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  1. 72 Acta Physica Polonica A

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  1. 7 Stobiecki F.

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  3. 5 Barnaś J.

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1
Content available remote

Superparamagnetic Grains as Source of Giant Magnetoresistance Effect in Discontinuous Co/Ag Multilayers

100%
Luciński T., Stobiecki F., Dubowik J., Czajka R.
Acta Physica Polonica A
|
1997
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vol. 91
|
issue 2
269-272
EN
The as-deposited and annealed Co/Ag discontinuous multilayer-like structures were examined. Discontinuous Co sublayers are thought to consist of fine superparamagnetic and ferromagnetic grains. Using the bimodal superparamagnetic grain sizes distribution the GMR(H) dependencies were successfully modelled with the use of two Langevin functions simulating the magnetization of the superparamagnetic grains.
2
Content available remote

Novel Mechanism of Biquadratic Coupling in Magnetic Superlattices

100%
Gruhn W.
Acta Physica Polonica A
|
1997
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vol. 91
|
issue 2
303-306
EN
Using the modified total energy approach of Bruno, we prove that for the transition metal or rare-earth superlattices the additional scattering of free electrons on magnetic ion multipole moment gives rise to ferroquadrupolar biquadratic coupling between magnetic layers. We show that in this novel, intrinsic mechanism, the anisotropy of the magnetoresistivity should manifest itself.
3
Content available remote

Giant Magnetoresistance in Permalloy/Copper Multilayers

63%
Luciński T., Stobiecki F.
Acta Physica Polonica A
|
1997
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vol. 91
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issue 2
273-275
EN
The oscillatory behaviour of the giant magnetoresistivity versus Cu sublayer thickness was observed in Ni_{83}Fe_{17}/Cu multilayers with an oscillation period of 1 nm independently of buffer layer and substrates used in the experiment. The giant magnetoresistance field sensitivity equal to 0.02%/Oe and 0.15%/Oe for the first and the second maximum respectively, were found. It was shown that the giant magnetoresistance effect in our multilayers is not only due to the antiferromagnetic coupling between adjacent permalloy layers but also due to the superparamagnetic-like behaviour related to the existence of the intermixed interfacial areas.
4
Content available remote

Interface Effective Pinning and Dynamical Coupling of Spin Waves in Bilayer Ferromagnetic Films with Canted Magnetizations

63%
Puszkarski H., Cottam M. G.
Acta Physica Polonica A
|
1991
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vol. 79
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issue 4
549-564
EN
We present a theory for the spin-wave excitations in bilayer magnetic systems with exchange coupling across the interface between two ferromagnetic films having the same crystallographic structure. The Hamiltonian includes exchange and anisotropy terms within each magnetic film of the composite system, as well as at the interface and at the free surfaces. We examine, in particular, the effect of interface canting between the magnetization directions for each film, and we derive effective pinning parameters and dynamic coupling parameters for the interface as functions of the canting angle. We show that, in the special case when the magnetization directions are antiparallel in the bilayer system, the two films may be considered as effectively decoupled as regards the spin-wave dynamics. We discuss the relevance of this theory to recent experimental studies of bilayer ferromagnetic systems that exhibit antiferromagnetic interface exchange.
5
Content available remote

Brillouin Zone Mapping of the Existence Conditions for Interface Bilayer Spin-Waves. Effects of the Configuration of the Film Magnetization

