A. M. Zeltser

GMR multilayers and head design for ultrahigh density magnetic recording

This paper describes materials development, device modeling, and initial test results for a novel GMR reproduce head for ultrahigh density recoding (/spl sim/ 10 Gbit/in/sup 2/). It consists simply of a 20-bilayer GMR multilayer, self-stabilized by intrinsic antiferromagnetic interlayer coupling, and self-biased by sense current into a bipolar, field-gradient-sensing bias state. Analogous to a dual magnetoresistive (DMR) such a GMR-DMR head is capable of achieving very high linear resolution without shields. Tape-test results using evaporated NiFe/Cu and sputtered NiFeCo/Cu agree reasonably well with theoretical expectations. 1/f noise in these GMR multilayers will also be discussed.

Giant magnetoresistance in evaporated Ni‐Fe/Cu and Ni‐Fe‐Co/Cu multilayers

The magnetic and transport properties of electron‐beam evaporated (Ni83Fe17/Cu)10 and (Ni66Fe16Co18/Cu)10 multilayers were studied as a function of the Cu spacer, magnetic layer and Ta buffer layer thicknesses, as well as annealing conditions. All multilayers exhibited very small giant magnetoresistance (GMR) effect (<0.3%) in the as‐deposited state, however, after magnetic post‐annealing at 300–325 °C, GMR increased up to 4.5%–7%, depending on the multilayer type. In contrast to sputtered Ni‐Fe‐(Co)/Cu multilayers, GMR showed no oscillatory behavior as a function of Cu thickness. Similar to that reported in sputtered ‘‘discontinuous’’ Ni‐Fe/Ag multilayers, it is believed that Cu diffusion along the Ni‐Fe‐(Co) grain boundaries creates intra‐layer magnetic discontinuities in Ni‐Fe‐(Co) layers which promote inter‐layer antiferromagnetic coupling. The evaporated Ni‐Fe/Cu multilayers exhibited very low remanence, exceptionally low hysteresis, and quite uniform GMR properties through the thickness of the multi...

Thermal stability of CoFe, Co and NiFe/Co spin valves

The magnetotransport and magnetic properties of three types of spin valves containing CoFe and Co in the free and pinned layers were investigated as a function of annealing temperature. The microchemical changes induced by annealing were correlated with the evolution of spin valve properties. Auger depth profiling and X-ray diffraction revealed that excellent thermal stability up to 220/spl deg/C of the spin valves containing CoFe and Co can be attributed to an improvement in perfection of the as-sputtered, initially compositionally intermixed Co(Fe)/Cu/Co(Fe) and NiFe/Ta interfaces. The best overall thermal stability was exhibited by the 50Ta/20NiFe/30CoFe/23Cu/50CoFe/90FeMn/50Ta (layer thicknesses in /spl Aring/) spin valve. After annealing for 2 hours at 260/spl deg/C, it showed magnetoresistance ratio of 7.5%, exchange pinning field of 165 Oe, interlayer coupling field of /spl sim/11 Oe and easy axis coercivity of <4 Oe.

Structure and magnetic properties of FeRuGaSi multilayer thin films

The structure and magnetic properties of FeRuGaSi thin films used in very‐high‐frequency (150 MHz) recording head has been studied. The best soft magnetic properties, viz., coercivity of 0.2–0.3 Oe, permeability of 2000 at 1 MHz and 400–500 at 150 MHz, and magnetostriction of less than 10−6, were obtained after annealing at 450–500 °C. This magnetic behavior was attributed to the phase transformations and the increase in the grain size of the films occurring during the annealing process. Transmission electron diffraction revealed that B2 and/or DO3 ordered phases were formed in the films depending on the annealing temperature. However, good soft magnetic properties were associated with the formation of the B2 phase with low crystal anisotropy and saturation magnetostriction. These results are somewhat in contrast to what has been observed in Sendust, where magnetic softness is usually attributed to the formation of the DO3 phase.

Demixing in spin valve structures: an Auger depth profiling study

Abstract Two, NiFe/Co based spin valve structures, prepared by magnetron sputtering were studied by means of high-resolution Auger depth profiling. Strong interfacial mixing was found in the case of ‘as deposited’ specimens. A 2 h heat treatment at 260°C resulted in demixing, that is the width of interfacial mixed zone became less than that in the ‘as deposited’ condition.

