Nonmagnetic Alloys Research Articles

Electrodeposition of NiP Film used as a Nonmagnetic Spacer in Laminated (CoFe/NiP)n Writer Pole

Electrodeposition of NiP film used as a thin nonmagnetic spacer in laminated multilayer (2.4T CoFe/NiP)n perpendicular writer pole is described. The electrodeposition of laminated multilayers was carried out in a dual-bath automated electroplating tool. The thin NiP films with thicknesses from 2.0 to 20 nm were obtained as nonmagnetic amorphous alloys with P-content higher than 18 at%. The problem of a concentration gradient at the CoFe/NiP interface, i.e. a lower P-content in the NiP deposit within a distance of 10 nm from the CoFe-interface, was solved by using STI-1 Proprietary organic additive in the plating solution. The details of the electrodeposition of NiP films and their properties are described.

Head-to-SUL Spacing Reduction With a Magnetic Seed Layer and the Effect on Perpendicular Recording Characteristics

A new underlayer structure consisting of a magnetic seed was used to reduce the recording layer-to-soft magnetic underlayer (RTS) spacing and its effect on perpendicular recording characteristics was investigated. The RTS spacing is reduced by partially replacing the non-magnetic FCC NiW alloy layer with a magnetic CoNiFe layer that acts as a part of the underlying SUL through magnetic exchange coupling. Magnetic CoNiFe layer promotes predominant FCC (111) planes of NiW layer that enhances epitaxial growth of the subsequent Cr BCC (110), Ru and Co HCP (0002) layers. As a result of improved crystallography with magnetic seed, the Co (0002) c axis dispersion is reduced at lower RTS spacing. The head write-ability becomes stronger at lower RTS spacing and the influence of side fringing fields on the nearest adjacent track erasure is highly dependent on the write head type at different RTS spacing. In addition, the change in RTS spacing also affects the read-back response. The signal-to-media noise (SNRm) is improved at low linear densities regardless of RTS spacing but degrades at higher linear densities when RTS spacing becomes too low. It is important to optimize the RTS spacing and the head-to-media integration to improve overall system performance.

Aleksandr Pavlovich Gulyaev: founder of a school of classical metals science

The works of A. P. Gulyaev performed at MAI, TsNIITMASh, and TsNIIchermet and devoted to various aspects of theoretical and applied metals science are analyzed. Professor T. F. Volynova, a disciple of Gulyaev, a Doctor of Engineering, an active member of the New York Academy of Sciences since 1995, heads the Laboratory for Problems of Metals Science created by Gulyaev. In the encyclopedic edition of “WHO IS WHO IN RUSSIAN METALLURGY” of 1999 she is included in the list of leading Russian specialists in the field. Her interests cover creation of new classes of multifunctional materials, high-strength nonmagnetic, damping, and antifriction alloys, and wear-resistant tool and structural materials for general and special engineering.

Model for magnetic–nonmagnetic binary alloys

AbstractAn extension of a mean‐field approximation (MFA) developed within standard basis operators (SBO) is used to study magnetism in magnetic–nonmagnetic binary alloys. The Curie temperature is calculated from the free energy within the framework of the present approach. The calculated results are in fair agreement with the theoretical results of other research groups for the same problem but utilizing other methods. Finally, the case of NiPt alloys is briefly examined as an example test for the comparison with experiment. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Evolution of the magnetic properties ofCo2MnGaHeusler alloy films: From amorphous to ordered films

