J. Yamasaki

Measurement of saturation magnetostriction of a thin amorphous ribbon by means of small-angle magnetization rotation

A new method was developed to measure the saturation magnetostriction of a thin amorphous ribbon. It is based on the use of small-angle magnetization rotation to measure the change in anisotropy field caused by the tensile stress. Measurements have been performed on Metglas 2826, 2605, and Co-Si-B amorphous ribbons. The maximum experimental error of the measurement was estimated to be about ±5 percent. It is shown that the sensitivity of the method depends on the shape anisotropy field. The estimated sensitivity was about 2 × 10-7for Metglas 2826 ribbon with 1.8 mm × 40 μm × 12 cm in dimensions.

Anisotropic Nd–Fe–B thin‐film magnets for milli‐size motor

Efforts were made to obtain anisotropic thin‐film magnets at low substrate temperature. This is an important criterion for practical applications such as to build motors. The influence of substrate materials as well as film thickness on the c‐axis orientation were studied. It has been shown that thin‐film magnets with the easy axis of magnetization normal to the film plane could be deposited at a substrate temperature of around 450 °C by choosing the composition near the line from Nd13Fe76B11 to Nd13Fe70B17 in the ternary phase diagram. It was found that the anisotropic film magnets could be also deposited on the metallic substrate. The c‐axis orientation tended to be isotropic with an increase in film thickness. The obtained results were used to fabricate a milli‐size motor by depositing 20‐μm‐thick Nd–Fe–B films on a silicon steel disk substrate of 5‐mm diam. The milli‐size motor exhibited a torque of 0.8 g mm at a rotational speed of 3000 rpm.

Large Barkhausen effect and Matteucci effect in amorphous magnetostrictive wires for pulse generator elements

The mechanisms producing the sensitive large Barkhausen effect and the Matteucci effect in as-prepared amorphous magnetostrictive wires are investigated using colloid technique domain observations and Sixtus-Tonks domain propagation characteristics. Theoretical analysis of the pulse height of induced voltage at the pick-up windings and between both ends of the wire are made. This analysis is compared with experimental results. The Matteucci effect was remarkably improved by twisting or twisting then annealing the as-prepared wires. Jitter-less pulse generation is realized in the latter case.

Domain observations of Fe and Co based amorphous wires

Domain observations were made on Fe- and Co-based amorphous magnetic wires that exhibit a large Barkhausen discontinuity during flux reversal. Domain patterns observed on the wire surface were compared with those found on a polished section through the center of the wire. It was found that the Fe-based wire consists of a shell and core region with a third region between them. This fairly thick transition region made up of domains at an angle of about 45 degrees to the wire axis lacks the closure domains of the previous model. The Co-based wire does not have a clear core and shell domain structure. The center of the wire has a classic domain structure expected of uniaxial anisotropy with the easy axis normal to the wire axis. When a model for the residual stress quenched-in during cooling of large Fe bars is applied to the wire, the expected anisotropy is consistent with the domain patterns in the Fe-based wire. >

Jitter-less pulse generator elements using amorphous bistable wires

New jitter-less pulse generator elements are presented using amorphous magnetostrictive wires. These elements induce sharp voltage pulses with ∼ 6V/cm2.Oe.turn due to the large Barkhausen jumps and with ∼ 6V/cm3.Oe due to the Matteucci effect using external ac fields of more than 0.1 Oe at frequencies between 0.01 Hz - 10 k Hz. Jitter of the pulse inducing phase is less than 1/10 and the pulse height is about twice that of Wiegand wires, respectively. The critical field of the large Barkhausen jump is controlled by heat treatment, etching, or twisting the wires. These wires are expected to be useful for high-performance pulse generator elements for high resolution rotary encorders by combining them with magnet ring, torque sensors, proximity sensors and magnetometers.

Anisotropy pinning of domain walls in a soft amorphous magnetic material

Ribbons were annealed in the demagnetized state with one wall along the ribbon middle. This wall becomes pinned during the heat treatment. Reentrant reversal occurs when reverse domains are nucleated at the ribbon edge with a threshold field larger than the demagnetizing field; this wall does not annihilate when it meets the pinned wall but leaves a line of reverse domains stabilized by ripple in the anisotropy. These domains permit a regular smooth reversal for the demagnetization process until the ribbon returns to the pinned configuration. The regular loop appears when the ribbon has been completely saturated by a large field. Mobile walls are nucleated on both sides of the pinned wall so that the ribbon does not return to the pinned configuration. Reversal now follows the usual demagnetization curve over the entire cycle. Kerr magnetooptical domain and domain wall observations are used in this investigation. All of the possible wall structures predicted by the model of asymmetric flux closed Bloch walls were identified. >

Large Barkhausen discontinuities in Co‐based amorphous wires with negative magnetostriction

Magnetic properties, such as domain patterns and anisotropy, were measured for negative magnetostrictive Co‐Si‐B amorphous wires exhibiting large Barkhausen discontinuities and the results are compared to those of Fe‐Si‐B wires with positive magnetostriction. The Co‐based wire was found to have a bamboolike domain structure at the wire surface. It was also shown that the amorphous wires prepared by the in‐water quenching technique store tensile stress in the radial direction. The magnetostrictive anisotropy due to residual stress will produce an axial component of magnetization in conjunction with the two‐dimensional geometry of wires making both Co‐ and Fe‐based wires exhibit large Barkhausen discontinuities along the axis of the wire.

Bistable magnetization reversal in 50 µm diameter annealed cold-drawn amorphous wires

Amorphous magnetostrictive 50 μm diameter Fe 77.5 Si 7.5 B 15 wires exhibiting square and bistable hysteresis loops have been obtained by field-tension annealing and flash annealing treatments of cold-drawn as-quenched wires. Highest switching field, 1.3 Oe, and domain drive field, 0.5 Oe, for annealing temperature 330 C , time 30 min, axial tension 150 Kg/mm2and axial field 200 Oe are an order of magnitude improvement over the as-quenched (AQ) state. Corresponding induced peak voltage is 0.5 mV/turn with exciting sinusoidal field 2 Oe and 60 Hz. Shorter pulse generation elements (≈ 2 cm) than for AQ wires (≈ 6 cm) were realized with 0.5 mV/turn peak voltage. Maximum squareness ratio is close to unity, twice that of AQ (125 μm) wires.

Magnetic domain structure in amorphous glass-covered wires with positive magnetostriction

Experimental investigation of the domain structure in Fe/sub 77.5/Si/sub 7.5/B/sub 15/ amorphous glass-covered wires by Kerr microscopy is reported for the first time. A single domain configuration with axial easy axis was observed in glass-covered samples. After glass removal, a maze domain configuration appears at the wire surface, while the axially magnetized domain still exists within the wires inner region.

Mechanism of re-entrant flux reversal in Fe-Si-B amorphous wires

The mechanism of re-entrant flux reversal in Fe-Si-B amorphous wires is investigated by domain observation and reverse domain detection focusing on the magnetic properties near the wire ends. It is found that the wire consists of shell and core domains and that the core region has the residual reversing domain due to the demagnetizing field near wire ends in a remanent state. The residual domain is stabilized by forming a flux closure structure through the shell domain. This increases the threshold field for domain growth to a value much larger than the wall coercivity and results in predominantly re-entrant flux reversal. >