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6 Acta Physica Polonica A

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Structural and Magnetic Dynamical Properties of Solids. Experimental Approach with Inelastic Neutron Scattering

100%

Hennion B.

Acta Physica Polonica A

1999

tom 96

nr 5

629-640

Inelastic neutron scattering on single crystals is a privileged way to obtain valuable information on dynamical properties of solids. The basis of the technique is summarised. Master formulae and experimental examples for lattice dynamics and spin dynamics studies are presented.

Inelastic Neutron Scattering in γ-Mn(12%Ge) Alloy Above and Below the Néel Temperature

51%

Jankowska-Kisielińska J. , Mikke K. , Hennion B.

Acta Physica Polonica A

2000

tom 97

nr 3

559-562

The magnetic excitations different from spin waves in the γ-Mn(12%Ge) antiferromagnet are the subject of the present investigation. The inelastic neutron scattering was measured at 4 temperatures above T_{N}. The Lorentzian-type formula for the inelastic neutron scattering cross-section with the spectral width for a hydrodynamic region was used for data analysis. The obtained values of the "stiffness constants" are of the order of 200 meV Å and they depend weakly on temperature in the range of 1.04-1.25T_{N}. The inelastic neutron scattering for energy transfers below and close to the value of the gap energy of the spin wave spectrum was measured at room temperature. The observed intensities can be treated as a sum of intensities of neutrons scattered on spin waves around the magnetic Brillouin zone centre and = those scattered on fluctuations at the zone boundary.

Temperature Dependence of Magnetic Inelastic Neutron Scattering in Mn(12%Ge) Alloy

45%

Jankowska-Kisielińska J. , Mikke K. , Milczarek J. J. , Hennion B. , Udovenko V. A.

Acta Physica Polonica A

1997

tom 91

nr 2

483-486

A systematic study of temperature dependence of magnetic inelastic neutron scattering for itinerant antiferromagnet Mn(12%Ge) is presented. At low temperatures the experimental data are well described in terms of damped spin waves. This description becomes insufficient at least 150 K below T_{N}. In the temperature range 200-400 K the integrated intensity of distribution for energy transfer 13 THz increases by one third and the shape of the deconvoluted neutron scattering cross-section changes. These changes suggest that ca. 200 K below T_{N} an additional contribution to the inelastic neutron scattering starts to appear and that its origin is different from spin waves.

Lattice Dynamics of Cubic Mercury Sulphide

38%

Szuszkiewicz W. , Dybko K. , Dynowska E. , Górecka J. , Witkowska B. , Hennion B.

Acta Physica Polonica A

1996

tom 90

nr 5

947-950

The acoustic phonon dispersion of mercury sulphide of zinc-blende structure (β-HgS) was studied by inelastic neutron scattering. The measurements were carried out at 19 K and 295 K on HgS crystals doped with Fe. A slight decrease in phonon frequencies with increasing temperature was found, the temperature dependence being the strongest for LA phonons with [ξ,ξ,0] propagation. From acoustic phonon dispersion the values of selected elastic constants were determined for β-HgS.

Selected Properties of Lattice Dynamics of HgSe and β-HgS

32%

Szuszkiewicz W. , Dybko K. , Dynowska E. , Górecka J. , Witkowska B. , Hennion B. , Jouanne M. , Julien C.

Acta Physica Polonica A

1997

tom 92

nr 5

1029-1032

Optical phonon dispersion for β-HgS was measured by the neutron scattering for the first time. The results confirmed theoretically predicted anomalous behavior of phonon modes in this material, resulting probably from high ionicity of mercury sulphide and large difference of Hg and S atomic mass. Influence of the isotopic effects on the TO-phonon mode for HgSe and HgS is analyzed. The possible observation of such effects in IR reflectivity spectra taken for HgSe at low temperature is discussed.

Magnons in Cubic MBE-Grown A_{1-x}Mn_{x}Te Layers (A = Cd, Zn, Mg)

32%

Szuszkiewicz W. , Hennion B. , Jouanne M. , Morhange J. , Dynowska E. , Janik E. , Wojtowicz T. , Zieliński M. , Furdyna J.

Acta Physica Polonica A

1998

tom 94

nr 3

583-587

One-magnon excitations in MBE-grown A_{1-x}Mn_{x}Te layers (where A = Cd, Zn, Mg and x>0.7) were investigated by means of the Raman scattering measurements at low temperatures (≈20 K). The composition dependence of the anisotropy energy - as extracted from these measurements - is discussed. Further, the elastic neutron scattering measurements were performed in layers of cubic MnTe, which constitute the end point material of the ternary alloys series. Abundance of variously oriented antiferromagnetic domains in MnTe layers as a function of temperature was studied. We confirm occurrence of a pronounced magnetostriction effect.