We have investigated the evolution of the structural ordering and the crystal structure of polycrystalline ${\mathrm{Co}}_{2}\mathrm{Mn}\mathrm{Ga}$ Heusler alloy (HA) films and the structural effect on their magnetic properties. It is shown that the chemical and the structural ordering can be changed by the postannealing temperatures from an amorphous to more ordered structures typical for the HA. The magnetic properties of the films also depend strongly on the postannealing temperature. The as-deposited amorphous ${\mathrm{Co}}_{2}\mathrm{Mn}\mathrm{Ga}$ films show a weak ferromagnetic behavior due to the presence of a small amount of relatively highly magnetized regions in the nonmagnetic alloy matrix. Low-temperature (up to $513\phantom{\rule{0.3em}{0ex}}\mathrm{K}$) annealing of the amorphous films results in the formation of a mixture of ${\mathrm{Co}}_{2}\mathrm{Mn}\mathrm{Ga}$ and metastable $ϵ\text{\ensuremath{-}}{\mathrm{Mn}}_{3}\mathrm{Ga}$ and/or ${\mathrm{Mn}}_{3}{\mathrm{Co}}_{7}$ phases and causes a substantial increase in both magnetic moment and resistivity. Annealing at higher temperatures (up to $753\phantom{\rule{0.3em}{0ex}}\mathrm{K}$) leads to a structural order of $A2∕B2$ type. The amorphous $\ensuremath{\rightarrow}A2$ $(B2)$ structural transformation in ${\mathrm{Co}}_{2}\mathrm{Mn}\mathrm{Ga}$ films induces an increase of about 30% in the alloy resistivity, qualitative changes in the shape of magneto-optical spectra, and an increase in the magnetic moment per f.u. up to $(2--2.5){\ensuremath{\mu}}_{B}$. These results are discussed in terms of the band structure of the alloy. The best ${\mathrm{Co}}_{2}\mathrm{Mn}\mathrm{Ga}$ films, deposited on heated $(753\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ substrates, exhibit the $B2$ (or $L{2}_{1}$) structure and nearly the bulk value of magnetization of $3.5{\ensuremath{\mu}}_{B}$.

Magnetic and transport properties of the giant-unit-cell Al 3.26Mg 2 complex metallic alloy

The β-Al 3Mg 2 complex metallic alloy comprises about 1168 atoms in the giant-unit cell, making this material excellent candidate to investigate how the exceptional structural complexity and the coexistence of two different length scales – one defined by the unit-cell parameters and the other by the cluster substructure – affect physical properties of a metallic material. We have investigated magnetic, electrical, thermal transport and thermoelectric properties of a monocrystalline and a polycrystalline Al 3.26Mg 2 sample in a mixed β–β′ phase, grown by the Czochralski technique. Electrical resistivity is in the range ρ ≈ 30–40 μΩ cm and exhibits T 2 dependence at low temperatures and T at higher temperatures, resembling nonmagnetic amorphous alloys. Magnetic susceptibility χ measurements revealed that the samples are Pauli paramagnets with significant Landau diamagnetic orbital contribution. The susceptibility exhibits a weak increase towards higher temperature. Combined analysis of the ρ( T) and χ( T), together with the independent determination of the Pauli susceptibility via the NMR Knight shift suggests that the observed temperature dependence originates from the mean-free-path effect on the orbital susceptibility. The electronic density of states (DOS) at the Fermi energy E F was estimated by NMR and was found to amount about 90% of the DOS of the fcc Al metal. Thermal conductivity contains electronic, Debye and hopping of localized vibration terms, whereas the thermopower is small and negative. High structural complexity of the β-Al 3Mg 2 complex metallic alloy does not result in high complexity of its electronic structure. We found no evidence for the existence of a pseudogap in the DOS at E F.

Nitinol stenting and an unsuccessful surgical operation

Stent implantation in vascular access for haemodialysis has grown up in the last few years. Nine percent of percutaneous transluminal angioplasties (PTA) performed in 2001 on haemodialysis accesses was associated with stent implantation, according to the United States Renal Data System 2003 annual data report [1]. Furthermore, graft longevity is improved when stenoses are treated with stents in selected cases [2,3]. Among several materials, nitinol is one of the most used: it is a non-magnetic alloy of nickel (ni) and titanium (ti) (þ nol, from Naval Ordinary Laboratory, where it was created in 1968) [4]. We report here the case of a haemodialysis patient bearing a native arteriovenous fistula (AVF), in whom nitinol stents behaved as a two-faced Janus: initially, nitinol stent implantation in a stenotic vein enabled the patient to overcome a syndrome of venous hypertension; after 1 year, when surgical ligation of the AVF was decided upon because of the relapse of the syndrome, the same nitinol stents represented an unexpected trap.

