Function Of Ni Thickness Research Articles

Supercurrent transmission through Ni/Ru/Ni synthetic antiferromagnets

Josephson junctions containing ferromagnetic materials are generating interest for use in superconducting electronics and cryogenic memory. Optimizing the performance of such junctions is an ongoing effort, requiring exploration of a broad range of magnetic systems. Here, we study supercurrent transmission through Ni/Ru/Ni synthetic antiferromagnets with the idea that their magnetic properties may be superior to those of isolated Ni layers. We find that the decay of the supercurrent as a function of Ni thickness is very slow with a decay length of 7.5 ± 0.8 nm. We also characterize the magnetic properties of the synthetic antiferromagnets as a function of Ni and Ru thicknesses.

Anomalous Supercurrent Modulation in Josephson Junctions With Ni-Based Barriers

We investigate the supercurrent transport characteristics of Ni-barrier Josephson junctions with various barrier multilayer structures. Our device fabrication and magneto-electrical measurement methods provide high enough statistics and rigor necessary for the detailed characterization of magnetic Josephson junctions. As a result, we obtain the oscillatory critical current as a function of Ni thickness that matches the clean-limit transport theory except for certain anomalous features. Salient details include the finite oscillation phase shift due to a nonmagnetic spacer, the near-zero effective magnetic dead layer, and the distorted current-phase relationship near the 0-π transition. These allude to intricacies in the microscopic transport that are unique to certain magnetic Josephson junctions. We discuss a route toward a comprehensive understanding of realistic magnetic Josephson junctions based on the underlying effect of exchange field on the superconducting spin modulation.

Large Interfacial Magnetostriction in (Co/Ni)4/Pb(Mg1/3Nb2/3)O3-PbTiO3 Multiferroic Heterostructures.

The magnetoelastic behavior of multiferroic heterostructures-coupling of magnetic anisotropy or domain dynamics to structural deformations-has been intensively studied for developing materials for energy-efficient, spin-based applications. Here, we report on a large, interface-dominated magnetostriction in (Co/Ni)4/Pb(Mg1/3Nb2/3)O3-PbTiO3 multiferroic heterostructures. Ferromagnetic resonance spectroscopy under voltage-induced strains enabled estimation of the saturation magnetostriction as a function of Ni thickness. The volume and the interface components to the saturation magnetostriction are (6.6 ± 0.9) × 10-6 and (-2.2 ± 0.2) × 10-14 m, respectively. Similar to perpendicular magnetic anisotropy in Co/Ni, the large, negative magnetostriction originates from the Co/Ni interfaces. This interfacial functionality delivers an effect over 300% larger than the bulk contribution and can enable low-energy, nanoelectronic devices that combine the tunable magnetic and magnetostrictive properties of Co/Ni multilayers with the ferroelectric properties of Pb(Mg1/3Nb2/3)O3-PbTiO3.

EFFECT OF THICKNESS ON THE STRUCTURAL, MICROSTRUCTURAL, ELECTRICAL AND MAGNETIC PROPERTIES OF Ni FILMS ELABORATED BY PULSED ELECTRODEPOSITION ON Si SUBSTRATE

We have studied the effect of thickness on the structural, microstructural, electrical and magnetic properties of Ni films electrodeposited onto [Formula: see text]-Si (100) substrates. A series of Ni films have been prepared for different potentials ranging from [Formula: see text]1.6[Formula: see text]V to [Formula: see text]2.6[Formula: see text]V. Rutherford backscattering spectrometry (RBS), X-ray diffraction (XRD), four point probe technique, atomic force microscopy (AFM) and vibrating sample magnetometry (VSM) have been used to investigate the physical properties of elaborated Ni thin films. From the analysis of RBS spectra, we have extracted the films thickness [Formula: see text] ([Formula: see text] ranges from 83[Formula: see text]nm to 422[Formula: see text]nm). We found that the Ni thickness, [Formula: see text] (nm), linearly increases with the applied potential. The Ni thin films are polycrystalline and grow with the [Formula: see text] texture. The lattice parameter [Formula: see text] (Å) monotonously decreases with increasing thickness. However, a positive strain was noted indicating that all the samples are subjected to a tensile stress. The mean grain sizes [Formula: see text] (nm) and the strain [Formula: see text] decrease with increasing thickness. The electrical resistivity [Formula: see text] ([Formula: see text]cm) increases with [Formula: see text] for [Formula: see text] less than 328[Formula: see text]nm. The diffusion at the grain boundaries may be the important factor in the electrical resistivity. From AFM images, we have shown that the Ni surface roughness decreases with increasing thickness. The coercive field [Formula: see text], the squareness factor [Formula: see text], the saturation field [Formula: see text] and the effective anisotropy constant [Formula: see text] are investigated as a function of Ni thickness and grain sizes. The correlation between the magnetic and the structural properties is discussed.

