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1
Content available remote

Diffuse Neutron Scattering in the Mn_{0.4}Cu_{0.6} Alloy

100%
Jankowska-Kisielińska J., Mikke K., Fijał-Kirejczyk I.
Acta Physica Polonica A
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2008
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vol. 113
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issue 4
1171-1178
EN
The diffuse neutron scattering in the Mn_{0.4}Cu_{0.6} alloy was measured in the temperature range 15-390K at the 3-axis neutron spectrometer at MARIA reactor in Świerk. The broad maxima of the neutron intensity were observed in the surrounding of the (0.5, 1, 0) reciprocal lattice point and other symmetry related points. The effect is similar to that observed in Mn-Cu alloys with lower Mn content at room temperature. Our results are in agreement with the earlier finding that the maxima of the short-range order incommensurate spin density wave scattering are placed at the (0.5±δ, 1, 0) reciprocal lattice point with a linear dependence of δ on the Mn concentration. In addition, some commensurate antiferromagnetic short-range order was found.
2
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Influence of Quadrupole Interaction on ^{57}Fe Mössbauer Spectra for Samples with Charge- and Spin-Density Waves

100%
Cieślak J., Dubiel S. M.
Acta Physica Polonica A
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1997
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vol. 91
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issue 6
1131-1139
EN
The influence of the quadrupole interaction on the shape of ^{57}Fe Mössbauer spectra expected for samples with charge-density waves andor spindensity waves is investigated. It is shown, by model calculations, that both for the commensurate and for incommensurate charge-density waves andor spin-density waves the shape of ^{57}Fe Mössbauer spectra is sensitive to the value, and for asymmetric spectra, to the sign of quadrupole interaction. This necessitates an inclusion of quadrupole interaction when analyzing the spectra recorded on samples exhibiting charge-density waves andor spin-density waves, and having a symmetry lower than cubic.
3
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Application of the ^{119}Sn Mössbauer-Effect Spectroscopy in the Investigation of Spin-Density-Waves in Chromium

100%
Dubiel S.
Acta Physica Polonica A
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1993
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vol. 84
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issue 1
83-100
EN
Application of ^{119}Sn Mossbauer-effect spectroscopy in an investigation of spin-density-waves in chromium in terms of model calculations as well as of measurements on real samples is presented.
4
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Inelastic Neutron Scattering in Sendust Alloy in 8-295 K Temperature Range

100%
Świderska K., Jankowska-Kisielińska J., Dobrzyński L.
Acta Physica Polonica A
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2012
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vol. 122
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issue 2
400-404
EN
The effects concerning magnetic and nuclear excitations in a single crystal of Sendust alloy (73.5 at.% Fe, 9.5 at.% Al, 17 at.% Si) are discussed. The excitations have been investigated by means of elastic and inelastic neutron scattering with the use of triple axis and small angle spectrometer. A few potential causes of spin wave damping in Sendust, like interactions of excitations or small-size precipitations of different compositions or directions of magnetization were disproved. It is suggested that one- and two-phonon scattering can explain observed strong increase of incoherent inelastic scattering with temperature.
5
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On a Field-Induced Spin-Density Wave in Bechgaard Salts

100%
Apostol M.
Acta Physica Polonica A
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1994
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vol. 85
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issue 6
971-978
EN
A new type of field-induced spin-density wave is shown to occur in a weak-coupling layered model which may be relevant for the highly anisotropic electronic structure of the Bechgaard salts. The modulation vector of this instability is perpendicular to the layers and close to the direction of the magnetic field applied perpendicular to the reciprocal layers. The magnitude of the modulation vector, order parameter and critical temperature have an oscillatory dependence on the magnitude of the magnetic field.
6
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Interplay Between Spin Density Wave and Superconductivity in `122' Iron Pnictides: ^{57}Fe Mössbauer Study