Electrochemistry and surface investigations of anodically passivated layer formed on Fe–Mn–Al–Cr alloy in Na2SO4 solution

Electrochemical anodic passivation of Fe–24Mn–4Al–5Cr non-magnetic alloy in 1 mol L−1 Na2SO4 solution has been used to modify the corrosion resistance of the alloy. The improved corrosion resistance of the Fe–24Mn–4Al–5Cr alloy was investigated by electrochemical measurement in 1 mol L−1 Na2SO4 solution, and by Auger electron spectroscopy/X-ray photoelectron spectroscopy (AES/XPS) analyses. As the anodic aging time in 1 mol L−1 Na2SO4 solution increases from 15 min to 5 h at a potential of 620 mV(SCE), the potential decay time from the passive to active state in 1 mol L−1 Na2SO4+0·5 mol L−1 H2SO4 solution increases from ∼230 to ∼2800 s the decay time also increases with more negative anodic aging potential. Anodic polarisation measurements in 1 mol L−1 Na2SO4 solution show that performance the passive current density of the anodically passivated layer decreases while its corrosion potential increases, to values superior to those of 1Cr13 stainless steel. The Al and Cr contents are enriched and the Fe and Mn contents are simultaneously depleted within the anodically passivated layer formed in 1 mol L−1 Na2SO4 solution. The effect of anodic passivation aging on the structure and chemical state, and corresponding corrosion resistance of the anodically passivated layer mainly depend on the anodic aging time, anodic aging potential and oxidising power of the electrolyte.

Mössbauer study of ultrathinFe∕Almultilayer films

Multilayers of Fe (between 0.3 and $2.0\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ thickness) separated by a $3.0\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ thick Al spacer were prepared by vacuum evaporation and were then investigated by $^{57}\mathrm{Fe}$ M\"ossbauer spectroscopy measurements between 4.2 and $300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ and in various external magnetic fields. Mixing of the components at the interface was studied by transmission electron microscopy. The formation of a nonmagnetic Al-Fe interface alloy is verified by a detailed analysis of the low temperature M\"ossbauer spectra. The effective thickness of the Fe layers was deduced from the amount of the nonmagnetic component and it was found to be correlated with the shape of the Fe hyperfine field distribution. A marked change of the temperature and of the external magnetic field dependence of the Fe hyperfine fields were observed as a function of the effective layer thickness. The hyperfine field component attributed to two monolayer thick Fe regions decreases linearly with increasing temperature; it disappears at well below room temperature and it is hardly influenced by external fields up to $7\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. The formation of three and more monolayer thick regions with increasing effective thickness results in an approach to the bulk behavior, ${T}^{3∕2}$-temperature dependence, and smaller magnetic anisotropy.

Development of a Piston-Cylinder Pressure Cell using Nonmagnetic and High-Yield Strength Alloys for a SQUID Magnetometer

A piston-cylinder pressure cell for a commercial SQUID magnetometer (Quantum Design) has been developed by using nonmagnetic and high-yield strength alloys. The cell allows us to achieve pressures of 2.2 GPa at room temperature and 1.7 GPa at low temperatures. We have measured magnetization of paramagnetic palladium and superconducting lead placed within our cell and have estimated that a magnetization of over 2 ×10 -3 emu is possible to measure within the NiCrAl cell as absolute accuracy. As a demonstration of the cell, the paramagnetic susceptibility of pressurised Ca 2 RuO 4 under 1.5 GPa is shown.

