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Magnetic domain wall mobility limitation by anisotropic impurity ions in ferrimagnetic insulators
Vol.5, No.5
ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS
dependent on the energy change and on the activation energy for the process. Because of the low activation energy involved, migration along areas of misorientation, such as grain boundaries and zones of dislocation, is the preferred explanation for the observed migration. (Received 15 December 1966) (Revised 27 March 1967) 15.
INFRARED LATTICE VIBRATIONS OF SINGLE CRYSTAL LITHIUM HYDRIDE AND SOME OF ITS ISOTOPIC DERIVATIONS M. H. Brodsky and E. Burstein (Physics Department and Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania)
The infrared reflection spectra of single crystal lithium hydride, lithium deuteride, lithium-6 hydride, and lithium-? hydride have been measured and analyzed. The long wavelength limits of the optical lattice vibrational frequencies have been determined and used to find the static dielectric constants and Szigeti effective charges of all the isotopic variations studied. It is found that the square of the longitudinal (or transverse) frequency is inversely proportional to the reduced mass of the ion pairs forming the crystal. The Szigeti effective charge for LiH, e”~= (0. 53 ± 0. 02)e, is qualitatively accounted for by the Dick and Overhauser shell model for the vibrating ions. A slight isotope effect on the e*. is noted in LiD and the difference in effective charges is interpretable within the framework of the shell model.
band gap is estimated to be 13. 60 ±0. 06 eV. A strong peak in the function Im(1/ c) near 25 eV is identified as a bulk plasma resonance, and is in agreement with published characteristic electron energy loss work on thin films. (Received 6 February 1967) (Revised 3 April 1967) PULSED NUCLEAR MAGNETIC RESONANCE STUDY OF IRRAD— IATED LITHIUM HYDRIDE P.C. Souers, T.A. Jolly and C. F. Cline (Lawrence Radiation Laboratory, University of California, Livermore, California) Lithium hydride doped with H3 expands by a sell-damaging process. Samples stored at 23, 70, 125, and 250°Cwere studied at 23°C with pulsed nuclear magnetic resonance. Motionally-narrowed signals were found for H1,H3, L’~ and He3. The numbers of nuclear spins in these signals were measured and compared with the fractional volumetric increase of the LiH. The intensity of H1 and H3 signals correlates with the initial swelling up to a growth of 25-30 volume percent. The build-up of He3 probably causes (the) later stage growth. Lithium metal precipitation increases with increasing temperature. 17.
The form of the free hydrogen in the lower temperature samples is unknown. In the 250°Csample the transverse relaxation time (T 2) is approximately equal to the spin-lattice relaxation time (T1), which is normally observed for hydrogen gas. (Received 1 January 1967) (Revised 3 April 1967)
(Received 24 February 1967) 18. 16.
ELECTRONIC SPECTRUM OF CRYSTALLINE LITHIUM FLUORIDE D. Roessler and W. C. Walker (Department of Physics, University of California, Santa Barbara, California 93106)
The reflection spectrum of freshly cleaved lithium fluoride has been measured from the near ultraviolet to 28 eV. The real (~ ~)and imaginary (e 2) parts of the dielectric response function have been computed via the KramersKronig relations. The F exciton band at 12. 61 eV (300°K)is asymmetric due to subsidiary structure, but its hall-width from a classical dispersion fit is about 0. 33 eV with a corresponding oscillator strength of 0.55 per molecule. The
v
MAGNETIC DOMAIN WALL MOBILITY LIMITATION BY ANISOTROPIC IMPURITY IONS IN FERRIMAGNETIC INSULATORS H. Harper and R. W. Teale (The Physics Department, The University, Sheffield, England)
A theory is given for the limitation of magnetic domain wall velocity in ferrimagnetic insulators due to the relaxation of constituent ions with anisotropic energy levels. For 10% Yb~ doped yttrium iron garnet the predicted velocity falls from 7 x lO~cm sec 1 oe 1 at 300°K to 20 cm sec oe ‘at 12°K,then rises sharply. Measurements of switching time on pure and 10% Yb doped Y. I. G. show the Impurity dominates the velocity limitation for 6°K
vi
ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS
experiments accords with theory here within the limits of the qualitative comparison. According to the theory the phenomenological damping constant determined from microwave resonance linewidth and wall velocity are predicted to agree, roughly, for high but not low T for such materials. The low wall velocity observed in pure Y.I.G. receives no explanation. (Received 27 December 1966) 19.
