Angular dependence of the electrically driven and detected ferromagnetic resonance in Ni36_{36}Fe64_{64} wires

We study the angular dependence of ferromagnetic resonance (FMR) in Ni$_{36}$Fe$_{64}$ wires using both traditional microwave-absorption and electrical-detection techniques. In our experiments we apply a static magnetic field at an angle $\theta$ with respect to the wire, while the microwave current, which is responsible for driving FMR, is always flowing along the wire. For different $\theta$s we find a very similar behavior for both microwave-absorption and electrically-detected FMR -- the resonance magnetic field follows a simple "$1/\cos(\theta)$" dependence. This simple behavior highlights the importance of the relative orientation between the driving current and magnetic field. We also investigated the dependence of the electrically detected FMR on dc and rf (microwave) current magnitudes. As expected, the resonance signal increases linearly with both the applied dc current and the microwave power

Anisotropic magnetoresistance in antiferromagnetic Sr2IrO4

We report point-contact measurements of anisotropic magnetoresistance (AMR) in a single crystal of antiferromagnetic (AFM) Mott insulator Sr2IrO4. The point-contact technique is used here as a local probe of magnetotransport properties on the nanoscale. The measurements at liquid nitrogen temperature revealed negative magnetoresistances (MRs) (up to 28%) for modest magnetic fields (250 mT) applied within the IrO2 a-b plane and electric currents flowing perpendicular to the plane. The angular dependence of MR shows a crossover from four-fold to two-fold symmetry in response to an increasing magnetic field with angular variations in resistance from 1-14%. We tentatively attribute the four-fold symmetry to the crystalline component of AMR and the field-induced transition to the effects of applied field on the canting of AFM-coupled moments in Sr2IrO4. The observed AMR is very large compared to the crystalline AMRs in 3d transition metal alloys/oxides (0.1-0.5%) and can be associated with the large spin-orbit interactions in this 5d oxide while the transition provides evidence of correlations between electronic transport, magnetic order and orbital states. The finding of this work opens an entirely new avenue to not only gain a new insight into physics associated with spin-orbit coupling but also better harness the power of spintronics in a more technically favorable fashion.Comment: 13 pages, 3 figure

Electrically Tunable Band Gap in Antiferromagnetic Mott Insulator Sr2IrO4

The electronic band gap in conventional semiconductor materials, such as silicon, is fixed by the material's crystal structure and chemical composition. The gap defines the material's transport and optical properties and is of great importance for performance of semiconductor devices like diodes, transistors and lasers. The ability to tune its value would allow enhanced functionality and flexibility of future electronic and optical devices. Recently, an electrically tunable band gap was realized in a 2D material - electronically gated bilayer graphene [1-3]. Here we demonstrate the realization of an electrically tunable band gap in a 3D antiferromagnetic Mott insulator Sr2IrO4. Using nano-scale contacts between a sharpened Cu tip and a single crystal of Sr2IrO4, we apply a variable external electric field up to a few MV/m and demonstrate a continuous reduction in the band gap of Sr2IrO4 by as much as 16%. We further demonstrate the feasibility of reversible resistive switching and electrically tunable anisotropic magnetoresistance,which provide evidence of correlations between electronic transport, magnetic order, and orbital states in this 5d oxide. Our findings suggest a promising path towards band gap engineering in 5d transition-metal oxides that could potentially lead to appealing technical solutions for next-generation electronic devices.Comment: 14 pages, 6 figure

Wearable nanosensor-based hardware and software complex for dynamic cardiac monitoring

To date, continuous dynamic monitoring of the cardiovascular system is relevant for improvement of the quality of diagnosis of cardiac diseases. The equipment available for continuous cardiac monitoring operates in the standard frequency range, has a low resolution, and contains filters that limit signals in low and high frequencies. The development of wearable devices and high-resolution methods for dynamic cardiac monitoring to record signals in the range from 0 to 3500 Hz without filtering and averaging is of high priority. In addition, this will allow us to obtain new data on the atria and ventricles of the heart and to detect cardiovascular diseases at an early stage. A wearable hardware and software complex based on nanosensors was developed, and preliminary technical tests of the complex were carried out. An algorithm and a program were developed to detect micropotentials over the entire duration of the ECG signal except for the waves of cardiac pulses and sharp peaks in signal processing. Histograms were built for quantitative evaluation of micropotentials, and the total energy of micropotentials was calculated. Preliminary medical studies were carried out on volunteers