Function Of Co Layer Thickness Research Articles

Strong interfacial Dzyaloshinskii–Moriya induced in Co due to contact with NiO

The magnetic properties of NiO/Co/Pt as a function of Co layer thickness were investigated by polar magneto-optical Kerr effect (PMOKE) (magnetometry and microscopy) and Brillouin Light Scattering (BLS) spectroscopy. PMOKE measurements revealed strong surface anisotropy (1.8 mJ/m2) favoring perpendicular magnetic anisotropy and asymmetric domain wall propagation explained by anticlockwise chirality. BLS measurements show that this chirality is induced by strong interfacial Dzyaloshinskii–Moriya interaction (+ 2.0 pJ/m). This is one of the highest values reported so far for Co layers surrounded by different layers. The observed chirality is opposite to what has been found in Co/oxide interfaces. These results and data published earlier, indicate that the strength of interfacial Dzyaloshinskii–Moriya interaction increases with the amount of stoichiometric NiO. Therefore, this work shows that NiO is the source of the interfacial Dzyaloshinskii–Moriya interaction.

Investigation of local structural and magnetic properties of discontinuous to continuous layer of Co at Co/MgO interface in MgO/Co/MgO trilayer structure

We investigate influence of oxygen migration in MgO/Co/MgO trilayer structure by varying Co and MgO layer thickness. To resolve Co/MgO interface structural and magnetic properties, we used near edge X-ray absorption spectra (XANES), X-ray absorption fine structure (XAFS) spectroscopy and Magneto-optical Kerr effect (MOKE) on MgO/Co/MgO trilayer structure. O K-edge XANES spectra show the variation in hybridization of Co 3d orbitals with neighboring O 2p orbitals as a function of Co layer thickness. Co L3 -edge XANES and Co K-edge XAFS results revealed the quantity of CoO formation as a function of Co layer thickness from discontinuous layer to continuous layer. Formation of cobalt oxide is mainly due to island formation of Co ≤ 10 nm layer and oxygen migration from MgO layer at interface via redox reaction to form CoO bonds. The oxygen migration is driven by imperfect stoichiometry of MgO at the Co/MgO interface. The formation of CoO layer influences the CoO orbital hybridization modifying in-plane magnetic anisotropy as a function of Co and MgO layer thickness. Higher coercivity (Hc) for lower thickness of Co layer confirms the formation of domain wall pinning. A model has been drawn to describe the interaction of Co layer with MgO layer at Co/MgO interface from discontinues to continuous region of Co thin film of magnetic tunnel junctions (MTJ)s, which may help to design high-performance spintronic devices.

Magnetic behavior of superconductor/ferromagnet superlattices

A study of the electromagnetic response of superconductor/ferromagnet $\mathrm{Nb}∕\mathrm{Co}$ superlattices is presented. The dc magnetization is measured as a function of Co layer thickness, applied field ${H}_{a}$, and temperature. For very thin Co layers, no ferromagnetism is detected and the observed response is essentially that of a collection of uncoupled Nb layers. When the Co layer is thick enough for ferromagnetism to be established, prior to the field-cooled magnetization measurements, the Co layers are magnetically saturated in the parallel or antiparallel directions to ${H}_{a}$. In this case, the magnetic response of the otherwise uncoupled Nb layers is found to depend on both ${H}_{a}$ and the stray fields.

Microstructure and magnetic properties of Ti/Co/Ti films

The two series of asdeposited and annealed Ti/Co/Ti thin films were deposited by magnetron sputtering onto glass substrates at room temperature. The structural and magnetic properties of the films at room temperature were investigated as function of Co layer thickness. X-ray diffraction (XRD) profiles show Co nanograins are formed as the hexagonal-close-packed (hcp) structure. The perpendicular coercivity of the Ti(15 nm)/Co(30 nm)/Ti(15 nm) film annealed at 450 °C for 30 min is about 288 kA·m −1.

