Y-89 NMR studies of MBE grown DyFe2/YFe2 multilayer films

Y-89 (spin I = 1/2) NMR studies of DyFe2/YFe2 multilayer films at 4.2 K are reported and discussed. Results are presented for a 1000 Angstrom thick film of YFe2, and a 24,000 Angstrom thick superlattice film [300 Angstrom DyFe2/300 Angstrom YFe2] x 40. For comparative purposes, measurements were also made on bulk powdered YFe2 samples. In practice, there are significant differences between the Y-89 NMR in thin film and powder form. In the MBE films the NMR frequency (45.85 +/- 0.2 MHz) is shifted down in frequency by similar to0.1 MHz, with respect to bulk (powdered) YFe2 (45.94 +/- 0.09 MHz). The origin of this shift is attributed to the expanded nature of the MBE films (similar to0.8%), relative to bulk YFe2. In addition, the NMR line width is broader in the MBE films by about a factor of two. This indicates either the presence of strain within the MBE films, and/or differing dipolar fields associated with the DyFe2/YFe2 interfaces. This feature is also confirmed by the spin-spin lattice relaxation time T-2, which is almost ten times longer in the superlattice film (T-2 = 5.1 ms), than in bulk YFe2 (T-2 = 0.6 ms). It is argued that this is due to the increased inhomogeneous line-width, which inhibits energy-conserving mutual spin-spin-flops.</p

Magnetic properties of bcc Co films

The magnetic properties of epitaxial bcc Co films of thickness 10-100 Å have been investigated using the surface magneto-optic Kerr effect (SMOKE), polarized neutron reflection (PNR), and nuclear magnetic resonance (NMR). The in-plane coercivity is found to vary strongly with thickness and a large magnetocrystalline anisotropy develops in-plane at 60 Å which is maintained in thicker films. PNR measurements on a Au-coated 100-Å bcc Co film at 300 K are consistent with a layer averaged magnetic moment per atom of 1.4 μB and a magnetization profile within 50 Å of the GaAs interface. NMR measurements on a 75-Å bcc Co film at 4.2 K yield the center frequency consistent with a moment per atom of 1.4 μB

Local Effective Hölder Exponent Estimation on the Wavelet Transform Maxima Tree

We present a robust method of estimating an effective H\"older exponent locally at an arbitrary resolution. The method is motivated by the multiplicative cascade paradigm, and implemented on the hierarchy of singularities revealed with the wavelet transform modulus maxima tree. In addition, we illustrate the possibility of the direct estimation of the scaling spectrum of the effective H\"older exponent, and we link it to the established partition functions based multifractal formalism. We motivate both the local and the global multifractal analysis by showing examples of computer generated and real life time series