I.Z. Rahman

A review on magneto-impedance effect in amorphous magnetic materials

Abstract Recently the magneto-impedance (MI) effect in soft magnetic amorphous wires and ribbons has attracted wide interest both for its application as sensitive magnetic field and current sensors and for studying from a physical point of view. This phenomenon is mainly observed in a series of Co and Fe-based amorphous magnetic wires and ribbons and change in MI as high as 360% have been observed. After suitable heat treatment, sensitivity can be further improved. This behaviour is related to the magnetic domain structure and magnetisation dynamics of the materials. The MI effect has potential applications in super sensitive sensors, high speed computer peripherals, micromagnetics, information apparatus, mechatronics, automobile, industrial robots, power electronics, medical electronics and industrial process control. In this paper we have reviewed the current state of research on this phenomena, particularly, the alloy preparation, measurement system and various annealing techniques used in the MI effect enhancement.

The coercivity dependence of giant magneto-impedance effect in Fe–Cu–Nb–Si–B based metallic alloy ribbon at different crystalline stages

Abstract We have studied the giant magneto-impedance (GMI) effect in one Fe-based FINEMET alloy ribbon with nominal composition Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 (at %). DTA experiments were conducted to identify the primary and secondary crystallization temperatures. XRD, SEM and EDAX were performed to identify the phases at various crystalline stages. Static magnetic properties of the ribbons were measured using a VSM. Coercivity was found to be a strong function of annealing temperature, and this, in turn depended on the size and type of the crystalline phases. The maximum MI effect of 103.4% was observed at annealing temperature of 600°C. It was found that a small change in DC coercivity as a result of annealing greatly changed the MI ratios of the crystalline ribbons. Annealing above the secondary crystallization temperature caused the precipitation of Fe 2 B and Fe 3 B phases, which induced magnetic hardening and eliminates MI sensitivity.

Magnetic and Physical Characterization of Nano Granular Ni-Zn-Cu Based Ferrite Powders

Copper substituted Ni-Zn ferrite powders with nominal compositions of 4 2 x 2 . 0 ) x 8 . 0 ( O Fe Cu Zn Ni − (where, x = 0.0 to 0.6) were prepared by chemical co-precipitation, followed by calcining at different temperatures (20 0 C to 1000 C). Their physical and magnetic properties were studied using XRD, EDX, AFM and VSM techniques. These studies revealed the growth of crystal size and well-defined crystalline structure at higher calcination temperatures. The average particle size of samples changed from ~10 n m for as-dried to ~100 nm for samples calcined at 1000 C for this series of ferrites. The lattice paramete rs of the series of ferrite powders were found to vary almost linearly with addition of copp er. This is due to the substitution of divalent metal ion Cu by Ni in the octahedral sites. For small concentrations ) 3 . 0 to 05 . 0 ( ≤ ≥ of copper, linear decrease of magnetization was found but for higher concentrations ) 42 . 0 (≥ , deviations from this behaviour were observed.

Thickness and pore size dependence of coercivity for nanonetwork of iron produced by template synthesis

In this article we have studied thickness and pore size dependence of coercivity in iron films over the thickness range 1.875–45 nm at which Neel-type domain wall dominates. Nanonetwork of iron films were sputter deposited on commercial nanochannel alumina templates with nominal pore diameters of 20, 100, and 200 nm. Continuous films deposited on conventional glass substrates have also been studied in order to understand the effect of porosity on an otherwise nonporous film. While nanonetworks showed expected higher coercivity values than their continuous counterpart, it was found that the coercivity for nanonetworks was influenced by the thickness and the effective pore diameter of the deposited iron layer. Coercivity for conventional films on glass followed an inverse power law. For nanonetworks, thickness dependence of coercivity was complex and showed convolutions. An empirical thickness dependence of coercivity is proposed to explain the behavior of the thickness-varying coercivity for the nanonetworks.

Fabrication and measurements on polymer bonded NdFeB magnets

Abstract This paper presents measurements on polymer bonded NdFeB permanent magnets. These permanent magnets are fabricated by mixing NdFeB ribbons and binder epoxy resin under 5 ton/cm 2 pressure. The ribbons of NdFeB alloy are prepared by melt-spinning process. The performances of ribbon quenched at different rates and polymer bonded magnet are investigated by x-ray diffraction, DTA, SEM and VSM. The crystal lattice constants of the main phase Nd 2 Fe 14 B are found to be a = 8.73 A, c = 12.48 A. Effect of annealing at different temperature and time are also investigated.

