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1
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Transport and Magnetoresistance in Low Carrier Density Ferromagnets

100%
Littlewood P.
Acta Physica Polonica A
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2000
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vol. 97
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issue 1
7-13
EN
In metallic magnets, scattering from magnetic fluctuations above and near T_{C} may provide a substantial contribution to the electrical resistance ρ(T). However, this effect is usually small because the dominant fluctuations are near q ≈ 0, which does not produce substantial backscattering across the Fermi surface unless 2k_{F} is itself small; such a situation can be realised in metallically-doped ferromagnetic semiconductors. A simple adaptation of the theory of deGennes and Friedel shows the low field magnetoresistance scales with the ratio of field induced magnetisation m(H) to the saturation magnetisation m_{sat}: Δρ/ρ ≈ C(m/m_{sat})^{2}, where C ≈ x^{-2/3}, with x the number of charge carriers per magnetic unit cell. Comparison to data on very different ferromagnetic metals and doped semiconductors is in broad quantitative agreement with this trend, with the prime exception of the perovskite manganese oxides, already understood to involve the extra physics of dynamic lattice distortions. At very low doping, the physics should involve ferromagnetic polarons, and polaron formation and transport are discussed.
2
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Tunneling Conductivity of Manganites with Negative Magnetoresistance

100%
Medvedev Y., Tarenkov V., Svistunov V., Abaloshev A., Abalosheva I., Lewandowski S.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
827-830
EN
Tunneling investigations of ferromagnetic La_{0.6}Sr_{0.4}MnO_{3} ceramic samples showing negative magnetoresistance effect were carried out in two types of junctions: symmetric "break junctions" and asymmetric ceramics-insulator-metal junctions. The results are consistent with the presence of small ferromagnetic clusters in the insulating barriers of both types of junctions and suggest a two-phase state realized by impurity mechanism of phase separation.
3
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Multilayer Structures with Giant Magnetoresistance

63%
Stobiecki F., Stobiecki T.
Acta Physica Polonica A
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2002
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vol. 102
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issue 1
95-108
EN
The phenomenological description of the giant magnetoresistance effect as well as the discussion of the requirements which must be fulfilled in giant magnetoresistance thin film structures are given in the first part of our review. In the second part the magnetization reversal and giant magnetoresistance effect of antiferromagnetically coupled multilayers, spin valve and pseudo-spin valve thin film structures are explained. For these structures we also discuss the influence of the structure defects such as surface roughness and pinholes on the giant magnetoresistance effect.
4
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Magnetic and Electric Transport Properties of Fe-Hf-o Films Prepared by Supersonic Plasma Jet Method

63%
Soyka V., Kraus L., Frait Z., Šícha M., Jastrabík L.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
515-518
EN
The influence of deposition conditions on the structure, magnetic properties, and electrical resistivity of Fe-Hf-O films, prepared by the supersonic plasma jet deposition technique, was investigated. Composition of the films was controlled by the nozzle composition and the working gas. It varied in the limits: 15-68 at.% of Fe, 0.5-8 at.% of Hf and 29-80 at.% of O. The films were mainly X-ray amorphous. Some of them showed a weak and broad peak near the [110] reflection of α-Fe indicating the presence of Fe-rich clusters in an amorphous matrix. Depending on the deposition parameters the magnetic properties vary from paramagnetic to ferromagnetic ones. The electrical resistivity changes from the metallic to the hopping type. In some samples a large negative magnetoresistance is observed.
5
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Giant Magnetoresistance in Melt-Spun Co-Cu Modified by Rare Earths

63%
Idzikowski B., Rössler U., Handstein A., Nenkov K., Müller K.
Acta Physica Polonica A
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2000
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vol. 97
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issue 5
791-794
EN
Samples of the composition RE_{x}Co_{20}Cu_{80-x}, RE = Sm, Gd or Dy (x = 0, 1, and 3) were produced by melt-spinning and subsequent annealing. The magnetoresistance is negative as in granular Co-Cu, but its values depend on the kind of rare earth element added and on changes in the microstructure induced by thermal annealing. An addition of 1 at.% rare earth metal to Co_{20}Cu_{80} yields a considerable increase in the magnetoresistance ratio, whereas an addition of 3 at.% causes a decrease. E.g., by addition of 1 at.% Dy to Co_{20}Cu_{80} and optimal thermal treatment, the value of magnetoresistance ratio measured at 10 K in a field of 5 T increases from -14% to -28%. The effect can be attributed to the presence of clusters of hexagonal Dy(Co,Cu)_{5}, which was ascertained from X-ray diffraction data, or other, metastable rare-earth compounds and paramagnetic rare-earth atoms in the Cu matrix.
6
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The Spin-Valve Transistor - a New Magnetoelectronic Device

