Ultra-soft magnetic Co-Fe-B-Si-Nb amorphous alloys for high frequency power applications

Abstract

With the continuous shrinkage of the footprint of inductors and transformers in modern power supplies, higher flux, while still low-loss metallic replacements of traditional ferrite materials are becoming an intriguing alternative. One candidate replacement strategy is based on amorphous CoFeBSi soft-magnetic alloys, in their metallic glass form. Here the structural and magnetic properties of two different families of CoFeBSi-based soft magnetic alloys, prepared by arc-melting and subsequent melt spinning (rapid quenching) are presented, targeting potential applications at effective frequencies of 100 kHz and beyond. The nominal alloy compositions are Co67Fe4B11Si16Mo2 representing commercial Vitrovac and Co72-xFexB28-y (where B includes non-magnetic elements such as Boron, Silicon etc. x varies between 4 and 5 % and y is varied from 0 to 2 %) denoted Alloy #1 and prepared as a possible higher performance alternative, i.e. lower power loss and lower coercivity, to commercial Vitrovac. Room temperature magnetization measurements of the arc-melted alloys reveal that compared to Vitrovac, Alloy #1 already presents a ten-fold decrease in coercivity, with Hc ∼ 1.4 Am-1 and highest figure of merit of (Ms/Hc > 96). Upon melt-spinning the alloys into thin (< 30 μm) ribbons, the alloys are essentially amorphous when analyzed by XRD. Magnetization measurements of the melt-spun ribbons demonstrate that Alloy #1 possesses a coercivity of just 2 Am-1, which represents a significant improvement compared to melt-spun ribbons of Vitrovac (17 Am-1). A set of prototype transformers of approximately 10 turns of Alloy #1 ribbon exhibits systematically Hc < 10 Am-1 at 100 kHz, without a noticeable decrease in coupled flux and saturation.

Structures and Functional Properties of Amorphous Alloys

“…Compared with conventional magnetic materials, amorphous alloys exhibit nice magnetic softness and good ductility. [ 86,87 ] Amorphous alloys usually exhibit a low saturated magnetization ( B s ) due to the decrease of the 3d outer‐shell electrons of ferromagnetic elements. [ 88 ]…”

Investigation of Mechanical and Magnetic Properties of Co-Based Amorphous Powders Obtained by Atomization

“…CoFeSiB soft magnetic alloys are excellent candidates for such applications due to high electrical resistivity. The most popular soft magnetic Co-based alloy is a material called Vitrovac and its modifications [ 28 , 29 ] which are characterized by relatively low coercivity, high saturation magnetization, low eddy current and high magnetic permeability.…”

Giant Stress Impedance Magnetoelastic Sensors Employing Soft Magnetic Amorphous Ribbons

“…In addition to that, these alloys show optimal chemical, mechanical, and magnetoelastic properties. including resistance to corrosion, high tensile stress and Young modulus, uniformity, thin shapes, low size (enabling miniaturization and high-frequency devices), and high magnetic permeability [4,5]. The combination of all these properties turns these alloys into suitable materials for the design of different kinds of sensors with high sensitivity, low cost, and quick response [6].…”