Composition dependence of field induced anisotropy in ferromagnetic (Co,Fe)89Zr7B4 and (Co,Fe)88Zr7B4Cu1 amorphous and nanocrystalline ribbons

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...

mentioning

confidence: 75%

Enhanced giant magnetoimpedance effect and field sensitivity in Co-coated soft ferromagnetic amorphous ribbons

Laurita

Chaturvedi

Bauer

et al. 2011

“…A new class of Fe-Co-based amorphous and nanocomposite materials, HiTperms, [6][7][8][9][10][11][12] show promise for high frequency applications. Low losses, tunable anisotropies, and robust mechanical properties suggest their use in high efficiency, high speed motors both at room temperature and operating temperatures >300 C. For motors where material strength is critical, Co-rich compositions offer good soft magnetic properties without the brittleness found in Fe-rich alloys.…”

Section: Introductionmentioning

confidence: 99%

High speed electric motors based on high performance novel soft magnets

Silveyra

Leary

DeGeorge

et al. 2014

Self Cite

Novel Co-based soft magnetic materials are presented as a potential substitute for electrical steels in high speed motors for current industry applications. The low losses, high permeabilities, and good mechanical strength of these materials enable application in high rotational speed induction machines. Here, we present a finite element analysis of Parallel Path Magnetic Technology rotating motors constructed with both silicon steel and Co-based nanocomposite. The later achieved a 70% size reduction and an 83% reduction on NdFeB magnet volume with respect to a similar Si-steel design.

“…Recent suppression of the nucleation of the c-phase has been observed in Co-Fe-based nanocomposites at compositions where the binary Fe-Co phase diagram predict that the a-andcphases coexist. [3][4][5][6][7][8] In Fe-Ni-based nanocomposites, similar observations in Fe-rich alloys 11 show nucleation of the c-phase is suppressed in favor of a metastable a-phase.…”

Section: Introductionmentioning

confidence: 59%

“…2 Fe-based alloys have attracted the most attention, as optimized alloys exhibit relatively high magnetic flux densities and low losses. Co-based alloys, with small or zero magnetostriction, a relatively large response to magnetic field annealing [3][4][5][6][7][8] and excellent mechanical properties making them interesting for magnetic sensors and high frequency applications. 9,10 In transforming amorphous precursors to nanocomposite magnets, it is possible to suppress stable phase formation and exploit properties of metastable phases.…”

Section: Introductionmentioning

confidence: 99%

In-situ investigation of phase formation in nanocrystalline (Co97.5Fe2.5)89Zr7B4 alloy by high temperature x-ray diffraction

Kernion

Ohodnicki

McHenry

2012

Crystallization and phase evolution in an (Co 97.5 Fe 2.5 ) 89 Zr 7 B 4 amorphous alloy was studied by high temperature x-ray diffraction (HTXRD) and transmission electron microscopy (TEM). Co-based nanocomposite alloys have zero magnetostriction and a strong response to magnetic field annealing making them interesting for sensor and high frequency power applications. Amorphous alloys, synthesized by single roll melt-spinning, develop a nanocomposite structure after primary crystallization. After annealing at 540 C for 1 h, TEM images and diffraction patterns confirm a grain size of 19 nm and the presence of at least two phases. HTXRD results show preferential body centered cubic (bcc) nucleation and formation of multiple phases at various stages of crystallization. Only the face centered cubic (fcc) phase remained at temperatures above 600 C. On heating, the lattice parameter of the fcc phase increases at a rate higher than expected from thermal expansion. This is partially explained by an increase in the Fe-concentration in fcc crystallites.