The reflection properties of 300 nm periodically structured silicon surfaces with depth varying between 35 and 190 nm, prepared by interference lithography, were examined in the range 200 nm<λ<3000 nm. A decrease in the reflectivity that becomes stronger with increasing structure depth is observed below 1000 nm. This broad-band reduction is caused by diffraction effects at short wavelengths and by the `moth-eye effect' at long wavelengths. The results show a universal behaviour in the optical-path to wavelength ratio dependence of the reflectivity and are in good agreement with the results obtained for the `moth-eye effect' from the effective medium theory.

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The presence of a large inverse magnetocaloric effect around the martensitic transformation in Ni-Mn-Sn and Ni-Mn-In alloys is expected to lead to substantial cooling on applying a magnetic field. However, the occurrence of hysteresis around the transition causes limitations on adiabatic temperature-changes. We study the adiabatic temperature-change in both systems in relation to the hysteresis effects. Ni-Mn-In, having a relatively narrower hysteresis and a greater shift of the characteristic transition temperatures with applied field with respect to Ni-Mn-Sn, shows reversibility in the adiabatic-temperature change related to the inverse magnetocaloric effect when the state of the system is cycled within a minor transitional hysteresis loop. Ni-Mn-Sn does not show reversibility in the inverse magnetocaloric effect under cycling-fields up to 5 T. The reversibility in the adiabatic temperature-change is directly related to the reversibility in the relative amount of austenite and martensite in the sample when the field is cycled.

Neutron scattering and ultrasonic methods have been used to study the lattice dynamics of two single crystals of Ni-Mn-In Heusler alloys close to Ni 50 Mn 34 In 16 magnetic superelastic composition. The paper reports on the experimental determination of the low-lying phonon-dispersion curves and the elastic constants for this alloy system. We found that the frequencies of the TA 2 branch are relatively low and it exhibits a small dip anomaly at a wave number ξ 0 ≈1/3, which softens with decreasing temperature. Associated with the softening of this phonon, we also observed the softening of the shear elastic constant C′=(C 11 −C 12 )/2. Both temperature softenings are typical for bcc-based solids which undergo martensitic transformations and reflect the dynamical instability of the cubic lattice against shearing of {110} planes along ⟨11̅ 0⟩ directions. Additionally, we measured low-lying phonon-dispersion branches and elastic constants in applied magnetic fields aimed to characterize the magnetoelastic coupling. Disciplines Condensed Matter Physics | Metallurgy CommentsThis article is from Physical Review B 79 (2009) Neutron scattering and ultrasonic methods have been used to study the lattice dynamics of two single crystals of Ni-Mn-In Heusler alloys close to Ni 50 Mn 34 In 16 magnetic superelastic composition. The paper reports on the experimental determination of the low-lying phonon-dispersion curves and the elastic constants for this alloy system. We found that the frequencies of the TA 2 branch are relatively low and it exhibits a small dip anomaly at a wave number 0 Ϸ 1 / 3, which softens with decreasing temperature. Associated with the softening of this phonon, we also observed the softening of the shear elastic constant CЈ = ͑C 11 − C 12 ͒ / 2. Both temperature softenings are typical for bcc-based solids which undergo martensitic transformations and reflect the dynamical instability of the cubic lattice against shearing of ͕110͖ planes along ͗110͘ directions. Additionally, we measured low-lying phonon-dispersion branches and elastic constants in applied magnetic fields aimed to characterize the magnetoelastic coupling.

Pulse‐echo‐overlap measurements of ultrasonic wave velocity have been used to determine the dependences of the elastic stiffness moduli of polycrystalline cementite (Fe3C) on temperature in the range 75–295 K and hydrostatic pressure up to 0.1 GPa at room temperature. The longitudinal stiffness (CL) and adiabatic bulk modulus (BS) stiffen, while the shear stiffness (μ) and Young's modulus (E) soften with decreasing temperature. The ultrasonic velocities increase approximately linearly with pressure, much more steeply for the longitudinal than the shear mode. The values obtained at 295 K for the hydrostatic‐pressure derivatives (∂CL/∂P)P=0, (∂μ/∂P)P=0 and (∂BS/∂P)P=0 of cementite are 7.9 ± 1.7, 1.4 ± 0.1 and 6.1 ± 1.7, respectively: the zone‐centre acoustic phonons stiffen under pressure. The longitudinal (γL), shear (γS) and mean (γel) acoustic‐mode Grüneisen parameters of cementite are positive; γS is markedly smaller than γL indicating that the shear acoustic modes are less anharmonic than the longitudinal modes.