Toshio Tanuma

Exchange coupling in spin-valve structures containing amorphous CoFeB

(Co0.9Fe0.1)80B20/Cu/(Co0.9Fe0.1)80B20/Ni80Fe20/Fe50Mn50 spin-valve structures with a different Ni80Fe20 layer thickness were prepared by ion-beam sputtering. Varying the thickness of the Ni80Fe20 layer made it possible to control the exchange coupling between the Fe50Mn50 and amorphous CoFeB layers. When no Ni80Fe20 layer was inserted, the exchange coupling was responsible for increasing the coercivity of the a-CoFeB layers. With increasing Ni80Fe20 layer thickness, the biasing fields of the Fe50Mn50 layer increased from 0 to 125 Oe. The critical Ni80Fe20 thickness, above which the biasing effect was observed, was experimentally estimated to be 2 nm.

GIANT MAGNETORESISTANCE EFFECT IN MULTILAYERED WIRE ARRAYS

Three wire arrays, each comprised of a different type of giant magnetoresistive (GMR) multilayer, were fabricated by high‐resolution electron‐beam lithography and lift‐off techniques. With a GMR multilayer of the biquadratic‐coupling type, a magnetic field applied parallel to the wires produced a larger MR change and higher response than in the corresponding unpatterned multilayered film; however, the wire structures worsened the MR characteristics of two other types of GMR multilayers.

GMR In Corrugated Co/Cu Multilayers

A new corrugated material comprising antiferromagnetically coupled Co/Cu multilayers was prepared using V-grooved Si substrates. Scanning electron microscopy and X-ray diffraction observations indicate that the corrugated multilayers were successfully grown with the formation of smooth and clear interfaces. Magnetoresistance change with the sense current normal to the grooves was larger than that with the current parallel to the grooves. The MR enhancement due to the difference in measurement geometry increased as the width of the grooves decreased.

Physical properties of CoFe/IrMn spin-valves prepared using ion beam sputtering with an Xe-H2 mixture gas

Co90Fe10/Cu/Co90Fe10/Ir25Mn75 spin-valves with a Ta seed layer were prepared by ion beam sputtering. Improvements in magnetoresistive (MR) and magnetic properties were obtained by adding H2 to Xe sputtering gas. Specifically, the coercivity in the free Co90Fe10 layer considerably decreased as the H2 flow rate was increased. Furthermore, exchange coupling between the Ir25Mn75 and pinned Co90Fe10 layers became stronger in the preparation under the higher H2 flow rate. X-ray diffraction, transmission electron microscopy, and secondary ion mass spectroscopy observations suggest that micro-crystallization of each layer is responsible for improving the MR and magnetic properties.

Magnetoresistive characteristics of multilayered wire arrays

Wire arrays comprising three types of giant magnetoresistive (GMR) multilayers were fabricated by high-resolution electron-beam lithography and lift-off techniques. For antiferromagnetic coupling-type GMR multilayer, a magnetic field applied parallel to the stripes produced larger magnetoresistance (MR) change and a higher response than in corresponding multilayered film with no patterns. In contrast, the wire structures worsened the MR characteristics of different coercive fields-type and spin-valve-type GMR materials.

Steep MR change in NiFe/Cu/Co trilayers

A field sensitivity of about 2%/Oe in magnetoresistance (MR) change has been observed in NiFe(6 nm)/Cu/Co(5 nm) trilayers. The MR change was accompanied with a sharp increase in resistivity before decreasing steeply for increasing fields. Thickness of the Ca spacer layer influenced the sensitivity of MR change. These results suggest an existence of interlayer coupling between the two magnetic layers. An analysis of this MR effect suggests that biquadratic coupling plays an important role in the steep MR change.

Dependence of Magnetic Properties of Metal Evaporated Tape on O 2 Gas Flow Rate

Co-Ni films were evaporated on PET substrates with oxygen gas introduced into the chamber at various flow rates (0 ~ 300 ml), and its effects on the magnetic properties of the films were studied with its flow rate as a parameter. From the angular distribution of the film coercivity, two switching mechanisms seemed to exist in the film. They are 1) coherent rotation of the magnetization, and 2) domain wall motion. At higher O2 flow rates the former region tended to broaden, suggesting a finer columnar grain structure. The dependence of coercivities on temperature grew more marked at higher oxygen flow rates.