Ferromagnetic resonance study of polycrystalline cobalt ultrathin films

We present room-temperature ferromagnetic resonance (FMR) studies of polycrystalline ∥Pt∕10nmCu∕tCo∕10nmCu∕Pt∥ films as a function of Co layer thickness (1⩽t⩽10nm) grown by evaporation and magnetron sputtering. FMR was studied with a high-frequency broadband coplanar waveguide (up to 25 GHz) using a flip-chip method. The resonance field and the linewidth were measured as functions of the ferromagnetic layer thickness. The evaporated films exhibit a lower magnetization density (Ms=1131emu∕cm3) compared to the sputtered films (Ms=1333emu∕cm3), with practically equal perpendicular surface anisotropy (Ks≃−0.5erg∕cm2). For both series of films, a strong increase of the linewidth was observed for Co layer thickness below 3 nm. For films with a ferromagnetic layer thinner than 4 nm, the damping of the sputtered films is larger than that of the evaporated films. The dependence of the linewidth can be understood in terms of the spin-pumping effect, from which the interface spin-mixing conductance is deduced.

Current-Induced Excitations in Single Cobalt Ferromagnetic Layer Nanopillars

Current-induced excitations in Cu/Co/Cu single ferromagnetic layer nanopillars ( approximately 50 nm in diameter) have been studied experimentally as a function of Co layer thickness at low temperatures for large applied fields perpendicular to the layers. For asymmetric junctions current-induced excitations are observed at high current densities for only one polarity of the current and are absent at the same current densities in symmetric junctions. These observations confirm recent predictions of spin-transfer torque induced spin-wave excitations in single layer junctions with a strong asymmetry in the spin accumulation in the leads.

Growth of fcc Co in sputter-deposited Co/Au multilayers with (1 1 1) texture

The growth of Co/Au multilayers on Si(0 0 1)/SiN x is investigated by means of transmission and high resolution electron microscopy (TEM-HREM) as a function of Co layer thickness. Although there is an amorphous SiN x buffer layer between the substrate and the multilayer, the growth of alternative Co and Au layers exhibit strong texture with the (1 1 1) planes of Au oriented normal to the growth direction. The multilayer consists of columns that are composed of small misoriented crystals and multiple twins having as twin planes the (1 1 1) planes of growth. Electron diffraction analysis shows that when the Co layers are thinner than the Au layers an average face centred cubic (fcc) lattice is formed throughout the columnar structure of the multilayer, adopting an interplanar d-spacing of 0.229 nm along the growth direction. When the Co layer thicknesses become equal or greater than Au thickness then two separate cubic lattices appear due to internal stress relaxation.

Oscillation phenomenon of transition temperatures in Nb/Co and V/Co superconductor/ferromagnet multilayers

T c oscillation phenomenon of Nb/Co and V/Co superconductor/ferromagnet multilayers has been observed as a function of Co layer thickness d Co. Spontaneous magnetization appeared for d Co≳7 Å in both Nb/Co and V/Co systems. T c exhibited double minimum oscillations with the first local minimum at ∼12 Å for Nb/Co and at ∼18 Å for V/Co and with the second local minimum at ∼32 Å for both systems. The first minimum may be caused by a combined effect of magnetic spin-flip scattering, resonance scattering by Co virtual levels in the interfacial region and thickness dependent exchange field. The second minimum is found to be consistent with the appearance of so-called π-phase.

Structural, magnetotransport, and optical properties of sputtered Co/Cu multilayers examined as a function of Co layer thickness at the second antiferromagnetic maximum

A series of {[Co(tCo)/Cu(2.1 nm)]30/Co(tCo)}30 multilayers have been deposited under specific magnetron sputtering deposition conditions that lead to giant magnetoresistance (GMR) curves with technological interest. X-ray reflectivity, magnetic, magneto-transport, and spectroscopic ellipsometry measurements were used together to examine the dependence of their properties upon the Co layer thickness (tCo). Remarkably, the obtained film density and roughness, the saturation and coercivity fields, the reduced remnant magnetization, the GMR ratios, and the plasma frequency exhibit a significant divergence as a function of tCo in the range between 1.3–1.6 nm. The observed microstructural, magneto-transport, and magnetic relative differences, induced in (111) textured Co/Cu multilayers by varying the tCo, were correlated with changes of the optical electronic states of the constituents in the electronic density of states near the Fermi level.