Theory of the residual resistivity of dilute alloys of nonmagnetic 3d–5d transition metals

The residual resistivity of dilute alloys of nonmagnetic transition metals is calculated by the kinetic equation method with allowance for the two-band character of the conduction at low impurity concentrations. It is shown that for all dilute nonmagnetic binary alloys of the substitution type the value of the residual resistivity is a linear function of the square modulus of the off-diagonal s-d matrix element of the scattering T-matrix.

Volume expansion contribution to the magnetism of atomically disordered intermetallic alloys

The origin of magnetism in atomically disordered transition-metal--nonmagnetic (i.e., FeAl) alloys has been investigated by dichroism and diffraction measurements at high pressure and by band structure calculations. The results show that, in contrast to earlier studies, besides the effects of the local environment of the magnetic ions, disorder-induced lattice changes play a key role in the magnetic properties of these systems. We demonstrate experimentally and theoretically that about 35--45% of the magnetic moment of ${\mathrm{Fe}}_{60}{\mathrm{Al}}_{40}$ alloys arises from lattice expansion effects induced during the disordering process. Such large effects in ${\mathrm{Fe}}_{60}{\mathrm{Al}}_{40}$ could actually be related to the moment-volume instability observed in these alloys.

Electrical, magnetic, thermal and thermoelectric properties of the “Bergman phase” Mg 32(Al,Zn) 49 complex metallic alloy

The Mg–Al–Zn system of intermetallics contains an exceptional crystalline phase Mg 32(Al,Zn) 49, named the Bergman phase, whose crystal structure is based on a periodic arrangement of icosahedral Bergman clusters within the giant-unit-cell, so that periodic and quasiperiodic atomic orders compete in determining the physical properties of the material. We have investigated electrical, magnetic, thermal and thermoelectric properties of a monocrystalline Bergman phase sample of composition Mg 29.4(Al,Zn) 51.6, grown by the Bridgman technique. Electrical resistivity is in the range ρ ≈ 40 μΩ cm and exhibits positive-temperature-coefficient with T 2 dependence at low temperatures and T at higher temperatures, resembling non-magnetic amorphous alloys. Magnetic susceptibility χ measurements revealed that the sample is a Pauli paramagnet with a significant Landau diamagnetic orbital contribution. The susceptibility exhibits a weak increase towards higher temperature. Combined analysis of the ρ( T) and χ( T), together with the independent determination of the Pauli susceptibility via the NMR Knight shift suggests that the observed temperature dependence originates from the mean-free-path effect on the orbital susceptibility. The electronic density of states (DOS) at the Fermi energy E F was estimated by NMR and was found to amount 72% of the DOS of the fcc Al metal, with no evidence on the existence of a pseudogap. Thermal conductivity contains electronic, Debye and hopping of localized vibrations terms, whereas thermopower is small and negative. High structural complexity of the Bergman phase does not result in high complexity of its electronic structure.

Nickel silicon thin film as barrier in under-bump-metallization by magnetronsputtering deposition for Pb-free chip packaging

In the search for a Pb-free compatible under-bump-metallization (UBM) barrier material, magnetron sputtering of a nonmagnetic nickel silicon alloy (NiSi) target was used to deposit a low-stress polycrystalline NiSi thin film. In the reaction with SnAg3.0Cu0.5 solder, NiSi was found to have greatly reduced reaction and intermetallics (IMC) formation rates compared with sputtered NiV. A continuous layer of IMCs in NiSi UBM-solder joint remains stable after 10 reflows and 1000 h thermal aging tests, resulting in preferred bulk solder failure mode in ball shearing/pull testing. Our results demonstrate that NiSi is a highly promising thin film barrier material suitable for Pb-free solder bumping.

