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Research into annealing time effects on the microstructural evolution and consequent magneto-transport property changes in Ta/NiFe/CoFe/Cu/CoFe/PtMn/Ta spin valves is presented. It was found that the magnetoresistance and interlayer coupling field changes became large as annealing time rose.

We present the synthesis and magnetic properties of multifunctional CoPtAu alloy nanoparticles of three compositions, Co0.33Pt0.33Au0.33, Co0.2Pt0.2Au0.6, and Co0.4Pt0.4Au0.2, by a modified polyol process. The x-ray diffraction and transmission electron microscopy analyses confirm the formation of the alloy nanostructure comprising Au-rich and Pt-rich nanophases, with a narrow distribution of particle sizes and provides the detailed structural arrangements. The magnetic study shows the composition dependence of the magnetic properties of the nanoparticles, from superparamagnetic for both Co0.33Pt0.33Au0.33 and Co0.4Pt0.4Au0.2 to soft ferromagnetic for Co0.2Pt0.2Au0.6. [ABSTRACT FROM AUTHOR]

We investigated the spin wave dynamics of CoFeSiB film, which has a stripe domain structure at a low magnetic field region (<1 kOe). We measured the spin wave excitation spectra by employing Brillouin light scattering. Abnormal field dependence and dispersion relations were observed, and they are similar to spin wave quantization in laterally confined magnetic structures such as arrays of magnetic nanowires. The observed spin wave excitation spectra must be interpreted with spin wave quantization such as Damon–Eshbach mode separation. It was found that the spin wave quantization is related to the stripe magnetic domain structure in continuous film. The physical origin of the quantization is the partial reflection of the propagating spin wave at the periodic stripe domain boundaries. [ABSTRACT FROM AUTHOR]

We report the preparation and characterization of multifunctional AuFe alloy nanoparticles of three compositions, Au0.25Fe0.75, Au0.5Fe0.5, and Au0.75Fe0.25, by a polyol process. It is found that the fusion of the two elements into one nanostructure entity retains the optical and magnetic properties of the individual components. The x-ray diffraction and transmission electron microscopy analyses confirm the formation of the alloy nanostructure with a narrow distribution of particle sizes and provides the detailed structural arrangements. The magnetic investigation shows the superparamagnetic or soft ferromagnetic behavior of the nanoparticles at room temperature, whereas the UV-visible measurements display the variation of the absorption bands at ∼560 nm. The AuFe nanoparticles are rendered water soluble after thiolation. [ABSTRACT FROM AUTHOR]

Current-induced domain wall motion on a magnetic strip has been studied for its potential application to magnetic logic and memory devices. In this study, we carried out a series of calculations to investigate the changes of the domain wall velocity and width as a function of the notch shape using the Landau-Lifschitz-Gilbert solver. The domain wall had a uniform velocity when the notches were shallow and wide, while the width of the domain wall became narrow when the notches were deep and narrow. To produce a domain wall structure with both a uniform velocity and a narrow width, an asymmetric notch shape was devised. [ABSTRACT FROM AUTHOR]

We studied the effects of copper doping on the microstructure and magnetic properties of CoPt nanowires fabricated in anodized aluminium oxide (AAO) nanotemplates by electrodeposition. The morphological observation indicates well-formed CoPt and CoPtCu nanowires, while the structural analysis shows that fcc-Co3Pt phase exists prior to annealing and is retained in the doped nanowires, with minor hcp-CoPt phase postannealing. The doping causes shrinkage of the lattice spacing prior to annealing due to the insertion of smaller copper atoms. Compared to the undoped CoPt nanowires, the magnetic measurements reveal significant enhancement in the magnetic properties of the CoPtCu nanowire postannealing, resulting in the more rapid increase in the coercivity with annealing temperature. [ABSTRACT FROM AUTHOR]

Synthetic ferrimagnet-based spin-valve (SV) films comprising Ta 5/NiFe 2/IrMn 9/CoFe (P1) 1.5/ Ru 0.7/CoFe (P2) 3/Cu 2.8/CoFe 1.6/NiFe 3.2/Ta 5 (in nanometers) were examined with an emphasis given on understanding the interface evolution of IrMn/CoFe (P1) upon postdeposition annealing. A 300 °C, 5 h annealing resulted in 12% and 42% decreases in effective pinning field and 29% and 53% decreases in MR ratio for the bottom (B) and top (T) SV, respectively. Because both structures exhibit different thermal degradation behaviors, we were curious to uncover the underlying causes by employing various analytical methods. The column sizes of the B--SV and T--SV were about 30 and 15 nm, respectively. No major difference in the (111) crystal texture was observed. We found that the main cause was due to the interlayer diffusion of atomic constituents such as Mn, most likely through grain boundaries and IrMn/CoFe interface, where the degree of the diffusion was considerably higher for the T--SV. Due to the surface free energy differences depending on the deposition sequence, two types of SV structures behaved differently upon exposure to annealing. The B--SV featuring less grain boundaries and nonabrupt IrMn/CoFe (P1) interface could effectively impede interlayer diffusion and, as a result, exhibited less thermal degradation in MR properties. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions comprising amorphous CoNbZr layers have been investigated. Co[SUB85.5]Nb[SUB8]Zr[SUB6.5] (in at.%) layers were employed to substitute traditionally used Ta layers with an emphasis given on understanding underlayer effect. The typical junction structure was SiO[SUB2]/CoNbZr or Ta 2/CoFe 8/IrMn 7.5/CoFe 3/Al 1.6 + oxidation/CoFe 3/CoNbZr or Ta 2 (nm). For both as-deposited state and after annealing, the CoNbZr-underlayered structure showed superior surface smoothness up to the tunnel barrier than Ta-underlayered one (0.16 vs 0.34 nm). Ultrasmooth layer structure was proven beneficial for reducing temperature-dependent magnetoresistance properties. A longer annealing degraded the properties most likely due to Mn interdiffusion toward the bottom ferromagnetic electrode as confirmed by Auger electron spectroscopy. By a slight change in the bottom electrode thickness (CoNbZr 4/CoFe 10), the tunneling magnetoresistance ratio can be increased up to 32% after 10 min annealing at 300 °C. [ABSTRACT FROM AUTHOR]