100%
Błachowski A., Ruebenbauer K., Żukrowski J., Bukowski Z., Matusiak M., Karpinski J.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
726-729
EN
Iron-based superconductors Ba_{0.7}Rb_{0.3}Fe_{2}As_{2} and CaFe_{1.92}Co_{0.08}As_{2} of the `122' family have been investigated by means of the 14.41-keV Mössbauer transition in ^{57}Fe versus temperature ranging from the room temperature till 4.2 K. A comparison is made with the previously investigated parent compounds BaFe_{2}As_{2} and CaFe_{2}As_{2}. It has been found that Mössbauer spectra of these superconductors are composed of the magnetically split component due to development of spin density wave and non-magnetic component surviving even at lowest temperatures. The latter component is responsible for superconductivity. Hence, the superconductivity occurs in the part of the sample despite the sample is single phase. This phenomenon is caused by the slight variation of the dopant concentration across the sample (crystal).
7
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Magnetic and Electronic Properties of Selected Rare-Earth Chromium Germanides Compounds

100%
Gil A., Makowska-Janusik M.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
385-387
EN
The ternary rare-earth compounds exhibit interesting physical and structural properties. These structures changing composition and stoichiometry change drastically their magnetic properties. Some of them, based on chromium germanides were studied experimentally concerning their magnetic properties and up to our knowledge they were never studied theoretically explaining nature of their magnetic behaviour. In the presented work the nature and mechanism of the magnetic and electronic properties of rare-earth chromium germanides is presented. The magnetic and electronic properties of RCrGe₂ and RCr_{0.3}Ge₂ (R = Tb, Dy, Ho or Er) were investigated theoretically applying plane-wave density functional theory/Perdew-Burke-Ernzerhof methodology. The computational investigations were performed for the stoichiometric and nonstoichiometric crystal structure with the space group Cmcm. The stoichiometry of the rare-earth chromium germanides compounds has significant effect on the magnetic properties of the investigated material. The theoretical predictions are compared to the experimentally obtained results.
8
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Structure and Short Range Order of Two Phases in the Single Domain Mn_{0.75}Cu_{0.25} Alloy after Spinodal Decomposition

100%
Jankowska-Kisielińska J., Świderska K., Mikke K.
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issue 4
582-585
EN
The aim of the present paper was to identify the atomic and magnetic structure and short-range order of the two phases present in the Mn_{0.75}Cu_{0.25} alloy after decomposition and plastic deformation. The sample was investigated by elastic neutron scattering at small-angle and 3-axes spectrometers. We have confirmed the decomposition of the alloy into two types of regions with manganese concentration increased and decreased as compared with the mean value. The crystal lattice in regions of both types is tetragonal (pseudo FCT) below T_{N} but degree of tetragonal distortion is different. The long range antiferromagnetic order is present only in the regions of bigger distortion and higher Mn concentration. In the regions of lower Mn content and smaller distortion there is a short range ordering of complex magnetic and atomic character.
9
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Kondo Screening Effect and Ferromagnetic Order in UCu_2Si_2

100%
Troć R., Samsel-Czekała M., Coqblin B.
Acta Physica Polonica A
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2012
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vol. 121
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issue 5-6
1023-1025
EN
Electrical resistivity and low temperature magnetoresistivity measurements made on a single crystal of UCu_2Si_2 are reported. By using as a phonon reference the temperature dependence of the electrical resistivity of ThCu_2Si_2 we could establish that UCu_2Si_2 has both a ferromagnetic and a Kondo behaviour. Such a phenomenon can be described by the underscreened Kondo lattice model. The magnetoresistivity revealed the presence of magnetic fluctuations within the ferromagnetic order as it was reported previously for UGe_2. Also one of the calculated Fermi surface sheets exhibits nesting properties, being in perfect agreement with the previous neutron diffraction data, supporting the possibility of a presence of the spin density wave phase. In this ternary silicide, where the strong ferromagnetic behaviour exists, this phase is signalised by magnetic fluctuations.
10
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Superconductivity and Quantum Critical Behavior in Cr_{100-z}Os_z

