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  • 1995-1999  (24)
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  • 1
    Electronic Resource
    Electronic Resource
    Study of the cation distribution in the surface layer and bulk of substituted iron garnet films (1997)
    Springer
    Physics of the solid state 39 (1997), S. 1108-1111 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A comparative analysis has been carried out of the physical-chemical state of the surface and bulk of single-crystal films of the iron garnet Y2.6Sm0.4Fe3.7Ga1.3O12 on substrates consisting of a gadolinium-gallium garnet single crystal. To carry out this study, we used the method of simultaneous γ-ray, x-ray, and electron Mösbauer spectroscopy, which made it possible to simultaneously extract information from the surface layers and the bulk of the sample. This method was applied using a precision system for the motion for the Mössbauer source. It is shown that the parameters of the hyperfine interactions in the surface layer and in the bulk of the film differ, and that these differences increase towards the surface. This result is explained by the fact that the surface layer is formed as the substrate, together with the synthesized film, is removed from the flux and, consequently, the temperature conditions of synthesis of the bulk and of the surface layer are different.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130025
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  • 2
    Electronic Resource
    Electronic Resource
    Study of the magnetic state of a highly dispersed BaO · 6Fe2O3 system with near-critical particle size (1998)
    Springer
    Physics of the solid state 40 (1998), S. 1178-1181 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract An investigation was made of the magnetic state of a system of highly anisotropic BaO · 6Fe2O3 nanocrystals several lattice parameters thick and having a near-critical volume (∼10−18 cm3), obtained using cryochemical technology. It is observed that the particles are transformed to the superparamagnetic state and it is shown that the external magnetic field plays a role in its formation. An H-T diagram was obtained for the temperature range 300 K-T c, which shows various regions uncharacteristic of the macro-object, which are specifically attributed to the distribution over the anisotropy fields in the system and the impaired magnetic structure in the surface zone of the particles. Relatively large regions of magnetic fields and temperatures were observed where reversible rotation of the magnetization vector of particles with near-critical volume plays an important role.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130514
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  • 3
    Electronic Resource
    Electronic Resource
    Studies of the surface magnetic state of the Sr-M hexagonal ferrites near the phase transition at the Curie temperature (1999)
    Springer
    Physics of the solid state 41 (1999), S. 420-425 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A study is reported of the temperature dependences of the hyperfine (HF) interaction parameters in a ∼200-nm thick surface layer and in the bulk of macroscopic hexagonal ferrite crystals of the Sr-M type (SrFe12O19 and SrFe10.2Al1.8O19). The method used for the measurements is Mössbauer spectroscopy with simultaneous detection of gamma quanta, characteristic x-ray emission, and electrons, which permits direct comparison of the HF parameters in the bulk and the near-surface layers of a sample. As follows from the experimentally determined temperature dependences of the effective magnetic fields, the fields at the nuclei of the iron ions located in a ∼200-nm thick near-surface layer decrease with increasing temperature faster than those of the ions in the bulk. The transition to paramagnetic state in a ∼200-nm thick surface layer was found to occur 3° below the bulk Curie temperature. This offers the first experimental evidence for the transition to paramagnetic state in a surface layer of macroscopic ferromagnets to take place below the Curie temperature T c for the bulk of the crystal. It has been established that the transition temperature T c (L) of a thin layer at a depth L from the surface of a crystal increases as one moves away from the surface to reach T c at the inner boundary of the surface layer called critical. In the vicinity of T c one observes a nonuniform state, with the crystal being magnetically ordered in the bulk but disordered on the surface. The experimental data obtained were used to construct a phase diagram of surface and bulk states for macroscopic magnets near the Curie (or Néel) temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130795
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  • 4