63%
Puszkarski H., Józefowicz R., Kołodziejczak B., Akjouj A., Djafari-Rouhani B., Dobrzynski L.
Acta Physica Polonica A
|
1996
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vol. 89
|
issue 5-6
675-688
EN
For the two interface cubic cuts: sc(110) and sc(111) we consider the existence regions of interface spin-waves of a ferromagnetic bilayer film on the two-dimensional Brillouin zone as to their size and shape versus the respective interface related parameters (interface exchange coupling and intrinsic interface anisotropy) applying the approximation of a very thick bilayer film and the method of Brillouin zone mapping (the three (100) interface cubic orientations have been dealt with earlier [Phys. Rev. B 51, 16008 (1995)]). Of particular interest to us still remains the emergence of interface spin-waves induced by varying dynamic quantities such as the in-plane propagation wave vector k_{∥}. Moreover, in our present investigation, we put especial emphasis on the effect exerted on the Brillouin zone mapping by varying (in the plane perpendicular to the film) the configuration angle 𝜗 of the film magnetization with respect to the film normal. We predict the existence of (at the most two) critical angles 𝜗_{c} at which the interface spin-waves emerge. These critical angles are functions of the in-plane wave vector k_{∥} of interface spin-wave propagation along the interface. Finally, we discuss the effects due to the presence of critical angles with a view to their exploitation in experimental measurements.
6
Content available remote

Interlayer Exchange Coupling: Effect of Alloying

63%
Kudrnovský J., Drchal V., Turek I., Šob M., Weinberger P.
Acta Physica Polonica A
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1997
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vol. 91
|
issue 1
15-25
EN
The effect of disorder in magnetic layers, in the spacer, and at interfaces between them on periods, amplitudes, and phases of oscillations of interlayer exchange coupling in magnetic multilayers is studied theoretically on the ab initio level. We employ the spin-polarized surface Green function technique within the tight-binding linear muffin-tin orbital method and the Lloyd formulation of the interlayer exchange coupling. The coherent potential approximation is used to describe the effect of alloying. The calculations are significantly simplified by employing the vertex-cancellation theorem. Numerical results illustrating the effect of various kinds of disorder in the system on the properties of the interlayer exchange coupling are presented.
7
Content available remote

Giant Magnetoresistance of [Ni_{80}Fe_{20}/Au/Co/Au]_{N} Multilayers Deposited on Flexible Substrates

63%
Gospodarczyk W., Urbaniak M., Stobiecki F., Szymański B.
Acta Physica Polonica A
|
2012
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vol. 121
|
issue 5-6
1234-1236
EN
Magnetic hysteresis and magnetoresistance of [Ni_{80}Fe_{20}/Au/Co/Au]_{10} multilayers displaying giant magnetoresistance and sputtered on a flexible polypropylene substrates (an adhesive tape) is investigated. The magnetoresistive properties are very similar to those found in films prepared under the same conditions on Si(100) substrates. It is demonstrated, too, that a bendability of the substrates can be utilized to form cylindrically shaped magnetoresistive sensors with reduced anisotropy of the effect.
8
Content available remote

Current-Induced Spin Accumulation and Spin Transfer Torque in a Néel Domain Wall

63%
Baláž P., Szymczyk Ł., Dugaev V., Barnaś J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1210-1212
EN
Current-induced spin accumulation in a domain wall and the associated spin torque exerted on the wall are analyzed theoretically. The considerations are limited to a relatively thick Néel domain wall in a bulk ferromagnetic metal. The current-induced spin density is calculated using the linear response theory and the Green function formalism.
9
Content available remote

Magnetic and Magnetoelectric Effects within a Sandwich Structure with the Parabolic Quantum Well

63%
Gruhn W.
Acta Physica Polonica A
|
2008
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vol. 113
|
issue 1
175-178
EN
We study magnetic effects in a trilayer formed of magnetic layers separated by a spacer with a parabolic potential profile. The focus is on mechanisms of indirect magnetic interactions within the spacer. We show existence of magnetic oscillations and novel type of magnetoelectric effect.
10
Publication available in full text mode
Content available

Néel's Magnetostatic Coupling in Sputtered Cu/Py/V/Py/MnIr/Cu Multilayers

63%
Urbaniak M., Brückl H., Stobiecki F., Luciński T., Reiss G.
Acta Physica Polonica A
|
2004
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vol. 105
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issue 3
307-313
EN
The correlation between magnetostatic or Néel's coupling and roughness of interfaces in sputtered Cu/Py/V/Py/MnIr/Cu multilayers was investigated with the help of atomic force microscopy and magnetometry. It is shown that the coupling strongly depends on the roughness of seed Cu layer which in turn depends on sputtering power. Roughness levels off after deposition of consecutive layers to about 0.2 nm rms.
11
Content available remote

