V. P. Nascimento

• Professor (Full) at Federal University of Espírito Santo

This work reports a room temperature study on the excitation of surface spin wave resonance (SWR) modes in magnetron sputtered NiFe/Zr multilayers. The surface anisotropy constants and the variations of the magnetization close to the surface of the ferromagnetic (FM) layers are deduced from ferromagnetic resonance (FMR) and SWR measurements at X-Ba...

Nb/Pt and Nb/Cu nanohybrids were sputtered on Si(100) substrate and systematically studied by transmission electron microscopy and magneto-transport measurements. Our experimental findings show that the colossal spin-valve effect measured in a hybrid formed by thick Pt layers deposited on Nb films is absent in equivalent Nb/Cu nanohybrids. In the l...

Ultrathin Si(100)/Ta/Ni80Fe20/Ir20Mn80/Ta heterostructure deposited by oblique incidence in a confocal magnetron sputtering exhibits an unexpected exchange bias effect, despite the rotation of the sample holder and absence of external magnetic field during the deposition. Its magnetic loops have anomalous shifts along the field axis, whose features...

Hybrid Nb(20)/Cu(5)/Py(2), Nb(20)/Cu(5)/Co(40) and Nb(20)/Cu(d\(_{Cu}\))/Py(2)/Cu(5)/Co(40) heterostructures (values in nanometers and d\(_{Cu}\) = 0, 2.5 and 5.0) were fabricated using a confocal DC magnetron sputtering setup. Performing magnetotransport measurements and using the anisotropic Ginzburg–Landau approach, the stray field values in zer...

A set of hybrid ferromagnetic/superconductor heterostructures was prepared by a confocal DC magnetron sputtering setup. The samples were systematically studied by measuring the magnetization and magneto-transport properties up to 2.5 T. The anisotropic behavior of the critical temperature, under applied magnetic fields, was investigated. For the Nb...

Non-collinear exchange couplings between Py and Co layers (0∘⩽φ⩽90∘) were achieved in Py(10)/Cu(5)/Co(10)/IrMn(8) (thickness values in nm) spin valves by modifying their layer morphologies using oblique deposition in a confocal sputtering setup. Two series of spin valves were prepared by keeping the sample holder fix during the depositions, except...

A modified magnetron sputtering setup was used to fabricate planar nanowire (NW) arrays of Co. The structural characterization of these polycrystalline Co NW arrays confirms the coexistence of both hcp and fcc phases, in which their relative fractions depend on the Co deposition time as well as the presence (or absence) of a bcc nanowire seed layer...

Ferromagnetic resonance (FMR) was applied to uncover the magnetic properties of NiFe/WTi multilayers, which showed themselves up as ideal candidates to exemplify the several resonance modes [optic, uniform, and interface FMR modes, volume and surface spin wave resonance (SWR) modes] that can emerge from the probing materials during the measurements...

Cathodic cage, operating in the plasma nitriding mode, has been widely applied to improve the mechanical properties of steel surfaces. This paper investigated the use of this method for the deposition of titanium nitride films on a glass substrate, demonstrating its promising application in nanostructured materials with good electrical and optical...

Chemical disorders in L21-B2-type structure, naturally occurred in ⁵⁷Fe-doped Ni50Mn36Sn14 pseudo-Heusler alloy or enhanced in milled material, were systematically investigated using local probe methods: ⁵⁷Fe Mössbauer spectroscopy (MS) and extended X-ray absorption fine structure (EXAFS). ⁵⁷Fe Mössbauer studies show two Fe configurations: paramagn...

Tungsten nanowires were deposited by DC magnetron sputtering onto vicinal sapphire substrates with a specific geometry in which the entrance angle (solid angle) of the vapor beam relative to the substrate was modified. Through 2D auto-correlation function analysis, suitable conditions to obtain a nanoscale corrugated surface with a high-order corre...

Structural and magnetic properties of the disordered and ordered Fe2MnAl Heusler alloys have systematically been investigated by local and bulk experimental methods. Plastic deformation, induced by cold-work, leads to a structural phase transformation from the ordered L21 to a disordered A2-structure, concomitantly with a change from paramagnetic P...

An experimental method was developed to set the magnetization direction in ferromagnetic layers of Si(100)/Cu/NiFe/Cu/Co/IrMn/Cu morphologically modified spin valves. Large uniaxial anisotropies emerged in the NiFe and Co layers due to modifications of their morphologies induced by the shadowing effect that arises from oblique depositions. Therefor...

Nb-films (thicknesses of 20 nm, 50 nm and 100 nm), directly grown on orientated Si substrates by DC sputtering, have shown reduced superconducting critical temperatures as compared to the bulk value; an effect associated with their disordered granular character (the disorder phenomenon of the Nb-films depresses the density of states at the Fermi le...