Growth of Ni-Nanowires by Electrodeposition Technique

Nickel nanowires were grown by electrodeposition onto nanochannel Al 2O3 membranes (NCA: AnodiscTM 13), which have a nominal pore diameter of 200 nm. One side of the NCA wa s sputtered with aluminium to make ohmic contact and nickel was elect rod posited from the other side. Nickel ions in solution migrate into the pores by the action of electrical potential forming metallic wires embedded in an aluminium-oxide matrix. Density of nickel nanowires in the matrix was found to be approximately 80% of solid-metal density. The growth of ni ckel nanowires was investigated by Focused Ion Beam (FIB) and Scanning Electron Mic roscopy (SEM). The FIB images of the cross section showed that about 85% of the wires sta ted growing from the sputtered Aluminium substrate. Some of them started from middle of the pores. In order to understand this growth behaviour, NCA was examined. The heterogeneous growth of the ni ckel anowires can be attributed to the solution parameters as well as the branching of a lumin pores that prevail only on the filtration side. X-ray diffraction spectrum showed that nickel nanowires had a preferred orientation of (111), though the orientation (200) and (220) varied according to the electrolyte temperature. The average crystallite size varied as a funct ion of both pH and the temperature of the baths. Magnetic measurements were carried out using Vibrating s ample magnetometer (VSM) by applying a dc field of 5.48 kOe parallel and perpendicular to the w ir axis. Highest coercivity obtained for 200 nm pore diameter NCA was 195 Oe for field applied in parallel direction for samples that were deposited for 30 minutes. Introduction Recent progresses on magnetism and magnetic materials have made magn tic nanostructures a particularly interesting class of materials for both scienti fic and technological explorations. Due to their intricate nanostructures, extremely small length scal e, low dimensionality and interplay among constituents, they often exhibit new and enhanced properties over their bulk counterparts. Nanoporous membranes like Nano Channel Alumina (NCA) are particularly suitable for the preparation of very high aspect ratio structures, because the rati o of the length and diameter of the pores can be very large. The magnetic properties of the nickel na nowires have been investigated by several groups in the recent years with a view to use these arr ays of wires as sensors and as well as high density data storage devices [1]. All these properties are st rongly influenced by the dimension and crystal properties of the wires, which again depend on the physi cal structure of the templates and the growth mechanism of the wires. In the present study we hav e investigated the dependence of growth and crystal structure of nickel nanowires on electrodeposit ion process parameters (especially the pH and the temperature). In an earlier investi gation, we characterized the membrane NCA in order to understand the growth of wires through the pores [2]. The X-ray diffraction pattern revealed the preferential crystallographic orientation in nickel na nowires for different process parameters employed during the deposition and also the lattice para mete s of the unit cell of wires. Journal of Metastable and Nanocrystalline Materials Online: 2003-05-01 ISSN: 2297-6620, Vol. 17, pp 1-8 doi:10.4028/www.scientific.net/JMNM.17.1

Nanostructural characterisation of a thin film network of magnetic iron oxide

Nanostructured networks of maghemite formed by sputtering an iron target onto the surface of nanochannel alumina (NCA) templates have been studied using transmission electron microscopy, atomic force microscope, and Magnetic force microscopic. It has been found that the roughness of NCA originates from its fabrication history and largely affected by the size and distribution of nanopores. Magnetic properties of the iron oxide network are influenced by the surface morphology of the underlying template.

Development of metallic glass loaded polymer paste

Abstract The electronics industry has been working towards the development of microsystems that achieved through miniaturization of components. Inductive components have resisted this trend due to problems in reducing the size of the magnetic core. A reduction in the size of the core leads to an increase in the operating frequency of the device. At high frequencies the properties of traditional soft magnetic materials are greatly diminished. A new material needs to be developed, which can be compatible with existing electronic production technology, e.g., screen printable thick film pastes. The important properties required in these materials would be low coercivity, low core losses, and high initial permeability. Metallic glasses in the ribbon form have been used as cores in many applications such as, power transformers and power amplifiers. In ribbon form, metallic glasses are not suitable for many engineering applications that require the product to be more complex in configuration and geometry. To solve this problem, generally the material is converted to powdered form. In this paper we investigate the development of a metallic glass loaded polymer paste using metallic powder prepared from precursor amorphous ribbons. The ribbon, powder and paste samples were characterized using a number of techniques: DSC, vibrating sample magnetometer, X-ray diffraction and impedance analyzer.

Thermomagnetic recording properties of novel bismuth-substituted garnet films

Abstract The effects of various reflecting layers on the magneto-optical recoding properties of BiGaYIG films are reported. The thickness and composition of the reflecting layer are important for thermomagnetic recording quality. A static tester was build to write domains at various temperatures and fields. In the samples tested, the written domains were regular, reproducible and stable in the presence of magnetic stray fields. Films with thicker Al+Cr and Al-doped Cr reflectors were found to be easier to write domains.

Templating for the fabrication of nanostructured network of iron

In this work we present characterisation results of patterning of iron thin films with nanochannel alumina (NCA). Fe films were sputter deposited on the surface of the pore walls to form a contiguous nanostructured network and were characterised in terms of coercivity and surface roughness as functions of film thickness and pore diameters within the template. Films deposited on non-porous glass substrates were also studied for comparison with templated networks.