Giant magnetoimpedance in rapidly quenched materials

Thin magnetic wires can present excellent soft magnetic properties (with coercivities up to 4 A/m), Giant Magneto-impedance effect, GMI, or rectangular hysteresis loops combined with quite fast domain wall, DW, propagation. In this paper we overview the magnetic properties of thin magnetic wires and post-processing allowing optimization of their magnetic properties for magnetic sensor applications. We concluded that the GMI effect, magnetic softness or DW dynamics of microwires can be tailored by controlling the magnetoelastic anisotropy of as-prepared microwires or controlling their internal stresses and domain structure by appropriate thermal treatment.

Development of Magnetic Microwires for Magnetic Sensor Applications.

The influence of magnetic anisotropy, post-processing conditions, and defects on the domain wall (DW) dynamics of amorphous and nanocrystalline Fe-, Ni-, and Co-rich microwires with spontaneous and annealing-induced magnetic bistability has been thoroughly analyzed, with an emphasis placed on the influence of magnetoelastic, induced and magnetocrystalline anisotropies. Minimizing magnetoelastic anisotropy, either by the selection of a chemical composition with a low magnetostriction coefficient or by heat treatment, is an appropriate route for DW dynamics optimization in magnetic microwires. Stress-annealing allows further improvement of DW velocity and hence is a promising method for optimization of DW dynamics in magnetic microwires. The origin of current-driven DW propagation in annealing-induced magnetic bistability is attributed to magnetostatic interaction of outer domain shell with transverse magnetization orientation and inner axially magnetized core. The beneficial influence of the stress-annealing on DW dynamics has been explained considering that it allows increasing of the volume of outer domain shell with transverse magnetization orientation at the expense of decreasing the radius of inner axially magnetized core. Such transverse magnetic anisotropy can similarly affect the DW dynamics as the applied transverse magnetic field and hence is beneficial for DW dynamics optimization. Stress-annealing allows designing the magnetic anisotropy distribution more favorable for the DW dynamics improvement. Results on DW dynamics in various families of nanocrystalline microwires are provided. The role of saturation magnetization on DW mobility improvement is discussed. The DW shape, its correlation with the magnetic anisotropy constant and the microwire diameter, as well as manipulation of the DW shape by induced magnetic anisotropy are discussed. The engineering of DW propagation through local stress-annealing and DW collision is demonstrated.

Review of domain wall dynamics engineering in magnetic microwires

Magnetic microwires can present excellent soft magnetic properties and a giant magnetoimpedance effect. In this paper, we present our last results on the effect of postprocessing allowing optimization of the magnetoimpedance effect in Co-rich microwires suitable for magnetic microsensor applications. Giant magnetoimpedance effect improvement was achieved either by annealing or stress-annealing. Annealed Co-rich presents rectangular hysteresis loops. However, an improvement in magnetoimpedance ratio is observed at fairly high annealing temperatures over a wide frequency range. Application of stress during annealing at moderate values of annealing temperatures and stress allows for a remarkable decrease in coercivity and increase in squareness ratio and further giant magnetoimpedance effect improvement. Stress-annealing, carried out at sufficiently high temperatures and/or stress allowed induction of transverse magnetic anisotropy, as well as magnetoimpedance effect improvement. Enhanced magnetoimpedance ratio values for annealed and stress-annealed samples and frequency dependence of the magnetoimpedance are discussed in terms of the radial distribution of the magnetic anisotropy. Accordingly, we demonstrated that the giant magnetoimpedance effect of Co-rich microwires can be tailored by controlling the magnetic anisotropy of Co-rich microwires, using appropriate thermal treatment.

https://www.mdpi.com/1424-8220/20/6/1558/pdf

Optimization of magnetic properties and GMI effect of Thin Co-rich Microwires for GMI Microsensors.

Cylindrical micro and nanowires: Fabrication, properties and applications

The GigaHertz spin rotation (GSR) effect was observed through the excitement of Giga Hertz (GHz) pulse current flowing through amorphous wire. The GSR sensor that was developed provides excellent features that enhanced magnetic sensitivity and sine functional relationship, as well as good linearity, absence of hysteresis, and low noise. Considering the GHz frequency range used for the GSR sensor, we assume that the physical phenomena associated with the operation of the sensor are based on spin reduction and rotation of the magnetization. The proper production technology needed was developed and a micro-sized GSR sensor was produced by directly forming micro coils on the surface of the application-specific integrated circuit (ASIC). Some prototypes of the ASIC type GSR sensor have been produced in consideration of applications such as automotive use, mobile device use, and medical use. Therefore, we can conclude that GSR sensors have great potential to become promising magnetic sensors for many applications.

https://www.mdpi.com/1424-8220/20/4/1023/pdf

The Development of ASIC Type GSR Sensor Driven by GHz Pulse Current.

The development of a micro-coil-on-ASIC type GSR sensor driven by GHz pulse current

Micro-sized magnetic sensors with ultrahigh sensitivity are required in biomagnetic measuring devices. The gigahertz (GHz) spin rotation sensor, which is a coil-type magnetic sensor, shows high sensitivity while transmitting GHz-pulse currents. Detection magnetic fields are sensed via a pickup coil, which is wrapped around the wire when the GHz-pulse currents are applied. However, the micromechanism in the amorphous wire, which exhibits high sensitivity, has not yet been elucidated. In this study, we investigated how the fall time of the pulse current, which defines the frequency, affects the output peak voltages and the behavior of the magnetization inside the amorphous wire. We found that the shorter the fall time, the higher are the absolute values of the output peak voltage and the external magnetic field detecting those values. At a fall time of 0.385 ns, only the rotations of magnetization in the outer circumference of the amorphous wire contributed to the output voltages, and at a fall time of 5.0 ns, the domain wall motions inside the wire also contributed to the output voltages. This difference was the reason why the output peak voltages increased as the fall time was shortened.

Effects of Fall Times of Pulse Currents on Output Voltages in Amorphous-Wire-Based Magnetic Sensors

[과제] GSR 센서 소자에 있어서, 상승 펄스 검파의 tm과 ti가 가까워 시간 tm에서는 유도 전압은 상당한 크기를 가지고 있어, 그 자계에 의한 변동은 무시할 수 없다. 출력 전압으로부터 유기 전압을 제거하여, 상승 펄스 검파 방식의 GSR 센서를 실현한다. [해결 수단] 유도 전압이 자성 와이어에 흐르는 전류의 방향에 대해서 양음이 반대로 된다는 지견에 기초하여, 하나의 코일 내에 양음이 반대 방향인 전류가 흐르는 2개의 자성 와이어를 설치함으로써 유도 전류가 상쇄되어 자계에 비례하는 전압을 검출할 수 있다.

Gsr 센서 소자

In a GSR sensor element, tm and ti of rising pulse detection are close, and the induced voltage is significantly high at tm. Thus, a variation due to the magnetic field cannot be ignored. To remove an induced voltage from an output voltage and achieve a GSR sensor with a rising pulse detection system. On the basis of the knowledge that the polarity of an induced voltage becomes opposite relative to a direction of the current flowing in a magnetic wire, if one coil includes therein two magnetic wires in which currents of opposite polarities flow, an induced current is cancelled, allowing for the detection of a voltage in proportion to a magnetic field.

Shinpei Honkura

Papers

The Development of ASIC Type GSR Sensor Driven by GHz Pulse Current.

The development of a micro-coil-on-ASIC type GSR sensor driven by GHz pulse current

Effects of Fall Times of Pulse Currents on Output Voltages in Amorphous-Wire-Based Magnetic Sensors

Gsr 센서 소자

Gsr sensor element