Micromagnetic simulations of persistent oscillatory modes excited by spin-polarized current in nanoscale exchange-biased spin valves

We perform 3D micromagnetic simulations of current-driven magnetization dynamics in nanoscale exchange biased spin-valves that take account of (i) back action of spin-transfer torque on the pinned layer, (ii) non-linear damping and (iii) random thermal torques. Our simulations demonstrate that all these factors significantly impact the current-driven dynamics and lead to a better agreement between theoretical predictions and experimental results. In particular, we observe that, at a non-zero temperature and a sub-critical current, the magnetization dynamics exhibits nonstationary behaviour in which two independent persistent oscillatory modes are excited which compete for the angular momentum supplied by spin-polarized current. Our results show that this multi-mode behaviour can be induced by combined action of thermal and spin transfer torques.Comment: 7pages, 2 figures, submitted JAP via MMM 200

Combined frequency-amplitude nonlinear modulation: theory and applications

In this work we formulate a generalized theoretical model to describe the nonlinear dynamics observed in combined frequency-amplitude modulators whose characteristic parameters exhibit a nonlinear dependence on the input modulating signal. The derived analytical solution may give a satisfactory explanation of recent laboratory observations on magnetic spin-transfer oscillators and fully agrees with results of micromagnetic calculations. Since the theory has been developed independently of the mechanism causing the nonlinearities, it may encompass the description of modulation processes of any physical nature, a promising feature for potential applications in the field of communication systems.Comment: 8 pages, 4 figures, to be published on IEEE Transactions on Magnetic

Trans-nasal endoscopic marsupialization of a voluminous radicular cyst involving maxillary sinus and nasal cavity: A case report and a literature review on this surgical approach

The treatment of a huge cystic lesion in the upper jaw involving the respiratory cavities may result challenging. A traditional oral approach entails patient discomfort and may have negative aesthetic implications. This treatment, particularly in case of enucleation not preceded by marsupialization for volumetric reduction of the lesion, may cause irreversible damage to important anatomical structures and the collapse of the bone architecture. The purpose of this case report is to show the benefits of an endoscopic trans-nasal approach for the definitive treatment of such a clinical situation. The surgical technique aimed to remove part of the cystic wall and to open the inner compartment of the lesion to the nasal cavity after the resection of the anterior edge of the inferior turbinate and the lateral wall of the inferior nasal meatus. After a follow-up period of 18 months, without any problem or discomfort for the patient, the cyst appeared radiologically healed without the loss of any lesion-associated tooth. The bone nasal cavity, the maxillary sinus and the anterior alveolar process architecture, noticeably modified by the expansive enlargement of the cyst, resulted completely restored with a complete recover of the respiratory and oral functions

Non-linear frequency and amplitude modulation of a nano-contact spin torque oscillator

We study the current controlled modulation of a nano-contact spin torque oscillator. Three principally different cases of frequency non-linearity ($d^{2}f/dI^{2}_{dc}$ being zero, positive, and negative) are investigated. Standard non-linear frequency modulation theory is able to accurately describe the frequency shifts during modulation. However, the power of the modulated sidebands only agrees with calculations based on a recent theory of combined non-linear frequency and amplitude modulation.Comment: 4 pages, 4 figure

Analysis of Marsupialization of Mandibular Cysts in Improving the Healing of Related Bone Defects

Purpose: Marsupialization, designed to reduce the mandibular cyst volume, has continued to debated regarding its influence on the healing of the related bone cavity. The aim of the present study was to evaluate the 3-dimensional radiographic variation over time in mandibular odontogenic cystic lesions after marsupialization and assess the correlations between these variations and variables that can affect the procedure. Materials and Methods: We planned a retrospective cohort study. The predictor variables were the treatment duration, preoperative volume, patient age, histologic type, and number of preoperative residual bony walls. The outcomes variables were the postoperative volume reduction and the daily reduction rate calculated using computed tomography (CT) from before to after marsupialization using software designed for volumetric reconstruction and measurement of cyst-related bone defects. The descriptive and bivariate statistics were computerized, and the significance level was set at P =.05. Results: The sample included 15 patients (12 men and 3 women; mean age, 51.6; range, 27 to 85 years) affected by keratocysts (n = 6), dentigerous cysts (n = 6), and radicular cysts (n = 3) who had undergone marsupialization. The median duration of marsupialization was 406 days (25th to 75th percentile, 276 to 519). The mean ± standard deviation (SD) pre- and postdecompression volumes were 6,908.27 ± 2,669.058 and 2,468.13 ± 1,343.517 mm3, respectively (P < 0.001), and the mean ± SD percentage of reduction was 63.90 ± 13.12%. The volume decrease in the bone defects correlated positively with the treatment duration (P =.009) and preoperative volume (P <.001). However, no correlation was found with the other variables (P >.05) nor between the daily reduction rate and other variables (P >.05). Conclusions: Marsupialization appears useful in improving the healing of cyst-related bone defects in mandibles, especially larger defects. Further studies with a wider sample size would add more knowledge to this topic

Nanocontact spin-transfer oscillators based on perpendicular anisotropy in the free layer

Micromagnetic simulations are used to predict the behavior exhibited by spin-transfer oscillators when materials with perpendicular anisotropy are introduced in the "free" layer of nanocontact devices. Under a perpendicular-to-plane bias field, the frequency exhibits nonlinear dependence on the anisotropy field, mostly originated by the exchange-dominated propagating nature of spin-wave modes. The increase of frequency without using large bias fields makes it suitable for potential technological applications. A study of the feasibility of bias-field-free devices has been also performed deriving multiharmonic signals at gigahertz frequencies. Here, the magnetization describes a gyrotropic motion where both vortex-core polarization and rotation sense switch periodically