Ferromagnetic resonance study of sputtered Co|Ni multilayers

We report on room temperature ferromagnetic resonance (FMR) studies of [$t$ Co$|2t$ Ni]$\times$N sputtered films, where $0.1 \leq t \leq 0.6$ nm. Two series of films were investigated: films with same number of Co$|$Ni bilayer repeats (N=12), and samples in which the overall magnetic layer thickness is kept constant at 3.6 nm (N=1.2/$t$). 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, $K_1$ and $K_2$. The anisotropy constants are strongly dependent on the thickness $t$, and to a lesser extent on the total thickness of the magnetic multilayer. The Land\'e g-factor increases with decreasing $t$ and is practically independent of the multilayer thickness. The magnetic damping parameter $\alpha$, estimated from the linear dependence of the linewidth, $\triangle H$, on frequency, in the field in-plane geometry, increases with decreasing $t$. This behaviour is attributed to an enhancement of spin-orbit interactions with $t$ decreasing and in thinner films, to a spin-pumping contribution to the damping.Comment: 18 pages, 13 figure

Negative coercivity in epitaxially grown (110) DyFe2/YFe2 superlattices

Molecular beam epitaxial methods have been used to grow single crystal Laves phase DyFe2 /YFe2 superlattice samples with a (110) growth direction. Detailed magnetization curves have been obtained for YFe2 dominated multilayer samples [wDyFe2/4wYFe2] x16 with w = 45, 50, and 55 Å. In particular, it is shown that the formation of magnetic exchange springs in the magnetically soft YFe2 layers, can be used to engineer multilayer samples with a negative coercivity. Further, by using asymmetric field cycling procedures, we have investigated the irreversible parts of the M–B loop, associated with the switching of the DyFe2 multilayers

Candidiasis Peritoneal : prevalença i factors de risc. Estudi preliminar

Introducció: Un cultiu positiu de líquid peritoneal per a Càndida spp amb clínica associada, és diagnòstic de Candidiasis Peritoneal (CP). Objetius: L'objectiu primari és coneixer la prevalença de CP. Com objectius secundaris coneixer els possibles factors de risc. Tipus d'estudi: Prospectiu, observacional. Mètodes: S'agafa una mostra de 74 pacients amb diagnòstic de peritonitis (2007-2010). Durant la cirugía s'aspira líquid peritoneal lliure i és conrea. Resultats i conclusions: La prevalença va ser del 17.6% (46.15% C. albicans). L' afectació del tracte gastro-intestinal-superior (OR 6.554) i l'aparició de fallada cardio-vascular durant la cirugia (OR 5.827), són factors de risc per a desenvolupar-la. És estudi preliminar.Introducción: Un cultivo positivo de líquido peritoneal para Candida spp con clínica asociada, es diagnostico de Candidiasis Peritoneal (CP). Objetivos: El objetivo principal es conocer la prevalencia de CP. Como objetivos secundarios, relacionar posibles factores de riesgo. Tipo de estudio: Prospectivo, observacional Método: Se recoge una muestra de 74 pacientes diagnosticados de peritonitis (2007- 2010). Durante el acto quirúrgico se aspira líquido peritoneal libre y se cultiva. Resultados y conclusiones: La prevalencia es del 17.6% (46.15% C.albicans). La afectación del tracto gastro-intestinal-sup (OR 6.554) y la aparición de fallo cardio-vascular durante la cirugía (OR 5.827), son factores de riesgo para desarrollarla. Es un estudio preliminar

Modeling the magnetic properties of DyFe2/YFe2 superlattices

The Stoner–Wohlfarth model has proved reasonably successful in describing the coercivities of antiferromagnetically coupled DyFe2/YFe2 hard/soft superlattices in the absence of magnetic exchange springs. In particular, the coercivity rises sharply as the net magnetic moment of the superlattice approaches zero. However the situation becomes more complicated as the thickness of the YFe2 layers is increased. Two distinct "instability fields" can be identified: the bending field BB, signifying the onset of a magnetic exchange spring, and the irreversible switching field BIS associated with magnetic reversal. We have developed a computational model to address this problem. In particular, it is shown that the two instability fields in question are characterized by vanishing eigenvalues in the matrix formed by the double energy derivatives [partial-derivative]2E/[partial-derivative]thetai[partial-derivative]thetaj, where E is the total energy and thetai the angle of each individual monolayer. It is shown that the model provides a very good description of the M–Bapp loops of DyFe2/YFe2 multilayer films. In particular, the coercivity of a nearly magnetically compensated multilayer (75 ÅDyFe2/150 ÅYFe2) is much reduced below the prediction of the Stoner–Wolhfarth model, in accord with experiment

Engineering coercivity in YFe2 dominated DyFe2/YFe2 superlattice by patterning

Single crystal 400 nm thick Laves phase [20 Å DyFe2/80 Å YFe2]40 superlattice have been grown by MBE with a (110) growth direction. VSM measurements performed at room temperature with an applied field range of ±1.2×105 Oe, directed along the [001] direction, reveal a unique single-phase-liked ferrimagnetic behavior. A dominant exchange spring behavior is revealed by MOKE measurement along the [–110] direction. Furthermore, for striped arrays patterned along the [001] direction with height-to-width ratio of 0.05, a shape anisotropy of the order of 104 erg/cm3 is induced, resulting into a pronounced change of coercivity due to the comparable magnitude with intrinsic anisotropies. The results demonstrate the feasibility of engineering both single-phase-liked and exchange-spring magnet behavior in Laves phase epitaxial hard/soft superlattices by patterning