Yousuke Irie

Spin-Valve Memory Elements Using [{Co-Pt/Cu/Ni-Fe-Co}/Cu] Multilayers

A new type of magnetoresistive memory using spin-valve multilayers composed of semi-hard magnetic layers and soft magnetic layers separated with nonmagnetic layers was developed. The fabricated memory element was composed of a word line of Au film and a magnetoresistive sense line of [{CoPt/Cu/NiFeCo}/Cu]N multilayers. This spin-valve memory has nonvolatile and nondestructive readout properties.

Magnetoresistance in CoMnB/Co(Fe)/Cu/Co(Fe) spin-valves

Abstract Magnetoresistance in AM/M′/Cu/M spin-valves was studied, where AM = CoMnB or CoNbZr and M′,M = Co or CoFe. M′ is a thin magnetic layer interposed between an AM and a Cu layer to enhance the MR ratio, and M is a magnetic layer having a larger H c than the AM layer. A considerably large MR ratio, 7.6%, with small switching field was obtained for the spin-valves with AM = CoMnB and M′(=M) = Co. Surface oxidation of the M layer was effective in increasing the saturation field of the spin-valves. These spin-valves are very thin (≤10 nm) and are advantageous for MR heads having narrow shield gaps.

Spin-valve multilayers of [H/Cu/S] (H Co, CoPt, or CoFe, S NiFeCo) and memory cells

Abstract Spin-valve memory elements composed of hard and soft magnetic layers separated with non-magnetic layers have been developed. Non-destructive read out (NDRO) is possible with this memory device as the hard magnetic layer is used for the data storage and the magnetization switching of the soft magnetic layer is used for the data readout. Spin-valve multilayers having small saturation fields have been studied for the memory elements.

HIGH SENSITIVITY IN MAGNETORESISTANCE OF EPITAXIAL NIFE/CU/CO (/CU) (100) SUPERLATTICES

Noncoupled‐type [NiFe/Cu/Co(/Cu)] single‐crystal‐like superlattices were prepared on Si/Cu(100) substrates using ultrahigh vacuum evaporation. Si/Cu (5 nm)/[Co (3 nm)/Cu (6 nm)/NiFe (3 nm)/Cu (6 nm)]×10 multilayers showed 6.1% magnetoresistance(MR) change with 2 kA/m of applied field, which is much higher sensitivity than those of poly‐crystalline films. Furthermore, placing a thin Ag layer (0.2 nm) at the midpoint of a Cu layer improved the MR sensitivity of the epitaxialfilm. Sandwich‐type Si/Cu (5 nm)/NiFe (10 nm)/Cu (2.4 nm)/Ag (0.2 nm)/Cu (2.4 nm)/Co (10 nm) superlattice showed sharp switching characteristics of the MR curve between lower and 4.3% higher resistivity. These epitaxialfilms showed biaxial anisotropy in the film plane with easy axes of [011] and [011] directions. The higher MR sensitivity in the epitaxialfilms may originate in the square‐shaped magnetization curves along the easy axes [011] and [011] of the Co layers. Flatness of interface was also effective to improve the MR sensitivity of the films.

Oscillations in Magnetoresistance in Epitaxial (100) and (111) NiFe/Cu Multilayers

Multilayers (MLs) of NiFe/Cu with (100) and (111) orientation were epitaxially grown on Si(100)/Cu and Si(111)/Ag/Cu substrates, respectively. The RKKY-like oscillations of magnetoresistance ratios were observed in the epitaxial NiFe/Cu MLs with the Cu spacer layer thickness (t Cu). The (100)-oriented NiFe/Cu MLs showed maxima at t Cu=0.9, 1.6, 2.0 and 2.5 nm, while the (111)-oriented MLs showed maxima at t Cu=0.9 and 1.9 nm.

The Magnetic Properties of Metallic Multilayers Prepared by UHV Evaporators

The MR (magnetoresistance) characteristics of metallic multilayer films are reported to be dependent on the method of preparation. Co/Cu multilayer films were prepared using a UHV evaporator. The MR characteristics were compared with those of sputtered films. Co/Cr multilayer films showed small-angle X-ray diffraction peaks and a large MR ratio of 15% at room temperature. However, NiFeCo/Cu multilayer films did not exhibit small-angle X-ray diffraction peaks, and their MR ratios were less than 2% at room temperature.

Magnetoresistance in metallic multilayers

MR (Magnetoresistance) characteristics of metallic multilayers such as [M/X(JMPC)] and spin-valve multilayers such as [{Fe-Mn/M/X/M}/X] were studied, where M=Ni-Fe-Co. Co-Fe… and X=Cu. [Co/Cu] showed large MR ratios, but the saturation fields, Hs, were large. [Ni-Fe-Co/Cu] showed considerably large MR ratios and small Hs and are applicable for MR sensors. Spin-valve multilayers showed sharp and very small transient fields and are suitable for electro-magnetic devices that require low field operations.