The structural and magnetic properties of Mn5Ge3Cx films prepared at elevated substrate temperatures TS are investigated. In particular, films with x ≥ 0.5 and TS = 680 K exhibit a strongly enhanced Curie temperature TC = 440 K compared to Mn5Ge3 with TC = 304 K. Structural analysis of these films suggests that the carbon is interstitially incorporated into the voids of Mn octahedra of the hexagonal Mn5Si3-type structure giving rise to a lattice compression. The enhanced ferromagnetic stability in connection with the lattice compression is interpreted in terms of an Mn-Mn interaction mediated by C based on a change in the electronic structure.
COMMUNICATIONS materials causes the condensation of the silicate layers, giving the zeolite structures MCM-22 and ferrierite. Similar behavior can also be expected for RUB-15, since the silicate layer terminated with silanol groups should be the perfect subunit for the formation of the silica framework of the zeolite sodalite.
Experimental ProcedureRUB-15 crystallized from a reaction mixture with the following composition: SiO,:TMAOH:H,O = 1.00:0.75:55.52 The solution was filled in Teflon-lined autoclaves (60% filling factor) and kept in an oven at a temperature between 120 and 140 C for about four weeks. The reaction product was filtered, washed with distilled water. dried at 80 c. and subsequently identified by X-ray powder diffraction.
The new spin cluster [MnII4MnIII3(teaH)3(tea)3](ClO4)2×3MeOH realizes a
topological structure of mixed-valence manganese clusters which is especially
favorable for a high-spin ground state. The magnetic properties of the spin
cluster are studied numerically by exact diagonalization of the spin
Hamiltonian. By magnetic susceptibility two exchange constants are found:
J1/kB = − 1.28 K and J2/kB = + 4.25 K, which lead
to a S = 11 high-spin ground state. Electron spin resonance (ESR) measurements
at three frequencies 95, 190 and 285 GHz confirm the large spin of the ground
state and reveal an Ising anisotropy of the ground state which is
characterized by the spin Hamiltonian
H = α(Sz)2 + β(Sz)4 with
α/h.c. = − 0.08 cm−1 and β = − 2.1 × 10−4 cm−1. Ac-susceptibility shows thermally activated relaxation of the
magnetization for temperatures above T = 1 K with an activation energy
of ΔE/kB = − 19.5 K and a relaxation time of τ0 ≈ 10−8 s.
We report on GaSb-based 2.Xμm diode lasers with an improved waveguide design, leading to a reduced beam divergence in the fast axis of 44° full width at half maximum (FWHM), compared to 67° FWHM of a conventional broadened waveguide design. 2.3μm ridge-waveguide lasers with the improved epitaxial design showed, besides the narrow beam profile in the fast axis, an excellent slow axis beam quality [M2<1.1 up to 70mW, continuous wave (cw)]. 2.0μm broad-area lasers with the improved waveguide too, exhibit a maximum cw-output power of 1.96W.
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