Structural and magnetic properties of Ni/Cu bilayers evaporated on CuZn substrate

In this present work we examine the effect of the Ni thickness t ( t ranges from 4 to 67 nm) and of the Cu underlayer (with t Cu = 27, 52 and 90 nm) on the structural and magnetic properties of Ni/Cu bilayers deposited onto CuZn substrate. The Ni films and the Cu underlayer have been deposited by thermal evaporation. The structural properties were derived from X-ray diffraction experiments. The texture, the strain B e and the grain size D are studied as a function of Ni thickness. The surface morphology is studied by means of a scanning electron microscope (SEM). The magnetic properties were studied by means of the vibrating sample magnetometer (VSM) and the magneto-optic Kerr effect (MOKE) technique in the longitudinal configuration. The coercive field, the squareness and the saturation field are investigated as a function of Ni thickness. All these results will be discussed and correlated.

Landauer theory of ballistic torkances in noncollinear spin valves

We present a theory of voltage-induced spin-transfer torques in ballistic noncollinear spin valves. The torkance on one ferromagnetic layer is expressed in terms of scattering coefficients of the whole spin valve, in analogy to the Landauer conductance formula. The theory is applied to Co/Cu/Ni(001)-based systems where long-range oscillations of the Ni torkance as a function of Ni thickness are predicted. The oscillations represent a novel quantum size effect due to the noncollinear magnetic structure. The oscillatory behavior of the torkance contrasts a thickness-independent trend of the conductance.

Anomalous Double Peak Structure in Superconductor/Ferromagnet Tunneling Density of States

We have experimentally investigated the density of states (DOS) in Nb/Ni (S/F) bilayers as a function of Ni thickness, d(F). Our thinnest samples show the usual DOS peak at +/- Delta(0), whereas intermediate-thickness samples have an anomalous "double-peak" structure. For thicker samples (d(F) > or =3.5 nm), we see an inverted DOS, which has previously only been reported in superconductor or weak-ferromagnet structures. We analyze the data using the self-consistent nonlinear Usadel equation and find that we are able to quantitatively fit the features at +/- Delta(0) -- in particular the thickness at which the inversion occurs -- only if we include a large amount of spin-orbit scattering in the model. Interestingly, we are unable to reproduce the subgap structure through the addition of any parameter(s). Therefore, the observed anomalous subgap structure represents new physics beyond that contained in the present Usadel theory.

Spin-mixing conductances of thin magnetic films from first principles

We present a first-principles theory of the spin-mixing conductance for a thin ferromagnetic film embedded epitaxially between two nonmagnetic metallic electrodes. The complex spin-mixing conductance is formulated as a linear response of the spin torque experienced by the film due to the spin accumulation in one of the electrodes. The derivation is based on nonequilibrium Green's functions; the obtained result for the torque response is in agreement with the response of spin fluxes on both sides of the ferromagnet as well as with expressions derived within the Landauer-B\"uttiker scattering theory. Numerical implementation of the developed formalism employs the tight-binding linear muffin-tin orbital method and calculations are performed for selected metallic and half-metallic ferromagnetic films relevant for spintronics applications. The spin-mixing conductance of the $\mathrm{Cu}∕\mathrm{Ni}∕\mathrm{Cu}(100)$ system is found to exhibit pronounced oscillations as a function of Ni thickness; their period is explained by spin-resolved Fermi-surface properties of nickel. Investigated half-metallic films include the full-Heusler ${\mathrm{Co}}_{2}\mathrm{Mn}\mathrm{Si}$ compound and the diluted (Ga,Mn)As magnetic semiconductors attached to nonmagnetic Cr(100) leads; the imaginary part of their spin-mixing conductance has a magnitude comparable to the real part. This unusual feature has been qualitatively explained in terms of a free-electron model.

Strong coupled superconductor in proximity with a quench-condensed ferromagnetic Ni film: A search for oscillatingTc

We present results of in situ transport and tunneling measurements on a quench-condensed (QC) Pb film covered by a QC ferromagnetic Ni layer. This experiment provides new evidence in the controversy over the existence of inhomogeneous superconductivity in a superconducting/ferromagnet $(S/F)$ system. The critical temperature of the superconducting Pb/Ni bilayer has been measured for numerous thicknesses of Pb ranging from 5 to 80 nm. No oscillatory behavior as a function of Ni thickness has been observed in the variation of ${T}_{c},$ implying no $\ensuremath{\pi}$ state in those bilayers. These results are interpreted in light of recent theoretical developments. Tunneling measurements of $(dI/dV)$ on Pb/Ni also show a monotonic depairing effect in the density of states of Pb versus the Ni thickness, which further confirms the absence of nonconventional superconductivity in this Pb/Ni system.

