Exchange anisotropy — a review

Dark optical solitons: physics and applications

While virtually absent in our diet a few hundred years ago, fructose has now become a major constituent of our modern diet. Our main sources of fructose are sucrose from beet or cane, high fructose corn syrup, fruits, and honey. Fructose has the same chemical formula as glucose (C(6)H(12)O(6)), but its metabolism differs markedly from that of glucose due to its almost complete hepatic extraction and rapid hepatic conversion into glucose, glycogen, lactate, and fat. Fructose was initially thought to be advisable for patients with diabetes due to its low glycemic index. However, chronically high consumption of fructose in rodents leads to hepatic and extrahepatic insulin resistance, obesity, type 2 diabetes mellitus, and high blood pressure. The evidence is less compelling in humans, but high fructose intake has indeed been shown to cause dyslipidemia and to impair hepatic insulin sensitivity. Hepatic de novo lipogenesis and lipotoxicity, oxidative stress, and hyperuricemia have all been proposed as mechanisms responsible for these adverse metabolic effects of fructose. Although there is compelling evidence that very high fructose intake can have deleterious metabolic effects in humans as in rodents, the role of fructose in the development of the current epidemic of metabolic disorders remains controversial. Epidemiological studies show growing evidence that consumption of sweetened beverages (containing either sucrose or a mixture of glucose and fructose) is associated with a high energy intake, increased body weight, and the occurrence of metabolic and cardiovascular disorders. There is, however, no unequivocal evidence that fructose intake at moderate doses is directly related with adverse metabolic effects. There has also been much concern that consumption of free fructose, as provided in high fructose corn syrup, may cause more adverse effects than consumption of fructose consumed with sucrose. There is, however, no direct evidence for more serious metabolic consequences of high fructose corn syrup versus sucrose consumption.

http://www.perishablepundit.com/docs/fructose-and-obesity.pdf

Metabolic Effects of Fructose and the Worldwide Increase in Obesity

Two complementary effects modify the GHz magnetization dynamics of nanoscale heterostructures of ferromagnetic and normal materials relative to those of the isolated magnetic constituents. On the one hand, a time-dependent ferromagnetic magnetization pumps a spin angular-momentum flow into adjacent materials and, on the other hand, spin angular momentum is transferred between ferromagnets by an applied bias, causing mutual torques on the magnetizations. These phenomena are manifestly nonlocal: they are governed by the entire spin-coherent region that is limited in size by spin-flip relaxation processes. This review presents recent progress in understanding the magnetization dynamics in ferromagnetic heterostructures from first principles, focusing on the role of spin pumping in layered structures. The main body of the theory is semiclassical and based on a mean-field Stoner or spin-density-functional picture, but quantum-size effects and the role of electron-electron correlations are also discussed. A growing number of experiments support the theoretical predictions. The formalism should be useful for understanding the physics and for engineering the characteristics of small devices such as magnetic random-access memory elements.

/pdf/nonlocal-magnetization-dynamics-in-ferromagnetic-jgsg3oqbe6.pdf

Nonlocal magnetization dynamics in ferromagnetic heterostructures

Ferrites—ceramic ferromagnetic materials—have been considered as highly important electronic materials for more than half a century. During this time, the characteristics of commercial ferrite materials, both soft and hard ferrites, have come to approach theoretical values. The quality of commercial ferrites has been improved through accumulated scientific knowledge and advanced technology. This article provides a comprehensive survey of the historical development of the science and technology of ferrite materials as well as applications of the ferrites. The article also offers a forecast of the future of ferrites in terms of their chemistry.

The Past, Present, and Future of Ferrites

http://www2.physics.colostate.edu/groups/WuGroup/publications/MMM_2009_Recent%20advances%20in%20processing%20and%20applications%20of%20microwave%20ferrites.pdf

Recent advances in processing and applications of microwave ferrites

Stripline (SL), vector network analyzer (VNA), and pulsed inductive microwave magnetometer (PIMM) techniques were used to measure the ferromagnetic resonance (FMR) linewidth for a series of Permalloy films with thicknesses of 50 and 100nm. The SL-FMR measurements were made for fixed frequencies from 1.5to5.5GHz. The VNA-FMR and PIMM measurements were made for fixed in-plane fields from 1.6to8kA∕m (20–100Oe). The results provide a confirmation, lacking until now, that the linewidths measured by these three methods are consistent and compatible. In the field format, the linewidths are a linear function of frequency, with a slope that corresponds to a nominal Landau-Lifshitz phenomenological damping parameter α value of 0.007 and zero frequency intercepts in the 160–320A∕m (2–4Oe) range. In the frequency format, the corresponding linewidth versus frequency response shows a weak upward curvature at the lowest measurement frequencies and a leveling off at high frequencies.

/pdf/ferromagnetic-resonance-linewidth-in-metallic-thin-films-4nmku8h46u.pdf

Ferromagnetic resonance linewidth in metallic thin films: Comparison of measurement methods | NIST

Magnetic properties of lithium ferrite microwave materials

Dark solitons of magnetostatic surface waves in magnetic films have been observed for the first time. The experiments were conducted at 5.19 GHz on 7.2 \ensuremath{\mu}m single-crystal yttrium iron garnet films. The dark solitons were excited by 15 ns wide ``off'' pulses in a high power cw microwave signal applied to the film. The characteristic soliton narrowing effect in the output pulses was observed as the input power was increased above the 0.5--1 W threshold levels. The shape of the ``dark'' pulse agrees with the \ensuremath{\Vert}tanh\ensuremath{\Vert} functional dependence predicted from theory. Direct measurements of the carrier signal showed a phase shift of close to 180\ifmmode^\circ\else\textdegree\fi{} at the center of the dark soliton, also in agreement with theory.

Microwave magnetic-envelope dark solitons in yttrium iron garnet thin films.

Measurements of the position and linewidth of the main resonance in the spin‐wave spectra of 80% Ni‐20% Fe evaporated films 150 to 3200 A thick at frequencies from 0.8 to 4.0 GHz, at room temperature and with the static magnetic field perpendicular to the film plane have been performed. The center field for resonance was independent of thickness and consistent with the Kittel resonance condition for the uniform precession. The linewidth was about 30 Oe (measured as the field separation of inflection points on the absorption curve), independent of film thickness and frequency. The linewidth data have been compared to previous data for resonance with the static field parallel to the film plane and interpreted in terms of relaxation processes for the uniform precession. In general, frequency‐swept linewidths, not field‐swept linewidths, are proportional to the relaxation rate and are the quantities which should be compared. The frequency‐swept linewidth for perpendicular resonance is equal to that obtained for parallel resonance in films thinner than 500 A. This result indicates that two‐magnon scattering between the uniform precession mode and spin‐wave states for which the exchange energy term is large (wavenumber k appreciably different from zero) does not contribute to the perpendicular resonance linewidth and is the origin of the linewidth increase with thickness for parallel resonance. It appears that scattering to states with k≈0 and exchange conductivity broadening are the most reasonable sources for the residual 30 Oe linewidth.

Carl E. Patton

Papers

Recent advances in processing and applications of microwave ferrites

Ferromagnetic resonance linewidth in metallic thin films: Comparison of measurement methods | NIST

Magnetic properties of lithium ferrite microwave materials

Microwave magnetic-envelope dark solitons in yttrium iron garnet thin films.

Linewidth and Relaxation Processes for the Main Resonance in the Spin‐Wave Spectra of Ni–Fe Alloy Films