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Magnetic properties of Ni-Mn-Ga Heusler alloy films
Dubowik, J.,Goś,ciań,ska, I.,Kudryavtsev, Y. V.,Lee, Y. P.,Sová,k, P.,Konĉ,, M. WILEY-VCH Verlag 2006 Physica Status Solidi C Vol.3 No.1
<P>The films with composition Ni<SUB>x </SUB>Mn<SUB>y </SUB>Ga<SUB>z </SUB> (x = 50 ± 5, y = 25 ± 5, z = 25 ± 5) were deposited by flash-evaporation or sputtering on mica and glass substrates and annealed in a high vacuum at 673–973 K. X-ray diffraction at room temperature reveals the presence of B2 (or L2<SUB>1</SUB>) type of structure depending on annealing conditions. Magnetic properties were studied by ferromagnetic resonance at temperatures from 78 K to 400 K and compared with electric resistivity data. It is shown that the magnetic properties of the films critically depend on their structural ordering and microstructure. The films annealed at T < 800 K reveal a complex magnetic behavior due to their specific microstructure while those annealed at T > 800 K show magnetic properties comparable with those of bulk Ni-Mn-Ga alloys. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)</P>
Enhanced spin-wave damping in exchange-biased films
Janusz Dubowik,F. Stobiecki,I. Goscianska,이영백,A. Paetzold,K. Roll 한국물리학회 2004 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.45 No.1
The temperature dependencies of the ferromagnetic resonance (FMR) linewidth and the resonance eld shift have been investigated for NiO/NiFe exchange biased bilayers from 78 K to 500 K. A broad maximum in the linewidth at 500 Oe, solely due to the exchange-bias, is observed at 150 K when the magnetic eld is applied along the lm plane. When the magnetic eld is applied perpendicular to the lm plane, the maximum in the linewidth is less pronounced and amounts to be 100 Oe at the same temperature. Such a behavior of the FMR linewidth is accompanied by a monotonic increase in the negative resonance eld shift with decreasing temperature. Our results are compared with the previous experimental FMR and Brillouin light scattering data for various ferromagnetic/antiferromagnetic (FM/AF) structures, and suggest that spin dynamics (spin-wave damping and anomalous resonance eld-shift) in the FM/AF structures can be described in a consistent way by a single mechanism of so-called slow relaxation.
J. Dubowik,Y. V. Kudryavtsev,Y. P. Lee 한국자기학회 2004 Journal of Magnetics Vol.9 No.2
Polycrystalline Ni-Mn-Ga films have been deposited onto mica substrates held at 720 K by flash-evaporation method. At room temperature the films have a tetragonal structure with a = b = 0.598 and c = 0.576 ㎚ typical for bulk Ni₂MnGa below a martensitic transformation. Temperature measurements of ferromagnetic resonance reveal a martensitic phase transformation at 310 K. The transformation brings about a substantial decrease in the effective magnetization and a drastic increase in the ferromagnetic resonance linewidth due to a strong increase in the magnetic anisotropy in the martensitic phase.
Ferromagnetic Resonance Studies of Ultrathin Co Layers in Co / Ag Multilayers
J. Dubowik 한국자기학회 1999 Journal of Magnetics Vol.4 No.3
A relationship between microstructure and ferromagnetic resonance of Co/Ag multilayers has been studied in as-deposited and annealed multilayers with ultrathin (d_(Co) < 1 ㎚) Co layers. Depending on the nominal thickness of Co Co/Ag multilayers represent a system of fine magnetic particles (d_(Co) < 0.4 ㎚) or discontinuous layered structure (d_(Co)/0.5 ㎚). FMR data has been interpreted in the framework of a model of interacting fine particles exhibiting superparamagnetic behavior. Changes in the FMR spectra upon annealing have been attributed to the growth of the Co particles and to a transition from the fcc to hcp atomic structure of the highly (111) textured Co particles.
F. Stobiecki,T. Luciński,J. Dubowik,B. Szymański,M. Urbaniak,F. J. Castano,T. Stobiecki 한국자기학회 1998 Journal of Magnetics Vol.3 No.3
The magnetisation behaviour of polycrystalline permalloy/copper multilayers with mixed antiferromagnetic/ferromagnetic coupling was investigated as function of temperature. The results are discussed in a framework of a realistic model of anitferromagnetically coupled layers connected by ferromagnetic pinholes. A microstructure of pinholes (their density and dimensions) was varied either by a proper annealing treatment or by choosing samples with various Cu spacer thicknesses. It was demonstrated that the temperature changes of the net magnetic moment measured in a magnetic field smaller than the saturation field was strongly affected by the composition of the pinholes, their density, cross-sectional area and their lengths.