63%
Anil Kumar P., Lodder J.
Acta Physica Polonica A
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2000
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vol. 97
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issue 1
111-118
EN
A spin-valve transistor showing high sensitivity at low fields was developed. A large magnetocurrent, above 500% is realized by a magnetic field change of 2 to 4 Oe at 80 K. Hot electrons are injected into the spin-valve layer through a Si-Pt Schottky diode. These hot electrons, while traversing through the spin-valve, are spin-dependently scattered. Those electrons with right energy and momentum are collected by a collector (an Au-Si Schottky diode) constituting a collector current. The relative orientation of the magnetic layer in the spin-valve is changed by the application of a magnetic field and causes a change in collector current giving a large magnetocurrent.
7
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Influence of Temperature and Annealing on GMR in Sputtered Permalloy/Cu Multilayers

63%
Urbaniak M., Stobiecki F., Luciński T., Kopcewicz M., Grabias A., Aleksiejew J.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
539-542
EN
The influence of temperature and annealing on giant magnetoresistance of Si(100)/Cu(20 nm)/Py(2 nm)/(Cu(2 nm)/Py(2 nm))_{100} multilayer (Py = Ni_{83}Fe_{17}) sputtered at room temperature in double face-to-face configuration is reported. It was found that giant magnetoresistance value, ΔR_{GMR}/R_{sat} (where R_{sat} is the resistance in saturation), monotonically decreases with increasing temperature (4.5% at 173 K to about 1% at 373 K). This results from the decrease in magnetic change of resistance, ΔR_{GMR}, and to the lesser extent from an increase in R_{sat}, though both of them are caused by the shortening of electrons mean free path. The observed almost linear decrease in giant magnetoresistance saturation field with increasing temperature is explained by temperature changes of magnetization profile. Vibrating sample magnetometer measurements revealed that the increase in temperature results in pronounced decrease in remnant to saturation magnetization ratio (M_{r}/M_{s}) suggesting that at low temperatures magnetic bridges between Py layers play an important role in magnetization process. It is shown that proper annealing, by an annihilation of bridges and/or lateral decoupling, leads to an increase in giant magnetoresistance ratio from 3.4% in as deposited state to 4.7%.
8
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Current Fluctuations in Ferromagnetic Tunnel Junctions

51%
Bułka B., Martinek J., Michałek G., Barnaś J.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
423-426
EN
Current shot noise in a double junction consisting of a small metallic grain connected to two ferromagnetic electrodes is analysed in the limit of sequential tunneling. We show that, apart from charge fluctuations, there are strong spin fluctuations. We also show that two distinct relaxation processes can be distinguished in the frequency dependent current noise: one in a low frequency range and corresponding to spin fluctuations and another one in a high frequency range corresponding to charge fluctuations.
9
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Content available

Electrical Transport and Magnetic Properties of La_{2/3}Pb_{1/3}MnO_3 Thin Films

51%
Baran M., Berkowski M., Fink-Finowicki J., Lewandowski S., Szymczak H., Szymczak R., Khartchev S., Medvedev Y.
Acta Physica Polonica A
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2004
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vol. 105
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issue 1-2
115-120
EN
The magnetic and transport properties of epitaxial La_{2/3}Pb_{1/3}CuO_3 thin films deposited on SrLaGaO_4 substrate using dc magnetron sputtering technique are reported. The giant magnetoresistance effect (of about 50% at magnetic field of 1 T) was observed near the Curie temperature. Several mechanisms responsible for temperature dependence of resistivity are discussed. The effect of annealing was studied. It shifted the Curie temperature to the lower value, probably, because of the loss of oxygen.
10
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Magnetism and Magnetoresistance of Multilayers Prepared on Microstructured Substrates

51%
Shinjo T., Ono T., Shigeto K., Sugita Y.
Acta Physica Polonica A
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1997
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vol. 91
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issue 1
27-36
EN
Magnetic multilayers with a new type of structural modification were prepared by ultrahigh vacuum deposition onto substrates with V-shaped microgrooves and used as the samples for the following two novel studies: One is the study of giant magnetoresistance in a new geometry, CAP, where the electric current is at a certain angle to interfaces. Enhancement of magnetoresistance in CAP geometry, in comparison to the normal current in-plane magnetoresistance, was confirmed. The other is the study of magnetic thin wires, which were prepared by depositing in a tilted direction to the surface. A preliminary result of magnetization reversal investigation is presented.
11
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Content available

Synthesis and Electrical Properties of La-Pr-Mn-O Thin Films and Heterostructures