    Electronic Resource
    Electronic Resource
    Simultaneous gamma, x-ray, and electron Mössbauer spectroscopy of the volume and surface magnetic structure of hexagonal M-ferrites (1997)
    Springer
    Journal of experimental and theoretical physics 84 (1997), S. 788-793 
    Details
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Direct comparative studies are made between the magnetic structures of a surface layer of thickness ∼40 nm and the bulk magnetic structure of ferromagnetic single crystals of hexagonal M ferrites (BaFe12O19, SrFe12O19, PbFe12O19) with a magneto-plumbite structure. Measurements are made by simultaneous gamma, x-ray, and electron Mössbauer spectroscopy in order to investigate the properties of the surface layer and the bulk crystal simultaneously. Experimental data obtained with a depth resolution of ∼ 10 nm show that the orientation of the magnetic moments of the iron ions (along the crystallographic c axis) does not change on approaching the surface from the crystal volume. Thus, to within an experimental error of ∼ 10 nm, single crystals of the hexagonal ferrites BaFe12O19, SrFe12O19, and PbFe12O19 with a ferromagnetic structure do not have a “ transition” surface layer whose magnetic structure differs from that of the bulk crystal such as that which exists, with a depth of several hundred nm, in antiferromagnetic materials with weak ferromagnetism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.558212
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  • 5
    Electronic Resource
    Electronic Resource
    Mössbauer studies of the surface and bulk properties of substituted iron-garnet films in the vicinity of the Curie point (1997)
    Springer
    Physics of the solid state 39 (1997), S. 1251-1254 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The magnetic properties of the surface layer and bulk of iron-garnet films of composition Y2.6Sm0.4Fe3.7Ga1.3O12, grown by liquid-phase epitaxy on substrates of a gadolinium-gallium garnet single crystal, are investigated. The method of simultaneous gamma-ray, x-ray, and electron Mössbauer spectroscopy is used for the investigations. It is found that the temperature T c(L) of the transition to the paramagnetic state of a thin layer localized at a depth L below the surface within ∼300 nm decreases smoothly with decreasing distance from the surface. The causes of the difference between the temperature of the transition to the paramagnetic state in the surface layer and that bulk of the film are: 1) variation of the degree of substitution of gallium for iron in the surface layer; 2) weakening of exchange interactions at the surface of the sample.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130055
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetic anisotropy of a system of nanocrystalline BaO·6Fe2O3 particles (1998)
    Springer
    Physics of the solid state 40 (1998), S. 1718-1720 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The anisotropy of a system of barium ferrite particles with an average diameter of 60 nm has been studied. The effective anisotropy constant has been determined in the temperature range from 4.2 K to T c by the law governing approach to saturation magnetization. The observed deviation from the magnetocrystalline anisotropy constant is explained as due to a negative contribution of the “surface” anisotropy constant. An estimate is made of this contribution as a function of particle size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130642
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  • 7
    Electronic Resource
    Electronic Resource
    Surface magnetism of Sc-substituted Ba-M hexaferrites (1999)
    Springer
    Journal of experimental and theoretical physics 89 (1999), S. 890-898 
    Details
    ISSN: 1090-6509
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A technique of simultaneous gamma-ray, x-ray, and electron Mössbauer spectroscopy is used to study the magnetic structure of the surface layer with direct comparison to the magnetic structure inside single crystal samples of hexagonal Ba-M ferrites, in which part of the iron ions have been replaced by diamagnetic Sc ions (chemical formula BaFe12−δ ScδO9). It is found that when the diamagnetic Sc ions are introduced into the crystal lattice of BaFe12−δ ScδO19 at concentrations (x=0.4 and 0.6) far below the level at which the collinear magnetic structure inside the sample is destroyed, a macroscopic layer of thickness ∼300 nm develops on the surface, in which the magnetic moments of the iron ions are oriented noncollinearly with respect to the moments inside the sample. The deviation 〈θ〉 of the magnetic moments in BaFe11.6Sc0.4O19 was 10° ± 62° for x=0.4, and when the Sc concentration was raised to 0.6, the angle 〈θ〉 increased to 17° ± 62°. The noncollinear magnetic structure in the surface layer in these crystals develops because of further reduction in the energy of the exchange interactions owing to the presence of a “defect,” such as the surface. For the first time, therefore, an anisotropic surface layer whose magnetic properties differ from those in the interior of a sample has been observed experimentally in ferromagnetic crystals, as predicted by Néel [L. Néel, Phys. Radium. 15, 225 (1954)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.558929
