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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
    Lowering of magnetic field intensity at the surfaces of α-Fe2O3 and FeBO3 single crystals (2000)
    Springer
    JETP letters 71 (2000), S. 134-137 
    Details
    ISSN: 1090-6487
    Keywords: 75.70.Ak ; 76.80.+y
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Depth-selective conversion electron Mössbauer spectroscopy was used to study magnetic properties of the thin surface layers of the α-Fe2O3 and FeBO3 single crystals. An analysis of the experimental spectra indicates that the magnetic properties of the layers at a depth of more than ∼100 nm from the surface are similar to the properties of crystal bulk, and the corresponding spectra consist of narrow lines. The lines gradually broaden as the crystal surface is approached. The spectra of the ∼10-nm-thick surface layers consist of broad lines, indicating a wide distribution δ=2.1 T of the effective magnetic field about its mean value of 32.2(4) T. The experimental spectra were used to determine the effective magnetic fields (H eff) for the iron ions situated in the surface layers of thickness ∼100 nm. The effective fields in these layers were found to gradually decrease at room temperature (291 K) as the crystal surface was approached. The H eff values in the 2.4(9)-nm-thick surface layer of the α-Fe2O3 crystal and 4.9(9)-nm layer of FeBO3 are 0.7(2) and 1.2(3)%, respectively, smaller than for the nuclei of the ions in the bulk of these crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.568298
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  • 3
    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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  • 4
    Electronic Resource
    Electronic Resource
    Influence of surface on the effective magnetic fields in α-Fe2O3 and FeBO3 (2000)
    Springer
    Physics of the solid state 42 (2000), S. 1691-1695 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract First measurements of the effective magnetic fields as a function of the depth at which the iron ions are in the surface layer of α-Fe2O3 and FeBO3 single crystals are reported. The method used is the depth-selective conversion-electron Mössbauer spectroscopy. An analysis of experimental spectra revealed that the magnetic properties of the crystal surface vary smoothly from the bulk to surface characteristics within a layer ∼100 nm thick. The layers lying below ∼100 nm from the surface are similar in properties to the bulk of the crystal, and their spectra consist of narrow lines. The spectral linewidths increase smoothly as one approaches the crystal surface. The spectra obtained from a ∼10-nm thick surface layer consist of broad lines indicating a broad distribution of effective magnetic fields. Calculations show that the field distribution width in this layer is δ=2.1(3) T, for an average value H eff=32.2(4) T. It has been experimentally established that, at room temperature (291 K), the effective magnetic fields smoothly decrease as one approaches the crystal surface. The effective fields in a 2.4(9)-nm surface layer of α-Fe2O3 crystals are lower by 0.7(2)% than the fields at the ion nuclei in the bulk of the sample. In the case of FeBO3, the effective fields decrease by 1.2(3)% in a surface layer 4.9(9) nm thick.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1309453
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  • 5
    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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  • 6
    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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  • 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
    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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  • 9
    Electronic Resource
    Electronic Resource
    Surface magnetism of Al-substituted Sr-M-type hexagonal ferrites (1999)
    Springer
    Physics of the solid state 41 (1999), S. 1658-1664 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The surface and bulk magnetic structures of Sr-M-type single-crystal hexagonal ferrites (with the chemical formula SrFe12−x AlxO19) have been directly compared by simultaneous gamma, x-ray, and electron Mössbauer spectroscopy. It was found, that when the magnetic lattice of Sr-M hexagonal ferrites is slightly diluted by diamagnetic Al ions, namely, for x=1.8 (SrFe10.2Al1.8O19), a ∼300-nm thick macroscopic anisotropic layer forms on the crystal surface, wherein iron-ion magnetic moments are oriented differently from those in the bulk of the sample. The reason for the onset of a noncollinear magnetic structure in the surface layer of SrFe10.2Al1.8O19 crystals is the additional lowering of the exchange interaction energy caused by the presence of such a “defect” as the surface. Thus an anisotropic surface layer predicted theoretically by L. Néel in 1954 has been detected in ferromagnetic crystals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1131049
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  • 10
    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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