.

Room-temperature electroless deposition of high-coercivity Co-Ni-P films

A plating solution has been developed for the electroless deposition of magnetic Co-Ni-P films on flexible substrates. The solution enables chemical deposition at room temperature (300 K). The coercivity of the deposited film is 120 kA m-1 for a film thickness of 100 nm.

Crystallization and Domain Properties of Thinned Amorphous FeBSi Ribbon.

A transmission electron microscope study has been made of the crystallization and associated domain behavior of an amorphous Fe82B15Si3 alloy. The first obvious signs of crystallization in microscope‐annealed foils occur at a temperature of about 345 °C with the appearance of α‐iron nuclei. These crystallites grow with annealing time but the grain size at complete crystallization is still small (∼0.1 μm). At a temperature of 500 °C a bct Fe2B phase is formed. Furnace annealed specimens differ in that the iron nuclei have a dendritic morphology. The as‐quenched material shows an isotropic domain structure with no magnetization ripple. The onset of crystallization is accompanied by the formation of this magnetization dispersion and, in some cases, stripe domains which reflect a perpendicular anisotropy. The results of in‐situ magnetization observations of the domain structure clearly indicate the perturbing effects of the crystallization products.

Generalized theory and application of Stokes parameter measurements made with a single photoelastic modulator

We report in this paper a generalized theory that describes the interaction between a monochromatic light beam and an optical system that includes one photoelastic modulator, one analyzer, and one photodetector. Based on the theory, a detailed four-step procedure is presented, which allows a precise measurement of the four Stokes parameters. An analysis of the systematic and random errors arising from the four-step measurements is also given as well as a calibration procedure that involves the use of a general retardation plate. As a practical application the procedure is used to analyze the magneto-optical properties of magnetic thin films grown on GaAs(001) substrates.

Composition-dependent structural and magnetic properties of Co1−xPtx (0.09⩽x⩽0.86) nanowire arrays

Highly ordered 14nm diam cobalt platinum alloy nanowire arrays with Pt content ranging from 9to86at.% have been electrodeposited into nanoporous anodic aluminum oxide templates. The crystal structure of the as-deposited Co1−xPtx nanowire arrays changes progressively from hcp to a mixture of hcp and fcc phases and finally to pure fcc with increasing Pt content. The coercivity, squareness, and saturation magnetization of the as-deposited nanowire arrays have been investigated as a function of nanowire composition.

The microstructure and magnetic properties of a permanent magnet alloy in the FeAlC system

Specimens of the alloy FeAl 7.74 C 1.77 have been quenched from 1200°C at different rates and annealed at 350°C for various times to optimise their magnetic properties. The remanent magnetisation and saturation magnetisation were found to increase at the expense of coercivity as the quench rate was reduced. A similar effect was observed during heat treatment at 350°C. X-ray diffractometry suggests that the transformation of austenite into ferrite and K-carbide is responsible for the increase in saturation magnetisation observed during heat treatment. Transmission electron microscopy revealed a finely divided micro-structure consisting of Widmanstatten type ferrite regions in a matrix of austenite and K-carbide. Preliminary studies of the domain structure indicate that domain wall impedance at the boundaries of the ferrite and K-carbide phases is a contributing factor to the coercivity of this material.

Domain structures in rapidly annealed Fe/sub 7/Co/sub 18/B/sub 14/Si/sub 1/

Amorphous ribbons of Metglas 2605CO (Fe/sub 67/Co/sub 18/B/sub 14/Si/sub 1/) have been rapidly annealed in a transverse (i.e. at right angles to the ribbon axis) magnetic field at temperatures close to the Curie point. Stress is not totally relieved but the domain structure largely consists of straight walls lying parallel to the applied field direction. More interesting is the presence of finely spaced walls running perpendicular to the direction of the magnetization vector in the main domains. These wall features indicate considerable dispersion of the magnetization, a conclusion borne out by their behaviour in externally applied fields both parallel and perpendicular to the ribbon axis. >