Hybrid Nb(tNb)/Co(10 nm)/IrMn(15 nm)/Nb(10 nm) heterostructured materials were prepared by DC Magnetron Sputtering and systematically studied by X-ray, magnetization and ferromagnetic resonance techniques. For thinner Nb buffer layer (≤10 nm), it was found that there is an inter-diffusion at Co/IrMn interface, which favors double-like hysteresis lo...

The magnetic profile of the Si(100)/NiO(35 nm)/NiFe(10 nm)/Ta(1 nm) sample has been obtained by X-ray absorption spectroscopy (XAS) and the X-ray magnetic circular dichroism (XMCD). Two experimental procedures were used. In the procedure 1, the magnetic depth profile has been determines using samples deposited with different NiFe thicknesses, Si(10...

The influence of the substrate temperature TS on the superconducting properties of 100 nm sputtered Nb films, prepared directly onto orientated Si (100) substrate, was systematically investigated by measuring their structural, morphological and magnetic properties. Within the TS interval 293–373 K no significant change is observed either in the Nb...

Magnetic properties of sputtered Gd thin films grown on Si (100) substrates kept at two different temperatures were investigated using X-ray diffraction, ac magnetic susceptibility, and dc magnetization measurements. The obtained Gd thin films have a mixture of hcp and fcc structures, but with their fractions depending on the substrate temperature...

Bulk and local magnetic properties of the polycrystalline -Fe2MnGa Heusler alloy have been studied using X-ray diffraction, magnetization measurements and zero-field and in-field Mössbauer spectroscopy. X-ray diffraction data indicate stabilization of a L12-type structure and no structural phase transformation in the temperature range 30–300 K. Whi...

Magnetic properties of sputtered NiFe/IrMn/Co trilayers grown on different seed layers (Cu or Ta) deposited on Si (100) substrates were investigated by magnetometry and ferromagnetic resonance measurements. Exchange bias effect and magnetic spring behavior have been studied by changing the IrMn thickness. As shown by X-ray diffraction, Ta and Cu se...

Magnetometry study of magnetron sputtered NiFe/IrMn/Co trilayers reveal that the exchange bias field at the NiFe/IrMn interface decreases with increasing NiFe layer thickness, up to 150 Å. At the IrMn/Co interface, a decrease also occurs when the NiFe layer thickness increases. Ferromagnetic resonance measurements at X and Q-band frequencies reveal...

The kinetics of formation of NiFe2O4 nanoparticles were investigated where the nanoparticles were produced by the proteic-sol-gel method using coconut water followed by annealing in (i) air, (ii) air in the presence of boron nitride (BN), or (iii) nitrogen. The sample dried at 473 K for 5.5 h was composed of small disordered NiFe2O4 nanoparticles i...

The influence of the chemical pressure on the magneto-structural properties of the Ni2MnGa Heusler alloy after a gradual substitution of Ga by Sn atoms was theoretical and experimentally studied in this work. Our data clearly show that an expansion of the L21-cell volume due Sn-substitution causes a diminution of the internal structural stress and...

Thin n-type ZnO films doped with different atomic concentrations of aluminium were grown by filtered vacuum arc deposition (FVAD) on glass substrates. The films were deposited using an oxygen working pressure of 2.0 mTorr with an arc current running at two 100 ms pulses s−1. Structural, optical and electrical properties were investigated to underst...

The effect of chemical disorder over the martensitic phase transformation of the Ni50Mn36Sn14 Heusler-type alloy was systematically investigated by performing X-ray diffractometry (DRX), DC magnetization and 57Fe-doping and 119Sn-Mössbauer spectroscopy measurements. DRX patterns are characteristics of a L21-type chemically disordered structure, whe...

The effect of high energy ball milling on the structural, magnetic and magnetocaloric properties of Ni50Mn36Sn14 Heusler-type alloy has been studied. X-ray diffraction results have revealed a reduction in the crystalline grain size concomitantly with defect inclusions in the crystalline lattice, favouring a chemical disorder effect that transforms...

The interfacial magnetism of NiO/NiFe bilayers with different NiFe layer thicknesses, produced by DC and RF magnetron sputtering, has been studied by magnetometry and X-ray magnetic circular dichroism (XMCD). In magnetic hysteresis loops, the exchange bias field was found to be inversely proportional to the NiFe layer thickness. The fit using the M...

The long-range interactions between the antiferromagnetic NiO(35 nm) and ferromagnetic NiFe(3 nm) layers across the Cr and Cu spacers have been studied by magnetization measurements and x-ray magnetic circular dichroism (XMCD). The strength of exchange bias coupling decays exponentially with the spacer thickness and extends up to 2 nm for Cu and 1....