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  • 8
    Electronic Resource
    Electronic Resource
    Mössbauer studies of the surface and bulk magnetic structure of scandium-substituted Ba-M-type hexaferrites (1999)
    Springer
    Physics of the solid state 41 (1999), S. 433-439 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A direct comparison of the magnetic structures of a surface layer and of the bulk of Ba-M-type hexagonal ferrites with iron ions partially replaced by Sc diamagnetic ions (BaFe12−x ScxO19) has been made by simultaneous Mössbauer spectroscopy with detection of gamma rays, characteristic x-ray emission, and electrons. It has been found that, if the magnetic lattice of a Ba-M-type hexagonal ferrite is weakly diluted by Sc diamagnetic ions, a ∼300-nm thick macroscopic layer forms on the surface of a BaFe11.4Sc0.6O19 crystal, in which the iron-ion magnetic moments are noncollinear with the moments in the bulk. The noncollinear magnetic structure forms in the near-surface layer of BaFe12−x ScxO19 crystals because the exchange interaction energy is additionally reduced by the presence of such a “defect” as the surface. This is the first observation in ferromagnetic crystals of an anisotropic surface layer whose magnetic properties, as predicted by Néel, differ from those of the bulk.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1130797
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  • 9
    Electronic Resource
    Electronic Resource
    Investigations of the magnetic structure of the surface and volume of aluminum-substituted Sr-M type hexaferrites (1998)
    Springer
    JETP letters 67 (1998), S. 843-848 
    Details
    ISSN: 1090-6487
    Keywords: 75.70.Ak ; 75.50.Dd
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The magnetic structure of the surface layer of single crystals of hexagonal ferrites of the type Sr-M (SrFe12O19) in which some iron ions are replaced by diamagnetic Al ions is investigated, in direct comparison with the magnetic structure in the bulk of the sample, by the method of simultaneous gamma, x-ray, and electron Mössbauer spectroscopy. It is found that under conditions of diamagnetic dilution of the magnetic lattice of hexagonal ferrites of the type Sr-M by Al ions, a layer ~200 nm thick in which the orientation of the magnetic moments is not collinear with the direction of the moments in the bulk of the sample is observed on the surface of SrFe10.2Al1.8O19 crystals. Thus a “transitional” surface layer has been observed on macroscopic ferromagnetic crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567759
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  • 10
    Electronic Resource
    Electronic Resource
    Magnetic states of the surface and bulk of ferrites near a phase transition at the Curie temperature (1999)
    Springer
    JETP letters 69 (1999), S. 57-63 
    Details
    ISSN: 1090-6487
    Keywords: 75.50.Bb ; 75.30.Kz ; 75.40.−s
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Investigations of the magnetic state of a surface layer ~200 nm thick and of the bulk in macroscopic ferrite crystals of the type Ba-M (BaFe12O19) are performed in the phase transition region around the Curie temperature (T c). The method of simultaneous gamma, x-ray, and electron Mössbauer spectroscopy, which made it possible to compare directly the phase states of the surface and bulk of the sample, is used for the measurements. It is observed experimentally that in BaFe12O19 the transition of a surface layer ~200 nm thick to the paramagnetic state occurs at temperatures below T c. It is established that the transition temperature T c(L) of a thin layer localized at depth L from the surface of the crystal increases with distance from the surface and reaches the value T c at the lower boundary of the “critical” surface layer. Therefore, near T c a nonuniform state in which the crystal is magnetically ordered in the bulk but disordered at the surface is observed. A phase diagram of the states of the surface and of the bulk of macroscopic magnets near the Curie (or Néel) point is proposed on the basis of all the experimental results obtained in the present work as well as previously published results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.567984
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