A 50 nm-thick Co film has been grown either on the free surface (surface roughness, $6 nm) or on the wheel-side surface (surface roughness, $147 nm) of Co 84.55 Fe 4.45 Zr 7 B 4 amorphous ribbons. A comparative study of the giant magnetoimpedance (GMI) effect and its field sensitivity (g) in the uncoated and Co-coated ribbons is presented. We show that the presence of the Co coating layer enhances both the GMI ratio and g in the Co-coated ribbons. Larger values for GMI ratio and g are achieved in the sample with Co coated on the free ribbon surface. The enhancement of the GMI effect in the Co-coated ribbons originates mainly from the reduction in stray fields due to surface irregularities and the enhanced magnetic flux paths closure. These findings provide good guidance for tailoring GMI in surface-modified soft ferromagnetic ribbons for use in highly sensitive magnetic sensors. The discovery of the so-called giant magnetoimpedance (GMI) effect in soft ferromagnetic ribbons makes them attractive for magnetic sensor applications. 1,2 GMI is a large change in the ac impedance of a ferromagnetic conductor subject to a dc magnetic field. 1 The impedance (Z) of a ferromagnetic ribbon can be calculated by 3 Z ¼ R dc jka cothðjkaÞ;( 1) where a is half of the thickness of the ribbon, R dc is the electrical resistance for a dc current, j ¼ imaginary unit, andThe impedance is related to the skin effect characterized by the skin depth (d m ), which, in a magnetic medium, is given bywhere q is the electrical resistivity, m T is the transverse magnetic permeability, and f is the frequency of the ac current. The application of a dc magnetic field H dc changes m T , and consequently d m and Z. Since GMI is observed at high frequencies (>1 MHz), the skin effect is significant enough to confine the ac current to a sheath close to the surface of the conductor; GMI is therefore a surface-related magnetic phenomenon. 2,3 As such, the surface roughness of a material is important and can considerably reduce the GMI magnitude if the surface irregularities exceed the skin depth. [4][5][6][7] As an example, reducing the surface irregularities of Co-based amorphous ribbons by chemical polishing was found to greatly enhance the GMI effect. 8 Peksoz et al. recently reported that the coating of the Co-based ribbon surface with CuO or a diamagnetic organic thin film improved the GMI effect. 9,10 While the origin of the enhanced GMI effect in the samples 9,10 is not well understood, these investigations open up new opportunities for improving GMI effect in soft ferromagnetic ribbons. We report here a comparative study of the GMI effect and its field sensitivity (g) in Co 84.55 Fe 4.45 Zr 7 B 4 amorphous ribbons with and without 50 nm thick Co layers deposited on either the free ribbon surface (surface roughness, $6 nm) or on the wheel-side ribbon surface (surface roughness, $147 nm). This composition has a high Curie temperature compared to Fe-based amorphous alloys 11 and is responsive to field annealing. 12 We find a large enhancement of th...

To study the effect of non-magnetic layer (Cu) on magnetic properties of antiferromagnetic FeMn, multilayers of Ta(5 nm)/[FeMn(t)/Cu(5 nm)]10/Ta(5 nm), where t is varied in the range of 5–15 nm, are fabricated by a combination of RF and DC magnetron sputter deposition. Magnetization curves for these samples exhibit magnetic hysteresis, and when the samples are cooled in an applied magnetic field, the hysteresis loops are shifted. This shift is attributed to an “intrinsic” exchange bias effect (i.e., it is observed without a separate ferromagnetic layer). Presented temperature and thickness dependences of the coercive field, magnetic moment, and exchange bias field provide insights into the origin and mechanism of the observed intrinsic exchange bias.

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Magnetic force microscopy was performed on 300 nm thick magnetite films grown epitaxially on MgO (001) at temperatures ranging from well below to well above the Verwey transition temperature, TV. Frequency shift images were acquired at different locations on the sample as temperature was increased through the Verwey transition. The magnetic domain features are persistent at all temperatures, which indicates that the domains are pinned across the phase transition, probably due to antiphase boundaries. An enhancement of magnetic contrast below TV indicates the moments tilt out of the plane below TV, which is corroborated by superconducting quantum interference device magnetometry.

3000 Å Fe3O4 (magnetite) thin films were simultaneously grown on (001) MgO single crystal substrates with and without 30 Å buffer layers of Fe, Cr, Mo, and Nb. For all samples, the Verwey transition temperature (TV) occurs between 119 and 125 K, indicating good oxygen stoichiometry. We observe highly oriented (001) Fe3O4 with Mo and no buffer layer, reduced (001) texture with Nb and Fe, and polycrystalline growth with Cr. Mo, Cr, and unbuffered magnetite show typical magnetic behavior, whereas Nb and Fe buffers lead to anomalous magnetic properties that may be due to interfacial reactivity.