51%
Butkutė R., Anisimovas F., Oginskis A., Steikūnienė A., Devenson J., Vengalis B.
Acta Physica Polonica A
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2007
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vol. 111
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issue 1
111-115
EN
In this paper we report the results of synthesis and study of both ceramic samples and thin films of electronically doped La_{0.7}Pr_{0.3}MnO_3 and related heterostructures composed of La_{0.7}Pr_{0.3}MnO_3 and p-type La_{0.67}Ca_{0.33}MnO_3. The ceramic La_{0.7}Pr_{0.3}MnO_3 samples were prepared by a conventional solid state reaction technique. Single phase La_{0.7}Pr_{0.3}MnO_3 thin films and La_{0.7}Pr_{0.3}MnO_3/La_{0.67} Ca_{0.33}MnO_3 heterostructures were grown on lattice-matched perovskite NdGaO_3 substrates by pulsed laser deposition. Electron doping was indicated both for ceramic La_{0.7}Pr_{0.3}MnO_3 samples and thin films from thermopower data. Both ceramic samples and thin films of La_{0.7}Pr_{0.3}MnO_3 demonstrated resistivity of about 10 mΩ cm at 300 K and semiconductor-like resistance vs. temperature behavior with cooling down to 78 K. Meanwhile, the resistance of the La_{0.7}Pr_{0.3}MnO_3/La_{0.67}Ca_{0.33}MnO_3 interface showed an anomalous peak at 185 K. A series of post-deposition annealing experiments demonstrated a crucial role of annealing temperature and ambience on both electrical and magnetic properties of La_{0.7}Pr_{0.3}MnO_3 material and the heterostructures.
12
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Composition and Temperature Dependence of Giant Magnetoresistance in Melt-Spun Co_{x}Cu_{100-x} Ribbons

51%
Idzikowski B., Nenkov K., Handstein A., Hütten A., Müller K.-H.
Acta Physica Polonica A
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1997
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vol. 92
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issue 2
307-310
EN
Structure, magnetic properties and magnetoresistance in as-quenched and annealed Co_{x}Cu_{100-x} samples were investigated. Homogeneous metastable Co_{x}Cu_{100-x} alloys were prepared by the single-roller technique. The maximum value of magnetoresistance is shifted to higher annealing temperatures with increasing measuring temperature. At higher measuring temperatures the magnetoresistance is not saturated in fields as high as 16 T. Susceptibility measurements showed the formation of hcp-structured Co clusters. For small cobalt concentrations there is a transition from giant magnetoresistance to the normal anisotropic magnetoresistance.
13
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Scattering Theory of the Johnson Spin Transistor

51%
Geux L., Brataas A., Bauer G.
Acta Physica Polonica A
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2000
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vol. 97
|
issue 1
119-128
EN
We discuss a simple, semiclassical scattering theory for spin-dependent transport in a many-terminal formulation, with special attention to the four terminal device of Johnson referred to as spin transistor.
14
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Temperature Dependence of Magnetisation Reversal and GMR in Spin Valve Structures

51%
Stobiecki F., Stobiecki T., Ocker B., Maass W., Powroznik W., Paja A., Loch C., Röll K.
Acta Physica Polonica A
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2000
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vol. 97
|
issue 3
523-526
EN
Temperature measurements of magnetisation reversal, resistance and magnetoresistance of Co/Cu/Co/FeMn spin valve structures deposited in different conditions were performed. The influence of exchange anisotropy energy, interlayer coupling energy, and electron transport properties were taken into consideration in explaining differences in giant magnetoresistance effect of investigated samples.
15
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Structural Studies of Co/Cu and Co/Ru Interfaces Using ^{59}Co NMR Method

51%
Wójcik M., Jędryka E., Nadolski S., Kubinski D., Parsons M., Holloway H.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
551-554
EN
The structural and magnetic properties of three magnetron sputtered multilayers at the 2nd maximum of antiferromagnetic coupling were studied using ^{59}Co NMR spectroscopy: [Co(20 Å)/Cu(20 Å)]_{20}, [Co(20 Å )/ Ru(18 Å)]_{20} and a heterostructure, in which non-magnetic spacers alternated between Cu and Ru. Co/Cu interfaces were found to be relatively sharp, extended over 3 monolayers, while the Co/Ru interfaces extend over 6 monolayers due to the good miscibility of Co and Ru. The NMR restoring field in the heterostructure is found to be the average of the restoring fields in both reference samples.
16
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Magnetic Properties and GMR of Sputtered Permalloy/Au Multilayers