Fabrication and Magnetic Properties of Ternary Alloy Co—Ni—Pb Nanowire Arrays.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Anomalous vibrational effects in nonmagnetic and magnetic Heusler alloys

First-principles calculations are used in order to investigate phonon anomalies in non-magnetic and magnetic Heusler alloys. Phonon dispersions for several systems in their cubic L2$\mathrm{_1}$ structure were obtained along the [110] direction. We consider compounds which exhibit phonon instabilities and compare them with their stable counterparts. The analysis of the electronic structure allows us to identify the characteristic features leading to structural instabilities. The phonon dispersions of the unstable compounds show that, while the acoustic modes tend to soften, the optical modes disperse in a way which is significantly different from that of the stable structures. The optical modes that appear to disperse at anomalously low frequencies are Raman active, which is considered an indication of a stronger polarizability of the unstable systems. We show that phonon instability of the TA$_{2}$ mode in Heusler alloys is driven by interaction(repulsion) with the low energy optical vibrations. The optical modes show their unusual behavior due to covalent interactions which are additional bonding features incommensurate with the dominating metallicity in Heusler compounds.

Residual electrical resistivity in dilute nonmagnetic alloys of transition metals

The residual electrical resistivity in dilute alloys of nonmagnetic transition metals is calculated within Mott's two-band model without using the electron-impurity interaction as a small parameter. The linear dependence between reduced residual electrical resistivity and square of modulus of the nondiagonal element of the scattering T matrix is found for row transition metals dilute alloys. Experimental and calculation results are compared.

Fabrication and Magnetic Properties of Ternary Alloy Co–Ni–Pb Nanowire Arrays

Abstract Ferromagnetic–nonmagnetic heterogeneous ternary alloy Co–Ni–Pb nanowire arrays having composition, Co, 15 atom%; Ni, 45 atom%; Pb, 40 atom%, were successfully fabricated by alternating current (AC) electrodeposition into nanoporous alumina templates. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) observations revealed that the Co–Ni–Pb nanowries were polycrystalline with uniform diameters of around 20 nm and lengths up to several micrometers. Magnetic measurements showed that the coercivity of the samples increased with the annealing temperature up to 550 °C and reached a maximum (1020 Oe).

Magneto-optical properties of Co∕Ge(100) with ultrathin Ag buffer layers

Magnetic properties of Co films (<2nm) with Ag buffer layers (<0.7nm) grown on Ge(100) at room temperature and 200K were studied by surface magneto-optical Kerr effect. Without the buffer, the films reveal in-plane magnetic anisotropy even Co and Ge forms nonmagnetic interfacial alloys. The hysteresis due to intercalation of Ag can be detected at thinner Co thicknesses. The buffer can effectively cutoff the intermixing of Co and Ge. As the thickness of Ag is reduced, out-of-plane magnetic anisotropy due to the interface interactions between Co∕Ag and Co∕Ge was discovered and was only at 200K.

Efficiency of magnetic liposomal transforming growth factor‐beta 1 in the repair of articular cartilage defects in a rabbit model

We evaluated the efficacy of a magnetic liposomal delivery system of transforming growth factor (TGF)-beta(1) in the treatment of articular cartilage defects in a rabbit model. Articular cartilage defects were created in the patellar groove of rabbits, and a permanent magnet or a nonmagnetic alloy was implanted in the defect site. Magnetic liposomal drugs, prepared by the conventional film method and sonication, were injected into the defect site 1 week after surgery. First, the efficacy of the magnetic liposomal delivery system was evaluated by using a model compound fluorescence-labeled dextran 40,000 (FD-40). Then, the therapeutic efficiency of magnetic liposomal TGF-beta(1) was evaluated by cartilage histological scoring at 4, 8, and 12 weeks after surgery. The injected magnetic liposomal FD-40 accumulated at the target site where a permanent magnet had been implanted. The histological score showed that the injection of magnetic liposomal TGF-beta(1) under magnetic force was significantly effective in the repair of the defect site over 12 weeks after surgery. Injection of TGF-beta(1) into the cartilage defect was effective as a magnetic liposomal preparation under magnetic force, resulting in acceleration of the cartilage repair, probably because of the desirable accumulation of TGF-beta(1) at the target site.