We introduce amorphous CoNbZr-based spin-valves (SVs) where CoNbZr substituted Ta layers that have been traditionally used for under and capping layers. The purpose of this study was to investigate thermal stability of the new structure at elevated temperatures. A comparison was also made with a similarly structured Ta-based SV. Magnetoresistance (MR) ratio and exchange bias field (H[sub ex]) of CoNbZr-based SV increased up to about 50% (from 4.5% to 6.8%) and 52% (from 294 Oe to 448 Oe), respectively, after annealing at 300 °C for 240 min. The root-mean-square (rms) surface roughness values for CoNbZr and Ta single layers were 0.07 nm and 0.43 nm, respectively, indicating that an amorphous CoNbZr offers much smoother surface than the Ta layer. Because CoNbZr-based SVs possess fine and dense microstructures, they were able to resist interdiffusion at elevated temperature, resulting in an improvement in thermal stability. In addition, Mn diffusion into the pinned CoFe layer might be reduced probably due to the fact that CoNbZr capping layer provided almost equal chemical potential for Mn diffusion into the pinned CoFe layer. [ABSTRACT FROM AUTHOR]

In the present study, an emphasis was given on elucidating the details of microstructural changes in both undoped FePt and Zr-doped FePt films upon exposure to postdeposition annealing. Recently, the present authors have discovered [S. R. Lee, S. Yang, Y. K. Kim, and J. G. Na, Appl. Phys. Lett. 78, 4001 (2001)] that 3 at. % Zr doping into Fe[sub 59]Pt[sub 41] films accelerated the ordering kinetics (10 min at 500 °C), accompanying high coercivity H[sub c] of 7.3 kOe. Our transmission electron microscopy study on both Fe[sub 59]Pt[sub 41] and [Fe[sub 59]Pt[sub 41][sub 97]Zr[sub 3] films annealed at 500 °C for 60 and 10 min, respectively (both exhibited H[sub c] = 7300 Oe) revealed that the FePtZr film displayed excellent microstructural features: smaller average grain size (D) with narrower distribution (σ) (D = 6.0 nm, σ = 2.3 nm) compared with FePt (D = 33.6 nm, ρ = 25.0 nm). For the FePtZr system, we have found that an ordered phase decomposed into disordered phases (thereby losing the high H[sub c]) after 15 min annealing. By evaluating the long-range-order parameter S changes, we speculate that the cause of the disordering was primarily due to the formation of a Pt-Zr compound. [ABSTRACT FROM AUTHOR]

Giant magnetoresistance (MR) and effective exchange coupling field (H[sub ex]) variations in bottom-type synthetic ferrimagnet based spin-valve (B-SV) films consisting of sputter-deposited Ta 5/seedlayer (NiFe, Cu, or Ru) 2/IrMn 9/CoFe (P1) 1.0-1.5/Ru 0.7/CoFe (P2) 3/Cu 2.8/CoFe 1.6/ NiFe 3.2/Ta 5 (in nanometers) multilayers have been investigated. In particular, a focus was given on understanding the magnetotransport changes when the thickness difference between P2 and P1 layers, Δt(=t[sub P2]-t[sub P1]), was varied. These results were compared with those from similarly structured top spin-valve (T-SV) samples. When characterizing the subpeak profiles of MR transfer curves, we found that the subpeak shape of a B-SV with Δt=1.5 (= 3.0-1.5) nm was different from that of a T-SV with the same At but was remarkably similar to that of a T-SV with Δt=2.0 (= 3.0-1.0) nm. The degree of interfacial mixing (estimated to be in the order of 0.5 nm) during deposition at IrMn/CoFe (P1) appears higher for the B-SV: this resulted in an increase in effective Δt (or a decrease in effective P1 thickness). Hence, the effective thickness difference (Δt[sub eff]) caused by intermixing has to be considered for designing B-SV structures. Annealing also induced changes in subpeak profiles, H[sub ex], and MR ratios resulting from interdiffusion. In overall, a B-SV consisting of a NiFe seedlayer exhibited higher thermal stability than others. [ABSTRACT FROM AUTHOR]

Magnetic properties of electrodeposited CoNiFeS films were studied to seek their feasibility for applications in microelectromagnetic devices such as high areal density recording heads. We started with NiFe and then expanded experiments to a CoNiFe system. Finally, we added a fourth element, sulfur, to further improve physical properties. A small amount of sulfur inclusion has induced grain size refinement and offered magnetic softness to the film accompanying with increased electrical resistivity. Grain size was found to be in the order of 10 nm. Co[sub 73]Ni[sub 17]Fe[sub 9]S[sub 1] (in wt. %) films with thickness of 2.5 μm exhibit superior properties compared with currently utilized Ni[sub 45]Fe[sub 55]: high saturation magnetic flux density (B[sub s]∼17 kG), low coercivity (H[sub c]∼0.4 Oe), near zero saturation magnetostriction (λ[sub s]∼1.0×10[sup -6]), high permeability (μ∼1300 at 100 MHz), and high electrical resistivity (ρ∼55 μΩ cm). From a processing standpoint, we were able to control film thickness uniformity by adjusting current distributions between the auxiliary electrode and cathode across 100 mm wafers. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]