MAGNETIC PROPERTIES OF THE SPINEL SYSTEM Fe1 ~Cu~Cr2S4 Research 0. Haacke Division, and L. C. American Beegle (Central Cyanamid Company, Stamford, Connecticut) -
FeCr 2S4 and CuCr2S4 are found to form a series of solid solutions. Measurements of the temperature dependence of the magnetic susceptibility ~ and of the saturation magnetization in the Fe1_,, Cu~Cr2S4system reveal a complex transition from a ferrimagnetic spin ordering (FeCr2S4) to ferromagnetic interactions (CuCr2S4). The Curie-Weiss law is only obeyed for small and large x. In the intermediate concentration range, the l/x versus T curves do not have any linear portions. The number of Bohr magnetons per molecule also changes nonlinearly with composition. In order to explain the experimental data, it Is suggested that some of the chromium Ions are In the low-spin state. This low-spin state can be caused by local tngonal lattice distortions around those chromium ions which have on one side next-nearest copper ions and on the other side next-nearest iron ions, 20.
POLARIZATION OF LUMINESCENCE IN KBr:Tl TYPE CRYSTALS DUE TO
Vol.5, No. 5
THE JAHN-TELLER EFFECT A. Fukuda, S. Makishima, T. Mabuchi and R. Onaka (The Institute for Solid State Physics, The University of Tokyo Azabu, Minato-ku, Tokyo, Japan) Partially polarized luminescence 1~ A1~)is observed when excitation is made by linearly polarized light belonging to the A absorption band (A1 T1 ~)of the metal impurity ions 2~and with ~2 Pb2~)in electronKBr configurations crystals. The (Gadegree ~,In of Tl~,Sn polarization at low energy tail of the A band is larger than that at the high energy tail, i. e., it varies with the photon energy of exciting light. (T
-.
~,
The azimuthal dependence in the (100) plane becomes zero in the { 011 1 direction. The polarization tends to disappear at high temperatures. Arguments are given which make it seem likely that the observed polarization is due to the splitting of the degenerate excited state caused by non-totally-symmetric vibrations around the center, in other words, due to the dynamical Jahn-Teller effect. The processes in which the polarization is partially transferred from exciting light to emitted light are qualitatively discussed on the basis of the adiabatic potential energy surface of the T1~excited electronic state in the six dimensional (A1 E, and T2~)configuration coordinate space. The importance of the JahnTeller effect is also discussed in connection with the two emission bands excitable in the A absorption. ~,
(Received 29 November 1966) (Revised 21 March 1967)
ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS
dependent on the energy change and on the activation energy for the process. Because of the low activation energy involved, migration along areas of misorientation, such as grain boundaries and zones of dislocation, is the preferred explanation for the observed migration. (Received 15 December 1966) (Revised 27 March 1967) 15.
INFRARED LATTICE VIBRATIONS OF SINGLE CRYSTAL LITHIUM HYDRIDE AND SOME OF ITS ISOTOPIC DERIVATIONS M. H. Brodsky and E. Burstein (Physics Department and Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania)
The infrared reflection spectra of single crystal lithium hydride, lithium deuteride, lithium-6 hydride, and lithium-? hydride have been measured and analyzed. The long wavelength limits of the optical lattice vibrational frequencies have been determined and used to find the static dielectric constants and Szigeti effective charges of all the isotopic variations studied. It is found that the square of the longitudinal (or transverse) frequency is inversely proportional to the reduced mass of the ion pairs forming the crystal. The Szigeti effective charge for LiH, e”~= (0. 53 ± 0. 02)e, is qualitatively accounted for by the Dick and Overhauser shell model for the vibrating ions. A slight isotope effect on the e*. is noted in LiD and the difference in effective charges is interpretable within the framework of the shell model.
band gap is estimated to be 13. 60 ±0. 06 eV. A strong peak in the function Im(1/ c) near 25 eV is identified as a bulk plasma resonance, and is in agreement with published characteristic electron energy loss work on thin films. (Received 6 February 1967) (Revised 3 April 1967) PULSED NUCLEAR MAGNETIC RESONANCE STUDY OF IRRAD— IATED LITHIUM HYDRIDE P.C. Souers, T.A. Jolly and C. F. Cline (Lawrence Radiation Laboratory, University of California, Livermore, California) Lithium hydride doped with H3 expands by a sell-damaging process. Samples stored at 23, 70, 125, and 250°Cwere studied at 23°C with pulsed nuclear magnetic resonance. Motionally-narrowed signals were found for H1,H3, L’~ and He3. The numbers of nuclear spins in these signals were measured and compared with the fractional volumetric increase of the LiH. The intensity of H1 and H3 signals correlates with the initial swelling up to a growth of 25-30 volume percent. The build-up of He3 probably causes (the) later stage growth. Lithium metal precipitation increases with increasing temperature. 17.