100%
Prinsloo A., Sheppard C., Fernando P.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1132-1134
EN
The magnetic phase diagrams of Cr alloys with group-8 metals, such as Re and Ru, show interesting properties. These include quantum critical and superconducting behavior. In order to extend these investigations this paper reports on the physical properties and the magnetic phase diagram of the Cr_{100-z}Os_{z} system, investigated in a concentration range of 2 ≤ z ≤ 30.6. Structural analysis indicate that samples with z<22 have a bcc structure, while those with z>22 include a cubic A15-type structure. Transport and magnetic property measurements indicate that the antiferromagnetic phase disappears at z ≈ 14 and that samples with concentrations z ≥ 12.2 show superconducting behavior. The magnetic phase diagram of Cr_{100-z}Os_{z} is constructed from the Néel and superconducting transition temperatures obtained from various measurements. The commensurate spin-density-wave to paramagnetic phase line decreases sharply for z>4. Fitting parameters of a power law fit to the commensurate spin-density-wave to paramagnetic phase line indicate possible quantum critical behavior. Present results suggest that this phase line terminates in a superconducting dome near a magnetic quantum critical point, similar to that observed in certain heavy fermion systems, but not previously reported for other Cr alloys.
11
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On the Phase Diagram of the Zero-Bandwidth Extended Hubbard Model with Intersite Magnetic Interactions for Strong On-Site Repulsion Limit

100%
Murawski S., Kapcia K., Pawłowski G., Robaszkiewicz S.
Acta Physica Polonica A
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2012
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vol. 121
|
issue 5-6
1035-1037
EN
In this report we have analyzed a simple effective model for a description of magnetically ordered insulators. The Hamiltonian considered consists of the effective on-site interaction (U) and the intersite Ising-like magnetic exchange interaction (J) between nearest neighbors. For the first time the phase diagrams of this model have been determined within Monte Carlo simulation on 2D-square lattice. They have been compared with results obtained within variational approach, which treats the on-site term exactly and the intersite interactions within mean-field approximation. We show within both approaches that, depending on the values of interaction parameters and the electron concentration, the system can exhibit not only homogeneous phases: (anti-)ferromagnetic (F) and nonordered (NO), but also phase separated states (PS: F-NO).
12
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On Effect of Spin-Density Wave Parameters on Shape of ^{119}Sn Mössbauer Spectra

100%
Cieślak J., Dubiel S. M.
Acta Physica Polonica A
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1995
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vol. 88
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issue 6
1143-1150
EN
Based on a simple numerical procedure the influence of various para­meters characteristic of spin-density waves on the shape of ^{119}Sn Mössbauer spectra and the related histograms of the Hyperfine field distributions is investigated.
13
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Residual Stress in Cr₉₉Al₁ Polycrystalline Thin Films

100%
Mudau Z., Sheppard C., Prinsloo A., Venter A., Ntsoane T., Fullerton E.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
578-581
EN
The magnetic phase diagram of bulk Cr_{100-x}Al_{x} shows interesting behaviour close to the triple point concentration of x ≈2. Since the magnetic properties of Cr are influenced by dimensionality, stress and strain, this study focussed on the investigation of Cr₉₉Al₁ thin films prepared on fused silica substrates with thicknesses t varying from 29 to 452 nm using sputtering techniques. Resistance measurements covering the temperature range 2 to 400 K did not show any clear anomalies that could be indicative of changes in the magnetic ordering. X-ray diffraction (XRD) and atomic force microscopy (AFM) studies indicate the films are polycrystalline textured and that the 80 nm sample has the smallest grain size. In-plane stresses in these thin films were studied using the specialised XRD ın²ψ-method. The results show that the stress varies with film thickness. The 29 nm sample has stress in the order of 833 MPa and with increasing film thickness the stress reaches 1471 MPa for the 80 nm layer, where after it systematically reduces for the thicker coatings to 925 MPa for the 452 nm film. The highest stress for the Cr₉₉Al₁ thickness sample series is seen in the film with the smallest grain size.
14
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Some Properties of Two-Dimensional Extended Repulsive Hubbard Model with Intersite Magnetic Interactions - A Monte Carlo Study

