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  • 1
    Electronic Resource
    Electronic Resource
    Simultaneous surface and bulk magnetic properties investigations by using simultaneous gamma, x-rays and conversion electron Mössbauer spectroscopy: Method and experimental results : The 6th joint magnetism and magnetic materials (MMM)-intermag conference (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 7099-7101 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The surface and bulk phase transitions in a microscopic antiferromagnetic Fe3BO6 crystal was investigated by means of new method: Simultaneous gamma rays, x-rays, and electron Mössbauer spectroscopy (A. S. Kamzin, V. P. Rusakov, and L. A. Grigor'ev, in Proceedings of the International Conference "Physics of transition metals,'' USSR-1988, Part 2, p. 271; A. S. Kamzin, and L. A. Grigor'ev, Pisma Zh. Tekh. Fiz. 16, 38 (1990) [Sov. Tech. Fiz. Lett. 16, 417 (1990)]), which makes it possible to study simultaneously the surface and volume properties of a bulk crystal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358040
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  • 2
    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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  • 3
    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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  • 4
    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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  • 5
    Electronic Resource
    Electronic Resource
    Critical behavior of the surface of FeBO3 single crystals (2000)
    Springer
    JETP letters 71 (2000), S. 442-445 
    Details
    ISSN: 1090-6487
    Keywords: 75.30.Kz ; 75.40.−s ; 68.35.Rh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The behavior of the surface and near-surface layers of macroscopic FeBO3 single crystals is studied over the temperature range from 291 K to Neél temperature (T N ) using depth-selective conversion-electron Mössbauer spectroscopy. Three different phases or states, namely, an antiferromagnetically ordered phase (similar to the crystal bulk state), a surface phase, and a transition layer between them coexist near the Neél point in a surface layer ∼500 nm thick. The critical parameters found for the bulk phase agree well with the theoretical critical index νth≅0.63 predicted by the 3D Ising model. As the crystal surface is approached, the critical parameter β increases to 0.51(2) but remains smaller than the value of β=0.8 for the surface of a semi-infinite Heisenberg model. Therefore, the effective dimensionality of the system, being equal to 3 in the bulk, decreases at the crystal surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.568373
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  • 6
    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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  • 7
    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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  • 8
    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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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Depth-selective conversion-electron Mössbauer spectroscopy of the surface of Ba-M hexaferrite single crystals (2000)
    Springer
    Physics of the solid state 42 (2000), S. 897-902 
    Details
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The magnetic properties of a 50-to 2-nm-thick surface layer in hexagonal ferrite BaFe12O19 single crystals are investigated for the first time. Measurements are made on a conversion-electron Mössbauer spectrometer constructed on the basis of a unique ultrahigh-vacuum magnetostatic electron analyzer of the “orange” type. An analysis of the experimental Mössbauer spectra obtained from the surface layer of BaFe12O19 50-to 2-nm-thick single crystals reveals that (1) the spectral line widths are close to the natural widths of Mössbauer lines and neither changes nor a set of the values of effective magnetic fields, as well as a paramagnetic state of iron ions, could appear due to a defect such as the “surface,” and (2) the experimental spectra are best described only under the assumption that the surface of a hexaferrite BaFe12O19 single crystal contains a 2-nm-thick layer, in which the magnetic moments of iron ions are deflected through ∼20° from the crystallographic C axis along which the magnetic moments of ions located in the bulk of the crystal are oriented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1131309
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