Dependency of coercivity on Co layer thickness in Co/Cu multilayer structures

The magnetic and structural properties of Co/Cu multilayered film structures were studied as a function of Co layer thickness to determine the interrelationship between coercivity and ferromagnetic layer thickness. The nominal compositions of the films are NiFe(50 /spl Aring/)/Cu(2500 /spl Aring/)/[Co(t)/Cu(50 /spl Aring/)]x, where t=7, 10, 25, 50, 100 /spl Aring/ for x=20, and t=200, 400, and 2000 /spl Aring/ for x=10, 5, and 1, respectively. The measured coercivity correlates strongly with the changes in the local structural properties of the Co layers. Values were found to decrease with increasing t for t<200 /spl Aring/ in response to the decreasing effect of surface and interface domain wall pinning. For t/spl ges/200 /spl Aring/ coercivity values increase corresponding with the increased magnetocrystalline anisotropy associated with a transition in the Co layer from an fcc state to an hcp state.

Structure and Magnetic Properties of Electrodeposited Cobalt/Platinum Multilayers

Structure and magnetic properties of electrodeposited Co/Pt multilayers were studied as a function of Co-layer thickness. The multilayers were prepared by a dual cell technique under potential control. The structure of the multilayers was characterized by transmission electron microscopy (TEM). The interface of the electrodeposited multilayers was mixed owing to electrochemical reactions, and there was no preferred orientation along the growth direction. The compositionally modulated structure was demonstrated by the Bragg peaks of low angle X-ray diffraction, but the quality of the interface was low. These Bragg peaks were not found in the specimens with Co-layer thickness less than 1 nm because of the interface alloying. The easy magnetization axis of these electrodeposited multilayers lay in plane, and no perpendicular anisotropy was observed. These results indicate that structure and magnetic properties are different from those prepared by physical vapor deposition (PVD).

Magnetic anisotropies of ultrathin Co(001) films on Cu(001).

We present experimental evidence that ferromagnetic order at room temperature in ultrathin epitaxial Co(001) layers on Cu(001) substrates is stabilized by in-plane magnetic anisotropies. All relevant anisotropy contributions have been determined as a function of Co layer thickness with and without an additional Cu overlayer.

Magnetic and structural properties of Co/Cr multilayers with in-plane anisotropy

Previously we studied the effect of Cr spacer layer on in-plane coercivity in Co/Cr multilayered films. It was found that the high coercivity is related to the easy axis in-plane orientation and the character of the composition modulation. In this paper, the dependence of the saturation magnetization as a function of Co layer thickness is used to study the interface structure. The layer structure is confirmed by small angle x-ray diffractometry for typical films. The magnetic interaction among the grains is studied by examining deviation from the behavior predicted by the Wohlfarth model for noninteracting single-domain particles.

Temperature and thickness dependence of unidirectional magnetic anisotropy effects in Co/CoO thin films

We have studied the temperature and thickness dependence of the exchange-induced unidirectional anisotropy field ( H s ) and coercive field (Δ H c ) in Co/CoO bilayers using a Faraday balance. Results show that H s and Δ H c decrease monotonically with increasing temperature vanishing around T crit ∼ 210 K, which is distinctly lower than the Néel temperature of bulk CoO (289 K). The unidirectional exchange anisotropy field shows the predicted proportionality to the inverse of the ferromagnetic layer thickness. We have observed that the temperature dependence of H s can be described by (1− T/T crit) n , where n is a linear function of Co layer thickness.