The form of the free hydrogen in the lower temperature samples is unknown. In the 250°Csample the transverse relaxation time (T 2) is approximately equal to the spin-lattice relaxation time (T1), which is normally observed for hydrogen gas. (Received 1 January 1967) (Revised 3 April 1967)
(Received 24 February 1967) 18. 16.
ELECTRONIC SPECTRUM OF CRYSTALLINE LITHIUM FLUORIDE D. Roessler and W. C. Walker (Department of Physics, University of California, Santa Barbara, California 93106)
The reflection spectrum of freshly cleaved lithium fluoride has been measured from the near ultraviolet to 28 eV. The real (~ ~)and imaginary (e 2) parts of the dielectric response function have been computed via the KramersKronig relations. The F exciton band at 12. 61 eV (300°K)is asymmetric due to subsidiary structure, but its hall-width from a classical dispersion fit is about 0. 33 eV with a corresponding oscillator strength of 0.55 per molecule. The
v
MAGNETIC DOMAIN WALL MOBILITY LIMITATION BY ANISOTROPIC IMPURITY IONS IN FERRIMAGNETIC INSULATORS H. Harper and R. W. Teale (The Physics Department, The University, Sheffield, England)
A theory is given for the limitation of magnetic domain wall velocity in ferrimagnetic insulators due to the relaxation of constituent ions with anisotropic energy levels. For 10% Yb~ doped yttrium iron garnet the predicted velocity falls from 7 x lO~cm sec 1 oe 1 at 300°K to 20 cm sec oe ‘at 12°K,then rises sharply. Measurements of switching time on pure and 10% Yb doped Y. I. G. show the Impurity dominates the velocity limitation for 6°K
vi
ABSTRACTS OF PAPERS TO APPEAR IN J. PHYS. CHEM. SOLIDS
experiments accords with theory here within the limits of the qualitative comparison. According to the theory the phenomenological damping constant determined from microwave resonance linewidth and wall velocity are predicted to agree, roughly, for high but not low T for such materials. The low wall velocity observed in pure Y.I.G. receives no explanation. (Received 27 December 1966) 19.
MAGNETIC PROPERTIES OF THE SPINEL SYSTEM Fe1 ~Cu~Cr2S4 Research 0. Haacke Division, and L. C. American Beegle (Central Cyanamid Company, Stamford, Connecticut) -
FeCr 2S4 and CuCr2S4 are found to form a series of solid solutions. Measurements of the temperature dependence of the magnetic susceptibility ~ and of the saturation magnetization in the Fe1_,, Cu~Cr2S4system reveal a complex transition from a ferrimagnetic spin ordering (FeCr2S4) to ferromagnetic interactions (CuCr2S4). The Curie-Weiss law is only obeyed for small and large x. In the intermediate concentration range, the l/x versus T curves do not have any linear portions. The number of Bohr magnetons per molecule also changes nonlinearly with composition. In order to explain the experimental data, it Is suggested that some of the chromium Ions are In the low-spin state. This low-spin state can be caused by local tngonal lattice distortions around those chromium ions which have on one side next-nearest copper ions and on the other side next-nearest iron ions, 20.
POLARIZATION OF LUMINESCENCE IN KBr:Tl TYPE CRYSTALS DUE TO
Vol.5, No. 5
THE JAHN-TELLER EFFECT A. Fukuda, S. Makishima, T. Mabuchi and R. Onaka (The Institute for Solid State Physics, The University of Tokyo Azabu, Minato-ku, Tokyo, Japan) Partially polarized luminescence 1~ A1~)is observed when excitation is made by linearly polarized light belonging to the A absorption band (A1 T1 ~)of the metal impurity ions 2~and with ~2 Pb2~)in electronKBr configurations crystals. The (Gadegree ~,In of Tl~,Sn polarization at low energy tail of the A band is larger than that at the high energy tail, i. e., it varies with the photon energy of exciting light. (T
-.
~,
The azimuthal dependence in the (100) plane becomes zero in the { 011 1 direction. The polarization tends to disappear at high temperatures. Arguments are given which make it seem likely that the observed polarization is due to the splitting of the degenerate excited state caused by non-totally-symmetric vibrations around the center, in other words, due to the dynamical Jahn-Teller effect. The processes in which the polarization is partially transferred from exciting light to emitted light are qualitatively discussed on the basis of the adiabatic potential energy surface of the T1~excited electronic state in the six dimensional (A1 E, and T2~)configuration coordinate space. The importance of the JahnTeller effect is also discussed in connection with the two emission bands excitable in the A absorption. ~,
(Received 29 November 1966) (Revised 21 March 1967)