Perpendicular magnetic anisotropy in epitaxial Cu/Ni/Cu/Si (001)

We have deposited epitaxial Ni Cu bilayers and Cu/Ni/Cu trilayers on single-crystal (100) Si substrates in a molecular beam epitaxy chamber. The magnetic properties were studied in situ using magneto-optic Kerr effect measurements, and ex situ using vibrating sample magnetometry. The preferred direction of magnetization is perpendicular to the film plane across a broad region of Ni thickness. The thickness dependence of the anisotropy energy has been explained using the Néel pair interaction model and in terms of carefully characterized strains which are thickness-dependent due to misfit relaxation. We have observed misfit dislocations in these films using transmission electron microscopy and measured their average separation as a function of Ni thickness. Additionally, strain in the Ni layers has been measured as a function of Ni thickness using substrate curvature measurements. Using these results, we have calculated the value of the surface magnetic anisotropy term, which we have shown to be strain dependent.

Perpendicular magnetic anisotropy, domains, and misfit strain in epitaxial Ni/Cu1-xNix/Cu/Si (001) thin films.

We have investigated the magnetic anisotropy in epitaxial Ni/${\mathrm{Cu}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ni}}_{\mathit{x}}$/Cu/Si (001) thin films (0x50%) as a function of Ni thickness h and alloy substrate composition. Also the average in-plane biaxial strain ${\mathit{e}}_{0}$(h) in Ni/Cu (001) (x=0) was measured ex situ versus Ni thickness using optical interferometry. We observed that the preferred direction of magnetization is perpendicular to the films over an exceptionally broad Ni thickness range for films kept under UHV: 10 \AA{}h60 \AA{} in Ni/Cu (001); 20 \AA{}h40 \AA{} in Ni/${\mathrm{Cu}}_{60}$${\mathrm{Ni}}_{40}$/Cu (001). We have also studied the perpendicular magnetic anisotropy by magnetic force microscopy and observed a complex domain pattern characterized by two length scales and very strong contrast. We have analyzed our results using a phenomenological model that includes the bulk magnetoelastic anisotropy energy (${\mathit{B}}^{\mathit{b}}$${\mathit{e}}_{0}$) and both the surface magnetocrystalline (${\mathit{K}}^{\mathit{s}}$/h) and the surface magnetoelastic (${\mathit{B}}^{\mathit{s}}$${\mathit{e}}_{0}$/h) anisotropy energies. Our analysis yields the magnetic surface energies ${\mathit{K}}^{\mathit{s}}$ and ${\mathit{B}}^{\mathit{s}}$ of the vacuum/Ni (001) and Ni/Cu (001) interfaces. The origin of the strong perpendicular magnetic anisotropy lies in the surface energy ${\mathit{K}}^{\mathit{s}}$ corresponding to the Ni/Cu (001) interface and the bulk magnetoelastic anisotropy energy. The surface magnetoelastic anisotropy energy ${\mathit{B}}^{\mathit{s}}$${\mathit{e}}_{0}$ favors an in-plane magnetization. The effective magnetoelastic coupling coefficient depends strongly on h for h\ensuremath{\le}150 \AA{} and changes sign near h\ensuremath{\approxeq}28 \AA{}. The two observed in-plane to out-of-plane magnetization easy-axis transition thicknesses are predicted by our pheomenological model. The lower magnetization easy-axis transition is not due to the onset of misfit dislocations at the Ni/Cu interface.

Use of Magneto-Optic Kerr Effect Measurements to Study Strain and Misfit Accommodation in Thin Films of Ni/Cu (100)

ABSTRACTWe have detected magnetic transitions in Ni/Cu (100) films as a function of Ni thickness through in situ measurements of the magneto-optic Kerr effect (MOKE). Crystalline quality was monitored using in situ RHEED and Auger electron spectroscopy. Films were deposited by molecular beam epitaxy on silicon wafers and cleaved sodium chloride with varying epitaxial Ni layer thicknesses between 10 and 200 A. High-resolution TEM images of these films indicate decreasing misfit dislocation spacing and decreasing strain as measured by moiré fringe analysis with increasing Ni thickness. These observations have been correlated with changes in magnetic anisotropy as measured by MOKE. MOKE, therefore, may provide a tool for in situ monitoring of the kinetics of misfit accommodation in magnetic thin films.

Magnetization of very thin Ni films in epitaxial metal film sandwiches of Cu

Single-crystal nickel films varying in thickness from 2-40 Å were prepared by epitaxial growth between thicker layers (500 Å) of single-crystal copper (001). Their magnetization was measured as a function of field up to 10 kOe using a dc SQUID magnetometer. The saturation magnetization of these films was determined as a function of Ni thickness at liquid helium temperatures. A decrease in saturation moment from that of bulk nickel was observed for films of thickness less than 18 Å. The apparent Curie temperature also decreases with decreasing thickness for these films. The magnetization at maximum field as a function of temperature does not follow a Brillouin function.