Dependence of the interlayer coupling on anneal temperature in Ni–Fe/Cu evaporated multilayers

Resistivity and magnetization studies of [Ni83Fe17(27 A)|Cu(37 A)]10 multilayers, grown by electron-beam evaporation, reveal that the magnetoresistance (ΔR/R) increases from 100 μm) in-plane domains aligned antiparallel across the Cu layers. An increase in the magnetic scattering at low angles indicates that some of the remaining Ni–Fe moments are randomly oriented from one layer to the next.

Relationship between the structure and soft magnetic properties of FeRuGaSi films

The effect of annealing on the structure and magnetic properties (coercivity, saturation magnetostriction, and initial permeability) of (FeRu)x(GaSi) films (x=2.5, 3.4, and 3.9) sputtered on MnNi‐oxide and Li‐silicate glass‐ceramic substrates has been investigated. It is found that the best combination of soft magnetic properties (e.g., coercivity ≊0.3 Oe, permeability ≊1800 at 10 MHz, and magnetostriction < 1 × 10−6) is generally obtained after annealing between 450 and 500 °C independent of film composition, and subsequently deteriorate at higher annealing temperatures. This magnetic behavior is correlated with the crystal structure, grain size, and texture of the films as revealed by transmission electron microscopy and x‐ray diffraction. It is found that after annealing, all films exhibit best soft magnetic properties when they consist of mostly the B2 phase and their magnetic softness decreases with the formation of the DO3 phase.

Giant magnetoresistance studies in evaporated Ni–Fe/Cu and Ni–Fe–Co/Cu multilayers (abstract)

Room temperature giant magnetoresistance (GMR) and magnetic properties of (Ni–Fe/Cu)n and (Ni–Fe–Co/Cu)n multilayers were investigated. Alternating layers of Ni–Fe–(Co) and Cu were electron-beam evaporated in a computer-controlled high-vacuum system at base pressure of ⩽4×10−8 Torr and deposition rates of ⩽2 A/s. To complement and expand our previous investigation,1 GMR properties were additionally studied here as a function of cobalt content of Ni–Fe–Co films, the number (n) of bilayers, deposition temperature, and type of buffer layer. The Co content was varied from 7 to 17 at. %, and the number of bilayers ranged from n=8 to 20. No significant GMR was observed in the as-deposited multilayers. To produce tangible GMR, these multilayers were annealed between 300 and 360 °C for 2 h in a 150 Oe magnetic field in an argon atmosphere. The GMR effect (ΔR/R) was essentially independent of copper spacer thickness, which varied between 25 and 30 A. For Co containing multilayers the highest ΔR/R=7.6% was obtained...

Giant magnetoresistance in evaporated NiFe/Cu and NiFeCo/Cu multilayers (abstract)

The magnetic and transport properties of electron beam evaporated (Ni83Fe17/Cu)10 and (Ni66Fe16Co18/Cu)10 multilayers (ML) were studied as a function of the Cu spacer and magnetic layer thicknesses (tCu and tNiFe), annealing conditions and Ta buffer layer thickness. The ML were evaporated in a magnetic field at deposition rates ∼ 2 A/s and background pressure <5×10−8 mbar on Si/SiO2 substrates at Ts=200 °C. These ML exhibited two unique features: (1) ΔR/R and the interlayer coupling did not show oscillatory behavior as a function of tCu; and (2) after magnetic post annealing, ΔR/R increased from <0.3% in the as‐deposited state, to up to ∼6% and 7% in Ta/(NiFe/Cu) and (NiFeCo/Cu), respectively. The coupling between the NiFe layers changed from ferromagnetic in the as‐deposited state Mr/Ms∼0.9k;20 to essentially antiferromagnetic Mr/Ms<0.2) after appropriate annealing, and the ML became virtually isotropic in‐plane.This is quite different from strong oscillatory behavior of giant magnetoresistance (GMR) pre...

Soft magnetic properties of FeXGaSi (X=Ir, Rh) films

The soft magnetic properties and structure of FeGaSi based thin films containing up to 5.5 at.% Rh and 7.5 at % Ir were investigated. Films containing between 1.5 and 4.5 at.% Ir, after appropriate heat treatment, showed initial permeability of 1000-2000 at 10 MHz, and as high as 800 at 150 MHz, uniaxial anisotropy of 3-7 Oe, saturation magnetization > 14 kG, and thermal stability up to 550 degrees C. The Rh-containing films showed higher permeability at 10 MHz (2500-3000), similar saturation magnetization, but smaller uniaxial anisotropy ( >