We report studies by x-ray diffraction, ferromagnetic resonance (FMR), and x-ray magnetic circular dichroism (XMCD) in Co/Ru superlattices grown by magnetron sputtering. We studied the [ Co (50 Å )/ Ru (t_Ru)]₂₀ samples, which were deposited at room temperature on Si substrates with the Ru thicknesses, t_Ru , vary...

Gigahertz magnetoimpedance (MI) curves obtained in an exchange biased Ni81Fe19/Fe50Mn50 multilayer are reported. Experimental MI curves are shifted by the exchange bias field (HEB), following the features presented by the hysteresis curves. Theoretical MI curves, calculated using the classical expression for the impedance of a planar magnetic condu...

The interlayer exchange coupling (IEC) and the magnetic anisotropy of Co/Ru(0002) hcp superlattices, produced by magnetron sputtering, were studied by ferromagnetic resonance (FMR). The main mode and a secondary mode, with a higher resonance field, were identified in the perpendicular FMR spectra. The secondary mode is attributed to the resonance o...

We have studied the effect of roughness on the exchanged biased NiFe/FeMn/NiFe trilayers system. The samples were prepared under three different argon working pressures (2, 5 and 10mTorr) to obtain different roughness degrees. The root mean square roughness of the NiFe/FeMn interfaces enhances as the argon working pressure during the deposition inc...

X-ray reflectivity analyses were performed in the Si/WTi (7 nm)/NiFe (30 nm)/FeMn (13 nm)/NiFe (10 nm)/WTi (7 nm) exchange-biased system prepared by magnetron sputtering under three different argon working pressures. Layer-by-layer analyses were realized in order to obtain the interfacial roughness parameters quantitatively. For a fixed argon press...

The magnetism at the interfacial regions of the Fe50 Å /Cr27 Å 20 antiferromagnetic coupled multilayer was studied using the x-ray magnetic circular dichroism XMCD technique. Two experimental approaches were used to reach the interface regions. In the first one, multilayers of the same type, deposited with the Cr capping layer with different thickn...

We have studied the influence of an inserted nano-oxide layer (NOL) on the interfacial magnetism in spin-valve systems showing the giant magnetoresistance effect. Specifically, we performed a magnetic depth profile of these structures with and without a NOL, using the x-ray magnetic circular dichroism technique. We found that insertion of a NOL int...

A comparative ferromagnetic resonance (FMR) study of the magnetic properties of Si(100)[FeNi/Al/FeMn/Al]×10 and Si(100)[FeMn/Al(6 Å)/FeNi(30 Å)/Al]×20 multilayers is reported. Besides the uniform mode, the parallel and perpendicular FMR spectra of both multilayers also give evidence of additional magnetic phases in the films. The perpendicular FMR...

X-ray reflectivity and atomic force microscopy analyses were performed in the Si/WTi (7 nm)/NiFe (5 nm)/FeMn (13 nm)/WTi (7 nm) exchange-biased system prepared by magnetron sputtering. Layer-by-layer analyses were done in order to have interfacial roughness parameters quantitatively. X-ray reflectivity results indicate that the successive layer dep...

The ferromagnetic resonance (FMR) technique is used to study the exchange bias field in asymmetrical Ni Fe / Fe Mn / Ni Fe trilayers produced by dc magnetron sputtering under different working pressures. The FMR spectra give evidence of two resonance modes attributed to the two asymmetrical noninteracting NiFe layers. The study of the in-plane angu...

Structural and magnetic properties of Ni81Fe19/Zr multilayers, prepared by DC magnetron sputtering, were studied using X-ray diffraction, ferromagnetic resonance and magnetization. Low-angle X-ray diffraction results are typical of a modulated structure, while high-angle data suggest that the Ni81Fe19 layers can have amorphous or crystalline struct...

Structural and magnetic properties of nanocrystalline Fe0.67Co0.33 alloy prepared by high energy ball milling have been studied by x-ray diffraction and Mössbauer spectroscopy. The x-ray diffraction pattern of the sample milled for 160 hours indicates the existence of a single bcc phase. On the other hand, Mössbauer measurements, at different tempe...

Structural and magnetic properties of nanocrystalline Fe2Co and (Fe2Co)30Cu70 alloys prepared by ball milling have been studied by X-ray, Mössbauer and magnetization measurements. The X-ray and Mössbauer results of Fe2Co milled alloy indicate a formation of pure BCC phase with Bhf of 36T. Samples of (Fe2Co)30Cu70 alloys were prepared either by mill...

Structural and magnetic properties of nanocrystalline Fe2Co and (Fe2Co)0.30 Cu0.70 alloys prepared by high energy ball milling have been studied basically by x-ray, Mössbauer spectroscopy and magnetization measurements. For the Fe2Co alloy case, the Mössbauer measurements indicate that the sample with 160 hours of milling has two magnetic component...