7 research outputs found
Ferromagnetic resonance study of sputtered Co|Ni multilayers
We report on room temperature ferromagnetic resonance (FMR) studies of [
Co Ni]N sputtered films, where nm. Two
series of films were investigated: films with same number of CoNi bilayer
repeats (N=12), and samples in which the overall magnetic layer thickness is
kept constant at 3.6 nm (N=1.2/). The FMR measurements were conducted with a
high frequency broadband coplanar waveguide up to 50 GHz using a flip-chip
method. The resonance field and the full width at half maximum were measured as
a function of frequency for the field in-plane and field normal to the plane,
and as a function of angle to the plane for several frequencies. For both sets
of films, we find evidence for the presence of first and second order
anisotropy constants, and . The anisotropy constants are strongly
dependent on the thickness , and to a lesser extent on the total thickness
of the magnetic multilayer. The Land\'e g-factor increases with decreasing
and is practically independent of the multilayer thickness. The magnetic
damping parameter , estimated from the linear dependence of the
linewidth, , on frequency, in the field in-plane geometry,
increases with decreasing . This behaviour is attributed to an enhancement
of spin-orbit interactions with decreasing and in thinner films, to a
spin-pumping contribution to the damping.Comment: 18 pages, 13 figure
Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: influence of the surface and of the inter-particle interactions
We study the magnetic properties of spherical Co clusters with diameters
between 0.8 nm and 5.4 nm (25 to 7500$ atoms) prepared by sequential sputtering
of Co and Al2O3. The particle size distribution has been determined from the
equilibrium susceptibility and magnetization data and it is compared to
previous structural characterizations. The distribution of activation energies
was independently obtained from a scaling plot of the ac susceptibility.
Combining these two distributions we have accurately determined the effective
anisotropy constant Keff. We find that Keff is enhanced with respect to the
bulk value and that it is dominated by a strong anisotropy induced at the
surface of the clusters. Interactions between the magnetic moments of adjacent
layers are shown to increase the effective activation energy barrier for the
reversal of the magnetic moments. Finally, this reversal is shown to proceed
classically down to the lowest temperature investigated (1.8 K).Comment: 13 figures submitted to Phys. Rev.
Optical modelling and analysis of the Q and U bolometric interferometer for cosmology
International audienceRemnant radiation from the early universe, known as the Cosmic Microwave Background (CMB), has been redshifted and cooled, and today has a blackbody spectrum peaking at millimetre wavelengths. The QUBIC (Q&U Bolometric Interferometer for Cosmology) instrument is designed to map the very faint polaristion structure in the CMB. QUBIC is based on the novel concept of bolometric interferometry in conjunction with synthetic imaging. It will have a large array of input feedhorns, which creates a large number of interferometric baselines. The beam from each feedhorn is passed through an optical combiner, with an off-axis compensated Gregorian design, to allow the generation of the synthetic image. The optical-combiner will operate in two frequency bands (150 and 220 GHz with 25% and 18.2 % bandwidth respectively) while cryogenically cooled TES bolometers provide the sensitivity required at the image plane. The QUBIC Technical Demonstrator (TD), a proof of technology instrument that contains 64 input feed-horns, is currently being built and will be installed in the Alto Chorrillos region of Argentina. The plan is then for the full QUBIC instrument (400 feed-horns) to be deployed in Argentina and obtain cosmologically significant results. In this paper we will examine the output of the manufactered feed-horns in comparison to the nominal design. We will show the results of optical modelling that has been performed in anticipation of alignment and calibration of the TD in Paris, in particular testing the validity of real laboratory environments. We show the output of large calibrator sources (50 ° full width haf max Gaussian beams) and the importance of accurate mirror definitions when modelling large beams. Finally we describe the tolerance on errors of the position and orientation of mirrors in the optical combiner