In a set of papers, the authors present a comprehensive investigation of the magnetic, structural, and dynamic properties of thin film Ni-Co, Ni-Fe, and Co-Fe alloys and uncover new phenomena in systems previously thought to be well understood and commonplace. High-precision measurements of saturation magnetization, effective magnetization, spectroscopic $g$ factor, inhomogeneous linewidth broadening, and damping are performed, allowing precise testing of \textit{ab initio} calculations for the orbital magnetic moment and the intrinsic magnetic damping, which is the most integral motivation of this work. Quantitative comparison between experiment and theory is shown and discussed for magnetic damping spanning a broad range of material parameters. Furthermore, a large set of data has been created that will serve as a glossary for alloy magnetic properties in thin films.

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Magnetic properties of ultrathin 3 d transition-metal binary alloys. I. Spin and orbital moments, anisotropy, and confirmation of Slater-Pauling behavior

The outstanding properties of selected soft magnetic materials make them successful candidates for building high performance sensors. In this paper we present our recent work regarding different sensing technologies based on the coupling of the magnetic properties of soft magnetic materials with their electric or elastic properties. In first place we report the influence on the magneto-impedance response of the thickness of Permalloy films in multilayer-sandwiched structures. An impedance change of 270% was found in the best conditions upon the application of magnetic field, with a low field sensitivity of 140%/Oe. Second, the magneto-elastic resonance of amorphous ribbons is used to demonstrate the possibility of sensitively measuring the viscosity of fluids, aimed to develop an on-line and real-time sensor capable of assessing the state of degradation of lubricant oils in machinery. A novel analysis method is shown to sensitively reveal the changes of the damping parameter of the magnetoelastic oscillations at the resonance as a function of the oil viscosity. Finally, the properties and performance of magneto-electric laminated composites of amorphous magnetic ribbons and piezoelectric polymer films are investigated, demonstrating magnetic field detection capabilities below 2.7 nT.

https://www.mdpi.com/1424-8220/14/5/7602/pdf

Sensor Applications of Soft Magnetic Materials Based on Magneto-Impedance, Magneto-Elastic Resonance and Magneto-Electricity

Thin-film magneto-impedance structures with very large sensitivity

The sensitivity of magnetic sensors based on the Giant Magneto-Impedance effect can be enhanced using high permeability materials with a well-defined but small transverse anisotropy. We describe an experimental study performed on multilayered, permalloy-based thin films deposited by sputtering under a magnetic field that produces a homogeneous uniaxial anisotropy in the plane of the film. Patterning of the deposit by photolithographic methods into strip-shaped samples (with their long direction perpendicular to the induced anisotropy) establishes a longitudinal shape anisotropy that competes with the transversal one induced at deposition. The combination and competition of the two mutually perpendicular uniaxial anisotropies result in an effective one with a reduced magnitude (the difference between both of them) in the transversal direction. As the strength of the shape anisotropy is determined by the relation between width and length of the stripe, the magnitude of the effective anisotropy can be conveniently modulated by adequately selecting the aspect ratio of the patterned sample. The hysteresis loops measured by Kerr effect magnetometry confirm that the effective transversal anisotropy field can be reduced from 5 to 1 Oe which should concomitantly increase the sensitivity of thin film magneto-impedance sensors.

Tailoring the magnetic anisotropy of thin film permalloy microstrips by combined shape and induced anisotropies

https://robots.iopscience.iop.org/article/10.1088/2631-8695/ac0838/pdf

Magnetic sensors-A review and recent technologies

Development of accurate measuring techniques is an important task for the high-frequency materials characterization. The magnetoimpedance (MI) of [Py(170 nm)/Ti(6 nm)]3/Cu(250 nm)/[Ti(6 nm)/Py(170 nm)]3 multilayer sandwiched structures is measured using two different high-frequency test fixtures and the results are compared for both cases. Sets of rectangular samples with different lengths and widths are fabricated by photolithography and inserted in test fixtures based either on microstrip or coplanar waveguides (CPWs). Measurements with CPWs ensure higher MI values, since their contribution to the total impedance is lower. Besides, we describe the de-embedding procedure that allows the subtraction of the external impedance brought about by the CPW from the total impedance that is measured using the test fixture. The intrinsic MI ratio of the thin-film structures, obtained by this de-embedding procedure, reaches 550%.

High-Frequency Magnetoimpedance Response of Thin-Film Microstructures Using Coplanar Waveguides

We compare two photolithographic methods to pattern magneto-impedance elements with micrometric dimensions, suitable to build magnetic microsensors. The magnetic material to be patterned is deposited by sputtering onto silicon wafers. It has a sandwiched structure where the outer magnetic layers are composed by a stack of permalloy and thin titanium layers and the central non-magnetic layer is made of copper. The total thickness is 1.31 μm. After preparation it displays an excellent magneto-impedance performance that is intended to be retained after the patterning procedure. For the lift-off method, a negative-type resist is deposited and patterned onto the silicon wafer prior to the material deposition. The undesired parts of the material are peeled off when removing the resist. Even for such a thick film, the quality of the obtained samples is quite good and the magneto-impedance response of the micro-shaped samples is great. In the wet-etching method, a positive-type resist is deposited and patterned onto the sputtered material. The parts that are not protected by the resist are etched using an acid solution. The different chemical behavior of the metals that constitute the sample severely challenges the wet-etching process. The results are poor, and the results compare unfavorably to those obtained by the lift-off process.

Ane Barrainkua

Papers

Tailoring the magnetic anisotropy of thin film permalloy microstrips by combined shape and induced anisotropies

High-Frequency Magnetoimpedance Response of Thin-Film Microstructures Using Coplanar Waveguides

Comparison of Micro-Fabrication Routes for Magneto-Impedance Elements: Lift-Off and Wet-Etching