Magnetization Curves of Geometrically Frustrated Exchange-Biased FM/AFM Bilayers

63%
Pankratova M., Žukovič M.
Acta Physica Polonica A
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2017
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vol. 131
|
issue 4
642-644
EN
We consider a ferromagnetic/antiferromagnetic bilayer on a triangular lattice in the framework of the classical XY model. The impact of the geometrical frustration in this system on the magnetization curves and the exchange bias phenomenon is studied. The magnetization curves and the phase diagram for such systems are obtained. We observe horizontal plateaus and a split of the hysteresis loop on the magnetization curves. It is shown that the shift of the hysteresis loop (exchange bias) occurs for the systems with a magnetically hard antiferromagnet.
12
Content available remote

Exchange Coupling and Magnetization Profiles of Binary and Ternary Magnetic Multilayers

63%
Süss F., Krey U., Krompiewski S.
Acta Physica Polonica A
|
1997
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vol. 91
|
issue 2
281-284
EN
Within a spin-polarized LMTO approach in the atomic-sphere approximation we calculate ab initio the magnetic properties of various binary and ternary multilayers composed of Fe, Co, Ni, Cr, V and Cu. The emphasis lies on the indirect exchange interaction of the magnetic sandwiches across the antiferromagnetic or non-magnetic spacers, and on the profiles of the intrinsic resp. induced magnetic moments. Among other results we find (i) that Ni is very sensitive on its neighborhood and that (ii) at the interface to Fe, V gets almost as strongly polarized as Cr, whereas in the interior layers, the V sandwich remains non-polarized.
13
Content available remote

Semiconductor Ferromagnetic Structures

63%
Story T.
Acta Physica Polonica A
|
2000
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vol. 98
|
issue 3
171-181
EN
Ferromagnetic semiconductor structures such as superlattices or trilayers form a new class of magnetic systems composed entirely of semiconductor materials. The examples are Ga_{1-x}Mn_{x}As-AlGaAs with the ferromagnetic layer of GaMnAs semimagnetic (diluted magnetic) semiconductor or EuS-PbS with the ferromagnetic member (EuS) of the family of europium chalcogenides. We discuss the spectrum of perspective ferromagnetic semiconductor materials, the effect of size and stress on magnetic properties of ultrathin semiconductor ferromagnetic layers, and the effect of interlayer exchange in all-semiconductor systems.
14
Content available remote

Lattice Misfit Strain as Origin for Biquadratic Interlayer Coupling

63%
Jaroszewicz R., Bąk Z., Gruhn W.
Acta Physica Polonica A
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1996
|
vol. 89
|
issue 3
421-424
EN
The direct observations of some MBE grown superlattices show large interfacial undulations, which is attributed to the elastic relaxation of tensile layers. Assuming that the interface lateral lattice deformation, due to ionic radii misfit, is given by the periodic solution of the Frenkel-Kontorova model, we calculate the magnetoelastic contribution to the biquadratic magnetic coupling between ferromagnetic layers across the nonmagnetic spacer. We show that due to the correlated modulations of the effective bilinear exchange integral, there arises a biquadratic exchange which favours perpendicular orientations of magnetization in adjacent ferromagnetic layers.
15
Content available remote

From the Co Nanocrystals to Their Self-Organizations: Towards Ferromagnetism at Room Temperature

63%
Lisiecki I.
Acta Physica Polonica A
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2012
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vol. 121
|
issue 2
426-433
EN
Here, we show that rather uniform 7 nm Co nanocrystals self-organize into long-range two- and three-dimensional superlattices. Due to this ability we have to control the mesoscopic ordering; unexpected intrinsic collective chemical and physical properties have been discovered. By annealing treatment, a crystallographic transition from a polycrystalline fcc- to single crystalline hcp-Co phase is obtained leading to a drastic change in the magnetic properties such as an increase in the blocking temperature that can reach a value close to room temperature. Neither coalescence between nanocrystals nor oxidation of the Co material is observed. In these artificial solids, when the individual nanocrystal anisotropy is low, super-spin glass behavior is observed.
16
Content available remote

