T. Luciński

Preparation and Characterization of Carbon Nano-Onion/ PEDOT:PSS Composites

Composites of unmodified or oxidized carbon nano-onions (CNOs/ox-CNOs) with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) are prepared with different compositions. By varying the ratio of PEDOT:PSS relative to CNOs, CNO/PEDOT:PSS composites with various PEDOT:PSS loadings are obtained and the corresponding film properties are studied as a function of the polymer. X-ray photoelectron spectroscopy characterization is performed for pristine and ox-CNO samples. The composites are characterized by scanning and transmission electron microscopy and differential scanning calorimetry studies. The electrochemical properties of the nanocomposites are determined and compared. Doping the composites with carbon nanostructures significantly increases their mechanical and electrochemical stabilities. A comparison of the results shows that CNOs dispersed in the polymer matrices increase the capacitance of the CNO/PEDOT:PSS and ox-CNO/PEDOT:PSS composites.

The influence of sublayer thickness on GMR and magnetisation reversal in permalloy/Cu multilayers

Abstract It has been shown that in Py/Cu (Py = Ni 87 Fe 17 , permalloy) multilayers obtained by face-to-face sputtering technology, two well-separated antiferromagnetically coupled ranges can be found centered at d Cu ≈ 1 and 2 nm, respectively. However, d Cu values corresponding to the largest field sensitivity of the GMR effect are different from those for which the strongest antiferromagnetic exchange coupling has been found. With decreasing Py thickness, the magnetic properties become strongly influenced by the magnetisation fluctuations. We attribute this effect to the presence of compositionally intermixed interfaces. Changes in the magnetic properties and magnetoresistance as a function of Py thickness are analysed in terms of evolution from paramagnetic through superparamagnetic to ferromagnetic behaviour of these intermixed regions.

Mössbauer study of the influence of thermal treatment on giant magnetoresistance and interface structure in Fe/Cr multilayers

The dependence of the giant magnetoresistance effect (GMR) on the interface structure in Fe/Cr multilayers was studied by magnetoresistivity and Mossbauer spectroscopy. The Fe/Cr multilayers consisting of Fe(6 nm)+[Cr(1.1 nm)/Fe(3 nm)]60+Cr(1.1 nm) were deposited by dc magnetron sputtering. Samples were annealed for 1 h at temperatures ranging from 200 to 500 °C. The interface structure was characterized by conversion electron Mossbauer spectroscopy (CEMS). Various different Fe sites: the bulk, step and perfect interface positions were identified. The evolution of the fraction of Fe atoms in different environments vs annealing temperature revealed that annealing at 300 °C induces bulk and in-plane diffusion of atoms. Higher annealing temperature causes substantial roughening of the interface related to a strong bulk diffusion of atoms. Microstructural changes observed in the CEMS spectra correspond well to the GMR measurements which reveal an enhancement of magnetoresistivity in Fe/Cr multilayers annealed...

Magnetic and Mössbauer study of Fe/Si multilayers

The magnetic and structural properties of Fe/Si multilayers (Mls) have been studied by x-ray diffraction (XRD) and conversion electron Mossbauer spectroscopy (CEMS) methods. Strong antiferromagnetic (AF) coupling J=−1.93 mJ/m2 accompanied by saturation field of 1.5 T has been found for Si layer thickness dSi=1.4 nm. Magnetic moment measurements of Fe/Si Mls vs Fe thickness revealed that 0.25 nm of Fe per single interface is magnetically inactive. The CEMS spectra recorded at room temperature consist of the Zeeman sextet characteristic of the pure Fe phase (hyperfine field of about 32.8 T) accompanied by two spectral components related to FeSi system: magnetic broad sextet and a quadrupole doublet. The broad sextet could originate from various Fe sites at the interface. The nonmagnetic quadrupole split (QS) doublet is most probably associated with the nonstoichiometric c-Fe1−xSix phase. For larger Si layer thickness (dSi>2 nm) the spectral contribution of the QS doublet increases from 5.7% to about 16%.

