Influence of field-like torque in synchronization of spin torque oscillators

The magnetization dynamics of two parallelly coupled spin torque oscillators, destabilization of steady states and removal of multistability, are investigated by taking into account the influence of field-like torque. It is shown that the existence of such torque can cancel the effect of damping and can, therefore, cause the oscillators to exhibit synchronized oscillations in response to direct current. Further, our results show that the presence of field-like torque enhances the power and Q-factor of the synchronized oscillations. The validity of the above results is confirmed by numerical and analytical studies based on the stochastic Landau-Lifshitz-Gilbert-Slonczewski equation.Comment: 10 pages, 10 figures, Accepted for Publication in IEEE Transactions on Magnetic

High Power, Continuous-wave Supercontinuum Generation in Highly Nonlinear Fibers Pumped with High Order, Cascaded Raman Fiber Amplifiers

A novel method for efficient generation of high power, equalized continuous-wave supercontinuum source in an all conventional silica fiber architecture is demonstrated. Highly nonlinear fiber (HNLF) is pumped in its anomalous dispersion region using a novel, high power, L-band laser. The L-band laser encompasses a 6th order cascaded Raman amplifier which is pumped with a high power Ytterbium doped fiber laser and amplifies a low-power, tunable L-band seed source. The supercontinuum generated 35W of power with ~40% efficiency. The Supercontinuum spectrum was measured to have a high degree of flatness of better than 5 dB over 400 nm of bandwidth (1.3 - 1.7 micron, limited by spectrum analyzer range) and a power spectral density in this region of >50 mW/nm. The extent of the SC spectrum is estimated to be upto 2 micronComment: 6 pages, 5 figure

High frequency oscillations in spin-torque nano oscillator due to bilinear coupling

Exchange coupling in an interfacial context is crucial for spin-torque nano oscillator (STNO) that consists of a non-magnetic spacer which is alloyed with a ferromagnetic material. Currently, investigations on the dynamics of the free layer magnetization and frequency enhancement in the STNO with bilinear coupling are still being actively pursued. In the present work, we investigate the dynamics of the STNO in the presence of bilinear coupling but in the absence of an external magnetic field by analyzing the associated Landau-Lifshitz-Gilbert-Sloncewski(LLGS) equation, and consequently the impact of the bilinear coupling on the dynamics of the magnetization of the free layer is studied. It is observed that the frequency of the oscillations in the magnetization component along the direction of the pinned layer polarization can be enhanced above 300 GHz by positive bilinear coupling and up to around 30 GHz by negative bilinear coupling. We further reveal a transition from in-plane to out-of-plane precession both for positive and negative bi-linear couplings. We also analyze the switching of the magnetization for different values of current and bilinear coupling. Our detailed investigations of STNO with bilinear coupling aim at the possibilities of high-frequency devices by considering the applied current and bilinear coupling in the absence of a magnetic field.Comment: 10 pages, 9 figures, Accepted for publication in Phys. Rev.

Comparison of Frictional Resistance to Sliding on Pre-Adjusted Edgewise Brackets using Three Different Methods of Ligation and the Effect of Fluoride Mouth Rinse on Friction - An Invitro Study.

Background: Friction has an important role in clinical orthodontics. The friction occurring between archwire and bracket during sliding can considerably reduce the rate of intended tooth movement and produce undesirable movement of the anchor teeth. Two factors determine the amount of friction during sliding mechanics are the coefficient of friction between contacting surfaces and the forces applied between those surfaces. The coefficient of friction is mainly determined by wire roughness, texture, or hardness of the surface which will get altered in complex oral environment. The force applied between bracket and arch wire is determined by the force exerted by the ligation. The present study focused to evaluate the effect of three methods of ligation and to find out the role of fluoride mouth rinse on friction . Aim: To compare the frictional resistance to sliding on pre adjusted edge wise brackets using three different methods of ligation and the effect of fluoride application on friction. Methods: 90 custom made bracket mounting templates were divided into three ligation groups - elastomeric modules, stainless steel ligatures and super slick. Each group consisted of 30 samples. Tests were conducted in three environmental conditions namely dry, wet by immersed in artificial saliva and after fluoride mouth rinse application. Testings were conducted on Precision Universal Tester using 5N of tensile force to pull the archwire through the bracket slot at a crosshead speed of 20 mm/min through a distance of 5 mm. The force required to initiate the sliding (static friction), which is represented by a peak in the beginning of digital readout was recorded. Results: Super slick ligation demonstrated significantly lower friction than other two groups (p<0.05) in all the three environmental conditions. When each ligation was tested under three conditions, friction significantly increased after fluoride application (p<0.05). Conclusion: Low friction ligatures like super slick can be used as an effective means to reduce friction. Prophylactic agents containing fluoride can have a deleterious effect on sliding as it is increasing the friction due to its ability to change the surface morphology at the sliding interface