RKKY-like Biquadratic Exchange in Magnetic Superlattices

63%
Gruhn W., Bąk Z., Jaroszewicz R.
Acta Physica Polonica A
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1996
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vol. 89
|
issue 3
417-420
EN
We show that in magnetic metallic superlattices along with the bilinear RKKY-reminiscent interaction between magnetic superlattices there can be an important quadrupole-quadrupole coupling. In an analytical way we derive the range functions of the quadrupol-quadrupole interaction and discuss its relation to magnetoresistivity.
17
Content available remote

Magnetisation and Hydrogenation of Mg/Ni Multilayers

63%
Pacanowski S., Marczyńska A., Dawczak-Dębicki H., Jabłoński B., Szymański B., Smardz L.
Acta Physica Polonica A
|
2018
|
vol. 133
|
issue 3
617-619
EN
In this contribution we have studied magnetisation of Mg/Ni multilayers (MLs) to characterise the alloing effect near interfaces. The layered structure was characterised by standard X-ray diffraction. The MLs were deposited by UHV magnetron sputtering onto naturally oxidised Si(100) substrates. Results showed, that due to Mg-Ni alloy formation near interfaces the magnetizations of the MLs were strongly reduced. Effective "dead" Ni layer thickness was estimated as 1.2 nm at room temperature (RT). Furthermore, hydrogen absorption kinetics at a pressure of about 1000 mbar was studied at RT in Pd covered Mg/Ni MLs using four-point resistivity measurements. Results showed that the fastest initial rise in resistance in the first 9 s was observed for d_{Ni}=3.5 nm.
18
Content available remote

Magnetic Mesoporous Silica Nanocomposite for Biodiesel Production

63%
Erdem S., Öksüzoğlu R., Avşar S., Erdem B.
Acta Physica Polonica A
|
2017
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vol. 132
|
issue 3
763-766
EN
Ordered mesoporous silicas can be utilized as support because of having large surface area, tunable porosity, uniform pore size distribution, high thermal stability and modifiable properties. However, these materials introduce separation problems in liquid-phase processes. We have prepared Fe₃O₄-SBA-15-SO₃H solid acid catalyst by combining the properties of a magnetic material and the mesoporous character of silica. The sulfonic acid functionalized solid acid catalyst, containing both magnetic nanoparticles and mesoporous silica, is not only separable but also stable under hydrothermal conditions, which are usually employed for biodiesel production. Esterification of oleic acid with methanol for biodiesel production was carried out effectively and 75% conversion of ester was approximately reached within six hours in the presence of Fe₃O₄-SBA-15-SO₃H magnetic solid acid catalyst. In addition, the catalyst could be separated from the reaction system by applying external magnetic field and reused without deactivation.
19
Content available remote

On Biquadratic Interlayer Coupling in Magnetic Multilayers

63%
Barnaś J.
Acta Physica Polonica A
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1994
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vol. 85
|
issue 2
461-464
EN
Intrinsic biquadratic interlayer coupling in magnetic layered structures is analysed theoretically within the spin-polarized free-electron approximation. The corresponding coupling parameter oscillates with the interlayer thickness with the oscillation period equal to half of that for bilinear term. An extrinsic mechanism following from a competition between the intra- and interlayer exchange coupling is also discussed.
20
Content available remote

Thermally Assisted Current-Driven Dynamics in Asymmetric Spin Valves

63%
Gmitra M., Barnaś J., Horváth D.
Acta Physica Polonica A
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2008
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vol. 113
|
issue 1
31-34
EN
Current-induced steady precessional modes in standard spin valves are usually excited as an interplay of spin-transfer torque, Gilbert damping, and external magnetic field. We propose an asymmetric spin valve, in which the spin current can excite stationary precessional modes also at zero external magnetic field. We also show that finite temperature can induce transitions between different dynamical modes. These transitions, in turn, lead to telegraph noise in magnetoresistance.
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