High sensitivity GMR with small hysteresis in Ni-Fe/Cu multilayers

Abstract Giant magnetoresistance (GMR) effect and magnetisation reversal processes have been investigated in Py/Cu(Py=Ni 83 Fe 17 , permalloy) multilayers (Mls) obtained by face-to-face sputtering method. The investigated films had constant sublayer thicknesses both for Py and Cu (d Cu =2 nm, d Py =2 nm) and various numbers of ferromagnetic sublayers. It has been shown that for such Mls a high field sensitivity of GMR effect (S≈0.4%/Oe) and negligible hysteresis can be obtained for a low number of Py layers.

Magnetoresistance study of Ni80Fe20/Co1/CuAgAu/Co2 asymmetric sandwiches

The (Ni(80)Fe(20i)Col);CuAgAu/Co2 asymmetric sandwiches have been examined for different sublayer thicknesses. Magnetoresistance, magnetooptical Kerr effect and alternating gradient magnetometry measurements showed that for 1.2 nm less than or equal to d(CuAgAu) less than or equal to 1.6 nm our trilayers are antiferromagneticatly coupled whereas for d(CuAgAu) greater than or equal to 1.9 nm the coupling between Ni80Fe20i Col and Co2 is ferromagnetic. The ferromagnetic coupling strength oscillates with CuAgAu thickness with a period of 1 nm. The appearance of the ferromagnetic interlayer coupling for d(CuAgAu) greater than or equal to 1.9 nm and its oscillatory character result from the interplay between RKKY-Iike exchange coupling and the magnetostatic orange-peel coupling. The values of the ferromagnetic coupling field between Ni80Fe20iCoI and Co2 for a constant CuAgAu thickness can be either enhanced or reduced depending on the ratio between Col, Co2 and Ni80Fe20 thicknesses. In spite of oscillatory ferromagnetic coupling strength for d(CuAgAu) greater than or equal to 1.9 nm our trilayers show the GMR amplitude of about 10% and the GMR field sensitivity of about 5%/Oe at room temperature being very promising from the application point of view

The concept of the existence of interfacial superparamagnetic entities in Fe/Cr multilayers

Giant magnetoresistance effects and their field dependence in Fe/Cr multilayer films prepared by rf magnetron sputtering have been modelled using the concept of the existence of paramagnetic regions at the Fe/Cr interfaces. The model has been applied to as-deposited and annealed samples with the result that the approximate sizes of superparamagnetic entities at the interfaces (or their magnetic moment) could be determined. The variation of the magnetoresistivity was studied as a function of annealing temperature. It has been demonstrated experimentally that the magnetoresistance follows the square of the magnetisation dependence for Fe/Cr multilayers.

On magnetic anisotropy in sputtered Co-Pd alloy films

Abstract This work presents the magnetic and electric investigation of Co-Pd thin films. It has been found that Co-Pd films obtained by the cosputtering method exhibit uniaxial anisotropy with the easy axis parallel to the plane of the film. The internal stress measurements showed the existence of the compressive stresses anisotropic in character.

Magnetoresistance studies of discontinuous multilayer thin Co/Ag films

Abstract Magnetoresistivity depending in an oscillatory way on d Ag has been found in wedged Co( d Co )/Ag( d Ag ) discontinuous multilayers. Two distinct maxima for d Ag = 1.1 and 2 nm have been observed. Simultaneously, a maximum in magnetoresistivity has been found for 80% Ag volume fraction. A decrease in the width of the magnetoresistance curves versus applied field was observed after annealing.

In situ monitoring of GMR and M(H) evolution during Co/Cu multilayers growth

The field dependencies of resistance and magnetic moment of the Co/Cu multilayers manifesting the GMR effect have been simultaneously examined in situ, during deposition process. The combination of these measurements with in situ thickness dependent resistance measurements allowed us to interpret the changes of the magnetic hysteresis loops. It has been shown that the all measured quantities can be presumably affected by the surface anisotropy.