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Notes: 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 Å/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 Å. For Co containing multilayers the highest ΔR/R=7.6% was obtained for 17 at. % Co deposited at 100 °C. The ΔR/R in all Ni–Fe–Co/Cu multilayers was sensitive to the deposition temperature, and R–H loops always showed significant hysteresis independent of the type of buffer layer. For application of these materials to very high density reproduce heads,2 the best results were obtained for (27 Å NiFe/25 Å Cu)14–18 multilayers deposited at 160 °C on 70 Å Ta buffer layer. For example, n=17 multilayers annealed at 350 °C exhibited ΔR/R=7.5%, half-width at half-maximum of ∼50 Oe, essentially no anisotropy, and virtually zero hysteresis (Fig. 1). Frequency dependent permeability measurements showed constant permeability between 10 and 200 MHz. Low- and high-angle x-ray diffraction as well as atomic force microscopy were used to investigate the effect of different geometries of multilayers on structure and roughness and to correlate them with GMR properties. © 1997 American Institute of Physics.

Notes: 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(ring)/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) previously reported in (NiFe/Cu) as-deposited ML made by ion-beam sputtering. After annealing at 300° and 325 °C for 2 h, the ΔR/R became ∼4.5% and ∼6.5% in (NiFe/Cu) and (NiFeCo/Cu) ML, respectively, and remained approximately constant for tCu=20 to 40 A(ring). The coupling field generally decreased with an increase in Cu and NiFe and after annealing at 300 °C dropped to as low as ∼25 and 45 Oe in (NiFe/Cu) and (NiFeCo/Cu) ML, respectively. The of ΔR/R Ta/(NiFe/Cu) ML increased with the thickness of Ta buffer layer from 30 to 70 A(ring). The high-angle θ–2θ x-ray scans of (NiFe/Cu) ML showed (111) texture, essentially independent of annealing temperature.The low-angle x-ray diffraction did not reveal roughening of the Cu–NiFe interfaces as a result of annealing. In many respects the GMR behavior of these ML is similar to that reported in sputtered "discontinuous'' NiFe/Ag. However, in contrast to the latter, the resistivity of NiFe/Cu monotonically increases with annealing temperature. This suggests that lattice interdiffusion is more prominent in the NiFe– system, consistent with a greater equilibrium compared solubility of Cu in the NiFe matrix compared to that of Ag. It is believed that Cu diffusion along the NiFe grain boundaries creates intra-layer magnetic discontinuity in NiFe and promotes inter-layer antiferromagnetic coupling between adjacent NiFe layers, which then gives rise to the observed GMR. Evaporated NiFe/Cu ML showed very small hysteresis and uniform GMR properties throughout the thickness, which makes them good candidates for GMR–DMR heads.©1996 American Institute of Physics.[S0021-8979(96)61508-X]

Notes: The magnetic age hardening produced by decomposition of a β-CoAl(B2) alloy has been studied by correlating the microstructure with the changes in magnetic properties during aging. A model based on coherent rotation has been developed to describe quantitatively the intrinsic coercivity of these fine-particle ferromagnets as well as the temperature dependence of the coercivity over the temperature range from 77 to 757 K. The model incorporates both magnetocrystalline anisotropy constants K1 and K2 in addition to the shape anisotropy of the elongated single-domain particles of metastable HCP cobalt which precipitate from solid solution during heat treatment. The magnetic properties of the particles are shown to depend critically on the crystallography of the solid-state transformation and particle morphology which were determined by transmission electron microscopy and diffraction.

Notes: 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.

Notes: 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.

Notes: Single and multilayer [111]-textured films of Permalloy and Cu were grown by molecular-beam epitaxy (MBE) on (111) Si substrates. The magnetic properties of the films were measured by ferromagnetic resonance and M-H loop tracer. The microstructure was observed by transmission electron microscopy, reflection high-energy electron diffraction, and x-ray diffraction. Even the single-layer films had lower easy axis coercivity Hce (≈0.6 Oe) and a lower in-plane anisotropy field (≈1.1 Oe) than permalloy films of similar thickness (≈80 nm) deposited by sputtering. In these single-layer films, the grain size and Hce both increased with improved pre-MBE cleaning of the Si substrate. The multilayers consisted of five identical thickness Permalloy layers separated by Cu interlayers. Multilayers with total magnetic thickness greater than 100 nm exhibited lower Hce than equivalent single-layer films. 4πMs, measured by a combination of ferromagnetic resonance and M-H loop tracer in very thin (〈5 nm) permalloy layers was found to drop off relative to the bulk value of 9.5 kG; a value of 5.0 kG was measured for a multilayer with 1-nm-thick Permalloy layers.