Frequency modulation of spin torque oscillator pairs

The current controlled modulation of nano-contact based spin torque oscillator (STO) pairs is studied in both the synchronized and non-synchronized states. The synchronized state shows a well behaved modulation and demonstrates robust mutual locking even under strong modulation. The power distribution of the modulation sidebands can be quantitatively described by assuming a single oscillator model. However, in the non-synchronized state, the modulation sidebands are not well described by the model, indicating interactions between the two individual nano-contact STOs. These findings are promising for potential applications requiring the modulation of large synchronized STO arrays

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

A Blind Signature Scheme using Biometric Feature Value

Blind signature has been one of the most charming research fields of public key cryptography through which authenticity, data integrity and non-repudiation can be verified. Our research is based on the blind signature schemes which are based on two hard problems – Integer factorization and discrete logarithm problems. Here biological information like finger prints, iris, retina DNA, tissue and other features whatever its kind which are unique to an individual are embedded into private key and generate cryptographic key which consists of private and public key in the public key cryptosystem. Since biological information is personal identification data, it should be positioned as a personal secret key for a system. In this schemes an attacker intends to reveal the private key knowing the public key, has to solve both the hard problems i.e. for the private key which is a part of the cryptographic key and the biological information incorporated in it. We have to generate a cryptographic key using biometric data which is called biometric cryptographic key and also using that key to put signature on a document. Then using the signature we have to verify the authenticity and integrity of the original message. The verification of the message ensures the security involved in the scheme due to use of complex mathematical equations like modular arithmetic and quadratic residue as well

Experimental evidence of self-localized and propagating spin wave modes in obliquely magnetized current-driven nanocontacts

Through detailed experimental studies of the angular dependence of spin wave excitations in nanocontact-based spin-torque oscillators, we demonstrate that two distinct spin wave modes can be excited, with different frequency, threshold currents and frequency tuneability. Using analytical theory and micromagnetic simulations we identify one mode as an exchange-dominated propagating spin wave, and the other as a self-localized nonlinear spin wave bullet. Wavelet-based analysis of the simulations indicates that the apparent simultaneous excitation of both modes results from rapid mode hopping induced by the Oersted field.Comment: 5 pages, 3 figure

Nonresonant microwave absorption in epitaxial La-Sr-Mn-O films and its relation to colossal magnetoresistance

We study magnetic-field-dependent nonresonant microwave absorption and dispersion in thin La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ films and show that it originates from the colossal magnetoresistance. We develop the model for magnetoresistance of a thin ferromagnetic film in oblique magnetic field. The model accounts fairly well for our experimental findings, as well as for results of other researchers. We demonstrate that nonresonant microwave absorption is a powerful technique that allows contactless measurement of magnetic properties of thin films, including magnetoresistance, anisotropy field and coercive field.Comment: 20 pages, 11 figure

Heterotrophic bacterial populations and dehydrogenase activity in fish ponds under different fertilisation practices

TThe ranges of aerobic heterotrophic bacterial populations in fish culture ponds (0.04 ha) under four manurial treatments, (1) cow manure at 10 t ha-1 yr-1; urea at 100 kg N ha-1 yr-1 and single super phosphate at 50 kg P ha-1 yr-1, (2) biogas slurry at 15 t ha-1 yr-1 and inorganic fertilisers, (3) biogas slurry at 30 t ha-1 yr-1, and (4) biogas slurry at 30 t ha-1 yr-1, with supplementary feeds assessed over a period of 15 months, were 0.28-4.44,0.30-3.86, 0.48-3.81 and 0.70-4.38 x103 ml-1 with means of 1.49,1.43,1.94 and 2.08 x103 ml-1. The sediment heterotrophic bacterial counts presented a similar pattern of variation with ranges of 1.20-6.71, 1.29-4.13, 2.04-9.92 and 2.66-11.07 x105 g-1 and mean values of 3.28, 2.62, 4.87 and 5.08 x105 g-1 in the four treatments. Water temperature and water depth were in the ranges of 20.8-30.2 °C and 0.8 to 1.8 m. The ranges of different water quality parameters were pH, D.O, NH4-N, NO2-N, NO3-N, PO4-P and dissolved organic matter were 7.4-8.5, 3.5-6.1 mg l-1, 3.25-22.66, 4.63-28.95, 10.04-48.98 mg-at N l-1, 0.03-0.54 and 2.1-9.5 mg l-1. The variations in the dehydrogenase activity of the surface sediment layers, indicative of the total bacterial activity were 0.06-0.46, 0.11-0.36, 0.19-0.87 and 0.02-0.94 mg triphenyl formazone per g sediment per day with the mean levels being 0.48, 0.41, 0.28 and 0.23 mg triphenyl formazone per g sediment per day. It is apparent that the activity was higher in treatments 3 and 4. This corroborates the observations on higher heterotrophic bacterial counts in the sediments of treatments 3 and 4, attributable to availability of processed substrate as compared to the ponds with application of raw cow manure. This also suggests better sediment-water interactions in slurry-applied ponds in comparison to traditional manuring practices

Length-weight relationship of brackish water finfish Thryssa kammalensoides Wongratana, 1983 from Chilika Lagoon, India

1308-1311The length-weight relationship (LWR) of brackish water finfish Thryssa kammalensoides Wongratana, 1983 is reported for the first time during the study. Specimens (n = 862) were caught with the help of local fisherman from Chilika lagoon, east coast of India during monsoon (September-October, 2018) and post-monsoon (November, 2018-January, 2019). The maximum total length recorded in this study is the new record for the species. The data revealed that LWR of T. kammalensoides of Chilika shows a significant LWR during monsoon (r2 = 0.872) whereas moderate (r2 = 0.470) during post-monsoon

Spin transfer torque generated magnetic droplet solitons (invited)

We present recent experimental and numerical advancements in the understanding of spin transfer torque generated magnetic droplet solitons. The experimental work focuses on nano-contact spin torque oscillators (NC-STOs) based on orthogonal (pseudo) spin valves where the Co fixed layer has an easy-plane anisotropy, and the [Co/Ni] free layer has a strong perpendicular magnetic anisotropy. The NC-STO resistance and microwave signal generation are measured simultaneously as a function of drive current and applied perpendicular magnetic field. Both exhibit dramatic transitions at a certain current dependent critical field value, where the microwave frequency drops 10 GHz, modulation sidebands appear, and the resistance exhibits a jump, while the magnetoresistance changes sign. We interpret these observations as the nucleation of a magnetic droplet soliton with a large fraction of its magnetization processing with an angle greater than 90°, i.e., around a direction opposite that of the applied field. This interpretation is corroborated by numerical simulations. When the field is further increased, we find that the droplet eventually collapses under the pressure from the Zeeman energy