88%
Murawski S., Kapcia K., Pawłowski G., Robaszkiewicz S.
|
|
vol. 126
|
issue 4a
A-110-A-114
EN
In this paper the two-dimensional extended Hubbard model with intersite magnetic Ising-like interaction in the atomic limit is analyzed by means of the classical Monte Carlo method in the grand canonical ensemble. Such an effective simple model could describe behavior of insulating (anti)ferromagnets. In the model considered the Coulomb interaction (U) is on-site and the magnetic interactions in z-direction (J>0, antiferromagnetic) are restricted to nearest-neighbors. Simulations of the model have been performed on a square lattice consisting of N=L× L=400 sites (L=20) in order to obtain the full phase diagram for U/(4J)=1. Results obtained for on-site repulsion (U>0) show that, apart from homogeneous non-ordered (NO) and ordered magnetic (antiferromagnetic, AF) phases, there is also a region of phase separation (PS: AF/NO) occurrence. We present a phase diagram as well as some thermodynamic properties of the model for the case of U/(4J)=1 (and arbitrary chemical potential and arbitrary electron concentration). The AF-NO transition can be second-order as well as first-order and the tricritical point occurs on the diagram.
15
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Some Properties of the Model of a~Superconductor with Pair Hopping and Magnetic Interactions at Half-Filling

88%
Kapcia K.
Acta Physica Polonica A
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2012
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vol. 121
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issue 4
733-737
EN
We present our preliminary studies of an effective model of a superconductor with short coherence length involving magnetic interactions. The Hamiltonian considered consists of (i) the effective on-site interaction U, (ii) the intersite magnetic exchange interactions (J^z, J^{xy}) between nearest-neighbors and (iii) the intersite charge exchange term I, determining the hopping of electron pairs between nearest-neighbor sites. In the analysis of the phase diagrams and thermodynamic properties of this model for half-filling (n=1) we have adopted the variational approach, which treats the on-site interaction term exactly and the intersite interactions within the mean-field approximation. One finds that the system considered can exhibit very interesting multicritical behaviors (including tricritical, critical-end and bicritical points) caused by the competition between magnetism and superconductivity, even for n=1. Our investigations show that, depending on the values of interaction parameters, the system at half-filling can exhibit three homogeneous phases: superconducting (SS), (anti-)ferromagnetic (F) and nonordered (NO). The transitions between ordered phases (SS, F) and the NO phase can be first order as well as second order ones, whereas SS-F transition is first order one. Temperature dependencies of the order parameters and thermodynamic properties of the system at the sequence of transitions: SS→F→NO with increasing temperature for J/I=0.3, U/I_0 = 0.69 and n=1 are also presented.
16
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Magnetic Topological Structures in Multiferroics

88%
Gareeva Z., Zvezdin K., Popkov A., Zvezdin A.
Acta Physica Polonica A
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2018
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vol. 133
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issue 3
380-383
EN
In this article we focus on impact of micromagnetic structures on magnetoelectricity of multiferroics. We discuss physical mechanisms of magnetoelectric coupling considering domain walls and spin cycloids. We review the progress on multiferroic materials focusing on high temperature multiferroic: rare earth iron garnet and bismuth ferrite. We argue that topological structures play a pivotal role in multiferoics and show that electric control of magnetism can be carried out via spin spirals and domain walls. Magnetic domain walls produce ferroelectricity in rare earth iron garnets; transformations of spin cycloids release magnetoelectricity in bismuth ferrite. Ferroic orders couple via magnetic inhomogeneities, which shed new light on fundamental physics and applications.
17
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Interplay between Charge and Magnetic Orderings in the Zero-Bandwidth Limit of the Extended Hubbard Model for Strong On-Site Repulsion

