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    Wyświetlanie 1-8 z 8
    Tytuł:
    Observation of Magnetic Anisotropy in GaN:Cr Single Crystals
    Autorzy:
    Gosk, J.
    Boćkowski, M.
    Kowalski, G.
    Grzegory, I.
    Szczytko, J.
    Twardowski, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1403624.pdf
    Data publikacji:
    2012-12
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.55.Eq
    75.30.Gw
    75.50.Pp
    75.10.Dg
    Opis:
    Magnetic properties of bulk wurtzite GaN:Cr single crystals were studied with the magnetic field applied parallel and perpendicular to the crystal wurtzite c-axis. Structure of the crystal was examined by the X-ray diffraction method. Strong anisotropy of magnetization at low temperatures (2-10 K) was observed. The experimental data suggest Cr to be in nonspherical $d^4$ configuration.
    Źródło:
    Acta Physica Polonica A; 2012, 122, 6; 1007-1009
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Magnetization of GaMnN Ceramics Prepared from Nanopowders by an Anaerobic Synthesis and High-Pressure High-Temperature Sintering
    Autorzy:
    Gosk, J.
    Drygaś, M.
    Janik, J.
    Gierlotka, S.
    Pałosz, B.
    Twardowski, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1398535.pdf
    Data publikacji:
    2016-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.50.Mm
    81.07.Wx
    81.07.-b
    Opis:
    Herein, we report a study on magnetic properties of GaMnN ceramics prepared by no additive high-pressure high-temperature sintering of a range of nanopowders, the latter made via an anaerobic synthesis method in the Ga/Mn bimetallic system at various nitridation temperatures and different levels of initial Mn concentration. Measurements of the magnetization as a function of temperature and magnetic field for the ceramics and parent nanopowders showed a typical paramagnetic behavior. Antiferromagnetic interactions between Mn-ions incorporated in the GaN lattice, GaMnN, were revealed and shown to be much stronger in the ceramics than in the respective nanopowders. In addition, in all of these materials an antiferromagnetic contribution originating from a residual Mn₂SiO₄ by-product was also observed. The highest calculated Mn concentration in the nanopowders reached 3.4 at.%. Complex mixtures of gallium nitride polytypes with multimodal particle size distributions in the nanosized range (small nano: 2-8 nm, large nano: 35-60 nm) were converted upon sintering to the single hexagonal GaN phase with average crystallite sizes of 40-80 nm and higher. For the optimal 700°C-treated materials, the Mn concentration in the parent GaMnN nanopowder was 3.2 at.% whereas in the derived ceramics it amounted to 5.5 at.%. At the same time, contributions of the adventitious Mn₂SiO₄ by-product significantly decreased upon sintering.
    Źródło:
    Acta Physica Polonica A; 2016, 129, 1a; A-103-A-106
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Superconductivity Study of GaN Highly Doped by Transition Metals
    Autorzy:
    Gosk, J.
    Boćkowski, M.
    Tokarczyk, M.
    Kowalski, G.
    Twardowski, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/1399142.pdf
    Data publikacji:
    2013-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    74.25.Ha
    74.70.-b
    74.25.Dw
    75.50.-y
    61.72.Dd
    81.10.Dn
    Opis:
    GaN:Cr and GaN:Fe single crystals as well as GaN:Mn micropowders highly doped by transition metals were grown to investigate low temperature superconductivity. Magnetic measurements revealed type I superconductivity with $T_{C} ≈ 6 K$ and $H_{C} ≈ 600 Oe$, identical for all compounds and also identical to that observed before in GaP:Cr and GaAs:Cr. The presence of amorphous inclusions of gallium may explain existing superconductivity as a result of a phase transition leading to β-Ga during cooling down of the sample. Since the observed parameters are close to those characteristic for superconducting Ga(II) this possibility could not be ruled out.
    Źródło:
    Acta Physica Polonica A; 2013, 124, 5; 877-880
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Effect of the sign of anisotropy constants on the properties of the system of interacting ferromagnetic nanoparticles
    Autorzy:
    Sadek, M.
    Marchwiany, M.
    Woinska, M.
    Majhofer, A.
    Gosk, J.
    Twardowski, A.
    Szczytko, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1159850.pdf
    Data publikacji:
    2016-01
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.40.Mg
    75.50.Tt
    75.75.-c
    Opis:
    We use the Monte Carlo simulation method to investigate the influence of the signs of magnetocrystalline anisotropy constants and the magnetic dipole-dipole interactions on the zero field cooled-field cooled magnetization experiments and hysteresis curves of a system of magnetic nanoparticles. Positive first cubic anisotropy constant K₁ results in larger blocking temperatures and larger coercive fields of a system, while the second anisotropy constant K₂ is practically of negligible importance for the phenomena investigated. Magnetic dipole-dipole interactions are important only in the most dense systems of particles and their effects practically disappear for systems where the distance between the closest particles exceeds three particle diameters.
    Źródło:
    Acta Physica Polonica A; 2016, 129, 1a; A-53-A-55
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    EPR Spectra of Multispin Systems. Application to Poly-m-p-Aniline
    Autorzy:
    Juszyński, P.
    Twardowski, A.
    Gosk, J.
    Kulszewicz-Bajer, I.
    Pawłowski, M.
    Dziatkowski, K.