51%
Szymański B., Stobiecki F.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
535-538
EN
We report on structural, magnetic, and GMR properties of permalloy/Au multilayers where permalloy = Ni_{83}Fe_{17}, deposited by face-to-face sputtering onto Si(111) substrate. X-ray diffraction studies confirmed a good structural quality of our multilayers. The samples were characterised with vibrating sample magnetometer, longitudinal magnetooptical Kerr effect and giant magnetoresistance measurements. It was determined that our multilayers are magnetically very soft with H_{c} ≈ 1 Oe and show uniaxial anisotropy with H_{K} ≈ 5 Oe. For gold sublayer thickness d_{Au} close to 1.1 nm the antiferromagnetic coupling is present in very narrow Au thickness range (≈ 0.2 nm). Despite a good structural quality of samples relatively small giant magnetoresistance value (1.2% at room temperature) was found. It is due to non-perfect aniferromagnetic coupling caused by pinholes.
17
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Conductance of Mesoscopic Magnetic Systems

51%
Krompiewski S.
Acta Physica Polonica A
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2000
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vol. 97
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issue 1
15-24
EN
Theoretical studies of electrical conductance of various nanowires are performed within the framework of a semi-realistic s-d tight-binding model. The presented results concern both homogeneous paramagnetic and ferromagnetic systems as well as trilayers composed of 2 magnetic slabs separated by a nonmagnetic spacer. On the one hand, in the case of the homogeneous systems the attention is focused on conductance quantization, which manifests itself when a contact gets open and conduction decays in a spectacular stepwise way. A new approach is developed by assuming that in the last stage of the breaking of the contact between wires there are fewer and fewer, distributed at random, conduction paths passing through the nanowire cross-section. The corresponding conductances are calculated within the quasiballistic regime, using the Kubo formula and a recursion Green function technique. The results for weak ferromagnets (when both majority and minority bands intersect the Fermi surface) are qualitatively different from those for strong ferromagnets (only the minority bands do), which may explain experimental cumulative conductance histograms of Fe and Ni. On the other hand, giant magnetoresistances of magnetic trilayers are studied for both current-perpendicular-to-plane and current-in-plane geometries. The corresponding magnetoresistances are compared with each other and with the interlayer exchange coupling.
18
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Transport Properties of the U_{1-x}Th_{x}Pt System

51%
Tran V., Troć R.
Acta Physica Polonica A
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2000
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vol. 97
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issue 3
399-402
EN
We present the results of measurements of electrical resistivity (ρ(T)) and magnetoresistance (Δϱ/ϱ_{0}(T)) on the solid solutions U_{1-x}Th_{x}Pt (x=0-0.8). The Curie temperature (T_{c}=21 K) found for the parent compound UPt, is steadily reduced upon the Th-substitution. The ρ(T) and Δϱ/ϱ_{0}(T) functions provide evidence of electron scattering due to spin fluctuations. The most interesting feature of Δϱ/ϱ_{0} is its high value of about -22% found for UPt and U_{0.9}Th_{0.1}Pt at their T_{c} and B=8 T. For samples with x ≥ 0.2, the value of Δϱ/ϱ_{0} at 4 K and 8 T increases with x and becomes positive for Th-composition x >= 0.6.
19
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CPP-Giant Magnetoresistance and Thermoelectric Power of Multilayers

51%
Krompiewski S., Krey U.
|
EN
Oscillations of magnetoresistance and thermoelectric power vs. both nonmagnetic spacer and ferromagnetic slab thicknesses are studied in the current-perpendicular-to-plane geometry, in terms of the single-band tight-binding model. The spin-dependent conductance was calculated from the Kubo formula by means of a recursion Green function technique, and the thermoelectric power directly from the well-known Onsager relations. In general, the observed oscillations may have either just one or two periods. In the latter case the long period of oscillations, related to spectacular beats, is apparently of non-RKKY type. The relative thermoelectric power oscillations are strongly enhanced in comparison with those of the giant magnetoresistance, have the same periods, but different phases and a negative bias.
20
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Spin-Dependent Phenomena in Magnetoelectronic Devices

51%
BarnaŚ J., Gmitra M., Rudziński W., Wawrzyniak M., Dugaev V., Kunert H.
Acta Physica Polonica A
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2007
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vol. 112
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issue 6
1259-1265
EN
Spin effects in electronic transport properties of artificial magnetic structures, like nanopillar spin valves, tunnel junctions, mesoscopic double-barrier junctions (single-electron transistors) are briefly discussed. Two classes of spin effects are distinguished; i.e. magnetoresistance phenomena due to magnetization rotation, and current-induced magnetic switching and magnetic dynamics.
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