88%
Kapcia K., Kłobus W., Robaszkiewicz S.
Acta Physica Polonica A
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2012
|
vol. 121
|
issue 5-6
1032-1034
EN
A simple effective model of charge ordered and (or) magnetically ordered insulators is studied. The tight binding Hamiltonian analyzed consists of (i) the effective on-site interaction U, (ii) the intersite density-density interaction W and (iii) intersite magnetic exchange interaction J^{z} (or J^{xy}) between nearest-neighbors. The intersite interaction are treated within the mean-field approximation. One shows that the systems considered can exhibit very interesting multicritical behaviors, including among others bicritical, tricritical, tetracritical and critical end points. The analysis of the model has been performed for an arbitrary electron concentration as well as an arbitrary chemical potential in the limit of strong on-site repulsion (U → +∞). The phase diagrams obtained in such a case are shown to consist of at least 9 different states, including four homogeneous phases: nonordered (NO), ferromagnetic (F), charge ordered (CO), ferrimagnetic (intermediate, I) and five types of phase separation: NO-NO, F-NO, F-F, CO-F, CO-I.
18
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Some Exact Results for the Zero-Bandwidth Extended Hubbard Model with Intersite Charge and Magnetic Interactions

88%
Kapcia K., Kłobus W., Robaszkiewicz S.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
284-286
EN
The extended Hubbard model in the zero-bandwidth limit is studied. The effective Hamiltonian consists of (i) on-site U interaction, (ii) intersite density-density interaction W, and (iii) Ising-like magnetic exchange interaction J between the nearest-neighbors. We present rigorous (and analytical) results obtained within the transfer-matrix method for 1D chain in two particular cases: (a) W=0 and n=1; (b) U → +∞ and n=1/2 (W ≠ 0, J ≠ 0). We obtain the exact formulae for the partition functions which enables to calculate thermodynamic properties such as entropy, specific heat (c), and double occupancy per site. In both cases the system exhibits an interesting temperature dependence of c involving a characteristic two-peak structure. There are no phase transitions at finite temperatures and the only transitions occur in the ground state.
19
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Monte Carlo Study of Phase Separation in Magnetic Insulators

88%
Murawski S., Kapcia K., Pawłowski G., Robaszkiewicz S.
Acta Physica Polonica A
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2015
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vol. 127
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issue 2
281-283
EN
In this work we focus on the study of phase separation in the zero-bandwidth extended Hubbard with nearest-neighbors intersite Ising-like magnetic interactions J and on-site Coulomb interactions U. The system has been analyzed by means of the Monte Carlo simulations (in the grand canonical ensemble) on two-dimensional square lattice (with N = L × L = 400 sites) and the results for U/(4J) = 2 as a function of chemical potential and electron concentration have been obtained. Depending on the values of interaction parameters the system exhibits homogeneous (anti-)ferromagnetic or non-ordered phase as well as phase separation state. Transitions between homogeneous phases (i.e. antiferromagnetic-non-ordered transitions) can be of first or second order and the tricritical point is also present on the phase diagrams. The electron compressibility K is an indicator of the phase separation and that quantity is of particular interest of this paper.
20
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Angular Magnetoresistance of a Possible Kondo Insulator CeOs₄Sb₁₂ Measured at Ultra-Low Temperatures

75%
Bochenek Ł., Cichorek T.
Acta Physica Polonica A
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2016
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vol. 130
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issue 2
600-603
EN
Angular magnetoresistance of the filled skutterudite compound CeOs₄Sb₁₂ has been investigated along the [110] direction. Distinct differences between the angular magnetoresistance data at T = 0.55 K and 4.2 K coincide with a developing of spin-density waves at T ≈ 1.7 K in B = 5 T. Magnetoresistance experiments have been performed on a self-made assembly utilizing a commercial piezoelectric rotator.
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