D. García

Magnetic behavior of an array of cobalt nanowires

Cobalt nanowires have been electrodeposited into the pores of Anodisc™ alumina membranes after placing on one side a layer of sputtered copper, which acts as electrode and substrate during the electrodeposition. Nanowires are 60 μm long, 170–220 nm in diameter depending on the size of the pores of the alumina membrane. This array of nanowires exhibits uniaxial magnetic anisotropy related to the particular shape of each individual nanowire. On the contrary to the expected behavior in a uniaxial magnetic system, the coercivity of the array exhibits a maximum when the applied field is in a perpendicular direction with respect to the easy axis. This magnetic behavior is analyzed considering dipolar interactions among nanowires, and the magnetization of the array is obtained as a function of the magnetic characteristics of each nanowire using an iterative method.

Frequency dependence of giant magnetoimpedance effect in CuBe/CoFeNi plated wire with different types of magnetic anisotropy

A giant magnetoimpedance effect (GMI) has been measured in a CuBe 0.1 mm diameter wire, electroplated with a Co6Fe20Ni74 layer 1 μm thick. Heat treatments after the electrodeposition were performed under the dc or ac field. The GMI has been measured in the frequency range 0.25 to 9 MHz, using ac driving current from 5 to 35 mA. The maximum GMI ratio depends strongly on the heat treatments, the intensity and the frequency of the driving current, reaching the value of 165% for optimal conditions. Results are discussed, taking into account the anisotropy distribution in the magnetic layer induced by the heat treatments under the field and a simple rotation model.

Magnetoimpedance effect in CoFeNi plated wire with ac field annealing destabilized domain structure

Giant magnetoimpedance (GMI) behavior at 0.25 MHz has been studied for a composite wire consisting of a 1 μm thick Co6Fe20Ni74 magnetic layer electroplated onto a 0.1 mm diam CuBe nonmagnetic wire. This has been done for as-deposited samples as well as after annealing under dc and ac axial magnetic fields. In the optimum conditions, a maximum GMI of 150% is achieved. The observed GMI hysteresis in the as-prepared state decreases for high driving current used to measure the MI itself. Such hysteresis, to be avoided in technological applications, is also very much reduced after ac field annealing. GMI characteristics are analyzed considering the domain-wall stabilization occurring after the annealing treatments.

Influence of geometrical parameters on the giant magnetoimpedance response in amorphous ribbons

Abstract The magnetoimpedance (MI) has been studied in Fe 3 Co 67 Cr 3 Si 15 B 12 amorphous ribbons of variable length, with transverse induced magnetic anisotropy. The angular dependence of the MI has been examined for the angles 0⩽α⩽90°, where α is the angle between the long side of the ribbon and the external magnetic field. Angular dependencies of the magnetoimpedance ratio and field of the MI maximum show stable behaviour for angles up to 30°.

Influence of field annealing on the hysteretic behaviour of the giant magneto-impedance effect of Cu wires covered with Ni80Fe20 outer shells

Abstract The giant magneto-impedance (GMI) effect of Cu wires covered with a Ni–Fe/Ni–Co layered structure has been investigated in as-prepared and heat-treated states. A hysteretic behaviour of the GMI effect as a function of the applied field was observed. This hysteresis is related to the anisotropy field of the wires and can be reduced by field annealing.

The influence of the Pt buffer layer on the perpendicular magnetic anisotropy in epitaxial FePd(001) ordered alloys grown by sputtering

Single-crystalline FePd(001) 1000-A-thick films were grown at 500 °C by codeposition in an UHV sputtering system. It is found that both the crystalline structure and therefore the magnetic properties strongly depend on the Pt buffer layer thickness. The films grown on Pt(100) layers 50 A thick and thinner do not exhibit clear chemical order and show in-plane magnetic anisotropy. FePd grown on thicker Pt buffers adopts a fct structure accompanied by a strong chemical ordering, leading to a perpendicular magnetic anisotropy.

MFM imaging of FePd stripe domains. Evolution with Pt buffer layer thickness

Epitaxial FePd (0 0 1) thin films grown by UHV sputtering onto different Pt buffer layers have been studied by magnetic force microscopy. Samples with buffer thickness down to 150 A present high perpendicular magnetic anisotropy. Both the stripe domain width and the magnetic contrast increase with the buffer thickness, in agreement with the anisotropy deduced from the hysteresis loops.

Development of a tensile-stress-induced anisotropy in amorphous magnetic thin films

Abstract Magnetic anisotropy was induced in positive magnetostrictive Fe 80 B 20 and negative magnetostrictive Co 75 Si 15 B 10 thin films by developing a tensile stress within the samples. The films were grown on the concave surfaces of mechanically bowed glass substrates. On releasing the substrates from the substrate holders, a tensile stress was developed within the samples that modified the domain structure. As a result of it, a magnetic easy axis parallel to the direction of the stress was induced in FeB sample whereas in CoSiB sample the induced easy axis was perpendicular to the direction of the developed stress. To produce magnetic multilayers with crossed anisotropy, FeB/CoSiB bilayers and FeB/Cu/CoSiB trilayers were grown on bowed substrates. The study of magnetic properties of the multilayers indicates the development of crossed anisotropy within them, particularly when the magnetic layers are separated by a nonmagnetic Cu layer.

Anisotropy induced by the bowed-substrate sputtering technique in positive/negative magnetostriction FeB/CoSiB bilayers

CoSiB and FeB single layers and CoSiB/FeB bilayers with thicknesses ranging from 250 to 1500 A were grown on bowed glass substrates using rf sputtering. A magnetoelastic anisotropy was induced in the magnetic layers after removing the films from the sputtering chamber. The positive (FeB) and the negative (CoSiB) magnetostrictive single layers showed an easy magnetization axis transverse and parallel to the compression axis, respectively. The magnetic behavior of the CoSiB/FeB bilayers is shown to be extremely sensitive to the thickness of each layer, to their thickness ratios, and also to the deposition sequence of the layers on the substrate. These results are discussed in terms of the interactions between two magnetic phases with easy magnetization axes transverse to each other.

Structure and magnetic anisotropies in sputtered FePd(1 1 0) thin films

The growth temperature dependence of structure and magnetic anisotropies is studied for epitaxial FePd(1 1 0) alloys grown by sputtering. Partial chemical order is obtained for growth temperatures of 600°C and above. Strong in-plane uniaxial magnetic anisotropy is found for chemically disordered samples grown at 500°C, with a reduction in the anisotropy constants for samples grown at higher temperatures. The obtained anisotropy values can be interpreted as the result of the competition between magnetocrystalline and magnetoelastic anisotropy.