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B Koopmans

Publications and source records attributed to B Koopmans.

14 recordsLinked to original sources
PubMed2005

Unifying ultrafast magnetization dynamics.

We present a microscopic model that successfully explains the ultrafast equilibration of magnetic order in ferromagnetic metals at a time scale tau(M) of only a few hundred femtoseconds after pulsed laser excitation. It is found that tau(M) can be directly related to the so-called Gilbert damping factor sigma that describes damping of GHz precessional motion of the magnetization vector. Independent of the spin-scattering mechanism, an appealingly simple equation relating the two key parameters via the Curie temperature T(C) is derived, tau(M) approximately c(0)h/k(B)T(C)sigma, with h and k(B) the Planck and Boltzmann constants, respectively, and the prefactor c(0) approximately 1/4). We argue that phonon-mediated spin-flip scattering may contribute significantly to the sub-ps response.

Journal Article↗
PubMed2002

All-optical probe of coherent spin waves.

A novel, all-optical method to excite and detect spin waves in magnetic materials is presented. By exploiting the temperature dependence of the magnetic anisotropy, an ultrashort laser pulse is efficiently converted in a picosecond "anisotropy field" pulse that triggers a coherent precession of the magnetization. Recording the temporal evolution of the precessing spins by a time-delayed probe-pulse provides a quantitative method to study locally the magnetic anisotropy, as well as switching and damping phenomena in micromagnetic structures. Applications to nickel and permalloy ( Ni80Fe20) films are discussed, particularly showing the possibility to explore standing spin waves in thin films.

Journal Article↗
PubMed2000

Ultrafast magneto-optics in nickel: magnetism or optics?

Several magnetic and optical processes contribute to the magneto-optical response of nickel thin films after excitation by a femtosecond laser pulse. We achieved a first complete identification by explicitly measuring the time-resolved Kerr ellipticity and rotation, as well as its temperature and magnetic field dependence in epitaxially grown (111) and (001) oriented Cu/Ni/Cu wedges. The first hundreds of femtoseconds the response is dominated by state filling effects. The true demagnetization takes approximately 0.5-1 ps. At the longer (sub-ns) time scales the spins are found to precess in their anisotropy field. Simple and transparent models are introduced to substantiate our interpretation.

Journal Article↗
PubMed1989

A 4% erythromycin and zinc combination (Zineryt) versus 2% erythromycin (Eryderm) in acne vulgaris: a randomized, double-blind comparative study.

A double-blind, randomized multi-centre study was performed to evaluate the efficacy of a 4% erythromycin and zinc combination (Zineryt) versus 2% erythromycin (Eryderm). One-hundred and twenty-two patients suffering from acne vulgaris were treated with either Zineryt lotion or 2% erythromycin lotion. Acne grading and lesion counts for comedones, papules, pustules, nodules and macules were performed at each visit at 0, 1, 2, 4, 8 and 12 weeks. Treatment with Zineryt lotion was found to be more effective than with 2% erythromycin as regards the reduction in number of the acne lesions and the severity grade of the acne.

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