    Szczytko, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/2048138.pdf
    Data publikacji:
    2011-05
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    02.70.-c
    75.10.-b
    Opis:
    In this communication we present NiceMagnetic, software for simulations and analysis of EPR spectrum and SQUID measurements. Systems of arbitrary number N of spin-only magnetic moments (S ≤ 0 and L = 0) were considered within the lines of the Heisenberg and Zeeman Hamiltonians. Effective algorithms used for the computations are discussed. This includes modified secant method adapted to calculate resonance fields with demanded precision. Finally, application of NiceMagnetic to experimental SQUID magnetization and EPR spectra of poly-m-p-aniline, one of recently synthesized high spin polymers containing unpaired electrons will be presented. As a result, exchange integral between electron and nitrogen nuclei spins (ligand hyperfine interaction) J = 6.3 × 10$\text{}^{-4}$ cm$\text{}^{-1}$ was estimated.
    Źródło:
    Acta Physica Polonica A; 2011, 119, 5; 717-719
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Observation of Magnetic Anisotropy in Bulk GaMnN:Mg Crystals
    Autorzy:
    Gosk, J.
    Zając, M.
    Kamińska, M.
    Twardowski, A.
    Grzegory, I.
    Boćkowski, M.
    Porowski, S.
    Powiązania:
    https://bibliotekanauki.pl/articles/2036861.pdf
    Data publikacji:
    2003-06
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.55.Eq
    75.30.Gw
    75.50.Pp
    Opis:
    Magnetic properties of bulk wurtzite n-type GaMnN and highly resistive GaMnN:Mg monocrystals were studied for the magnetic field applied parallel and perpendicular to the crystal hexagonal c-axis. Magnetization of both types of samples reveals paramagnetic behavior. However, for n-type GaMnN isotropic magnetization was observed which is in agreement with Mn d$\text{}^{5}$ configuration. On the other hand, GaMnN co-doped with Mg shows large magnetic anisotropy which suggests Mn to be in nonspherical d$\text{}^{4}$ or d$\text{}^{3}$ configuration.
    Źródło:
    Acta Physica Polonica A; 2003, 103, 6; 665-669
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Magnetic Properties of Epitaxial Fe/(Ga,Mn)As Hybrids
    Autorzy:
    Kalbarczyk, K.
    Dziatkowski, K.
    Szczytko, J.
    Gosk, J.
    Tokarczyk, M.
    Kowalski, G.
    Twardowski, A.
    Bednarski, W.
    Ostrowski, A.
    Waplak, S.
    Martinek, J.
    Liu, X.
    Furdyna, J.
    Powiązania:
    https://bibliotekanauki.pl/articles/1399140.pdf
    Data publikacji:
    2013-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    75.75.-c
    75.30.Gw
    75.50.Pp
    75.50.Bb
    Opis:
    Thin-film structures composed of two kinds of ferromagnetic material - metallic Fe and semiconducting (Ga,Mn)As - were investigated by means of SQUID magnetometry and ferromagnetic resonance spectroscopy. Dependence of remnant magnetic moment on temperature showed unexpected anisotropic features when recorded along two orthogonal in-plane directions. For one of these orientations, the change in sign of the slope of m(T) curve at the Curie point of (Ga,Mn)As was observed, while for the other, an analogous m(T) curve retained monotonic character. Based on the comparison with ferromagnetic resonance data, the apparent non-monotonicity was attributed to the temperature-induced change of balance between the external magnetic field and uniaxial magnetic anisotropy in the plane of Fe layer.
    Źródło:
    Acta Physica Polonica A; 2013, 124, 5; 873-876
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
    Tytuł:
    Mn Impurity in Bulk GaAs Crystals
    Autorzy:
    Pawłowski, M.
    Piersa, M.
    Wołoś, A.
    Palczewska, M.
    Strzelecka, G.
    Hruban, A.
    Gosk, J.
    Kamińska, M.
    Twardowski, A.
    Powiązania:
    https://bibliotekanauki.pl/articles/2044520.pdf
    Data publikacji:
    2005-11
    Wydawca:
    Polska Akademia Nauk. Instytut Fizyki PAN
    Tematy:
    71.55.Eq
    72.20.Ee
    75.50.Pp
    76.30.Fc
    Opis:
    Magnetic and electron transport properties of GaAs:Mn crystals grown by Czochralski method were studied. Electron spin resonance showed the presence of Mn acceptor A in two charge states: singly ionized A$\text{}^{-}$ in the form of Mn$\text{}^{2+}$(d$\text{}^{5}$), and neutral A$\text{}^{0}$ in the form of Mn$\text{}^{2+}$(d$\text{}^{5}$) plus a bound hole (h). It was possible to determine the relative concentration of both types of centers from intensity of the corresponding electron spin resonance lines. Magnetization measured as a function of magnetic field (up to 6 T) in the temperature range of 2-300 K revealed overall paramagnetic behavior of the samples. Effective spin was found to be about 1.5 value, which was consistent with the presence of two types of Mn configurations. In most of the studied samples the dominance of Mn$\text{}^{2+}$(d$\text{}^{5}$)+h configuration was established and it increased after annealing of native donors. The total value of Mn content was obtained from fitting of magnetization curves with the use of parameters obtained from electron spin resonance. In electron transport, two mechanisms of conductivity were observed: valence band transport dominated above 70 K, and hopping conductivity within Mn impurity band at lower temperatures. From the analysis of the hopping conductivity and using the obtained values of the total Mn content, the effective radius of Mn acceptor in GaAs was estimated as a = 11±3Å.
    Źródło:
    Acta Physica Polonica A; 2005, 108, 5; 825-830
    0587-4246
    1898-794X
    Pojawia się w:
    Acta Physica Polonica A
    Dostawca treści:
    Biblioteka Nauki
    Artykuł
      Wyświetlanie 1-8 z 8

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