Yevgen Pogoryelov

Nonlinear frequency and amplitude modulation of a nanocontact-based spin-torque oscillator

We study the current-controlled modulation of a nanocontact spin-torque oscillator. Three principally different cases of frequency nonlinearity (d(2)f/dI(dc)(2) being zero, positive, and negative) ...

Frequency modulation of spin torque oscillator pairs

The current controlled modulation of nanocontact based spin torque oscillator (STO) pairs is studied in both the synchronized and nonsynchronized 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 nonsynchronized state, the modulation sidebands are not well described by the model, indicating interactions between the two individual nanocontact STOs. These findings are promising for potential applications requiring the modulation of large synchronized STO arrays.

Spin-torque oscillator linewidth narrowing under current modulation

We study the behavior of the linewidth of a nanocontact based spin torque oscillator (STO) under application of a radio frequency (100 MHz) modulating current. We achieve a significant (up to 85%) reduction in the STO linewidth when it is modulated across a region of high nonlinearity. The mechanism responsible for the linewidth reduction is the nonlinear frequency shift under the influence of current modulation, which reduces the nonlinear amplification of the linewidth. The reduction in the linewidth during modulation can be quantitatively calculated from the free-running behavior of the STO.

Recent Advances in Nanocontact Spin-Torque Oscillators

We present a comprehensive review of the most recent advances in nanocontact spin torque oscillators (NC-STOs). NC-STOs are highly tunable, with both applied magnetic field and dc, broadband microwave signal generators. As opposed to the nanopillar geometry, where the lateral cross section of the entire device has been confined to a typically <;100 nm diameter, in NC-STOs, it is only the current injection site that has been laterally confined on top of an extended magnetic film stack. Three distinct material combinations will be discussed: 1) a Co/Cu/NiFe pseudospin valve (PSV) where both the Co and NiFe have a dominant in-plane anisotropy; 2) a Co/Cu/[Co/Ni]4 orthogonal PSV where the Co/Ni multilayer has a strong perpendicular anisotropy; and 3) a single NiFe layer with asymmetric non-magnetic Cu leads. We explore the rich and diverse magnetodynamic modes that can be generated in these three distinct sample geometries.

Hysteretic Synchronization in Spin-Torque Nanocontact Oscillators: A Micromagnetic Study

Several experiments report the presence of finite jumps in the properties of spin-torque oscillators at room temperature, such as oscillation frequency and power as functions of current or field. On the basis of micromagnetic simulations, this paper links those experimental discontinuities to the changes in the curve slope numerically observed in the absence of thermal effects. Our numerical results show the key ingredient triggering this behavior is the presence of abrupt changes in the oscillation axis of the magnetization precession. We also predict that by fixing the bias point of the oscillator near those critical regions, it is possible to observe hysteretic synchronization. This result should be a key point in the design of nanoscale on-chip phase-locked loop receivers with improved sensitivity.

Exponentially decaying magnetic coupling in sputtered thin film FeNi/Cu/FeCo trilayers

Magnetic coupling in trilayer films of FeNi/Cu/FeCo deposited on Si/SiO2 substrates have been studied. While the thicknesses of the FeNi and FeCo layers were kept constant at 100 angstrom, the thic ...

Modulation of single and double spin torque oscillators

We discuss modulation of metallic spin torque oscillators (STOs) based on single and double nano‐contacts. The modulation behavior of both types of devices is characterized by equally spaced multiple sidebands, which can be ascribed mostly to a frequency modulation phenomenon. However, quantitative examination reveals that amplitude modulation is also present in both types of devices. We also show the feasibility of modulating the synchronized state of a double nano‐contact STO. The synchronized state can be treated as a single oscillator, which is a very promising feature for future applications of STO arrays.z

Combined Wide-Narrow Double Modulation of Spin-Torque Oscillators for Improved Linewidth During Communication

Spin-torque oscillators (STOs) offer the advantage of high modulation rates. However the existence of regions with high-frequency nonlinearity, accompanied by increased signal linewidth, limits both the usable STO frequency range and the minimum frequency of modulation. On the other hand, use of a large modulation frequency increases the frequency modulation (FM) bandwidth. In order to overcome these problems, we propose to simultaneously modulate the STO with two signals having different frequencies. We use a high-frequency, “wide” (fW=500 MHz), modulation signal to improve the STO linewidth. At the same time we use a low-frequency, “narrow” (fN=40 MHz), modulation signal to show successful narrow bandwidth modulation of the improved STO signal. The proposed method of combined wide-narrow double modulation can significantly improve the usable operating frequency range of the STOs for communication applications.

Magnetic coupling in asymmetric FeCoV/Ru/FeNi trilayers

We have investigated the magnetic anisotropy and interlayer coupling in trilayer films of permendur(100 \AA)/Ru/permalloy(100 \AA), with the thickness of the Ru spacer varying from 0 to 200 \AA. Wh ...

Manifestation of spin-Hall effect in multilayered M/N/M film structures

In the present work spin-Hall effect was for the first time experimentally utilized at room temperatures for studies of interlayer exchange coupling in ultrathin (3-40A) M/N/M film structures at zero applied external magnetic field. Application of special technique allowed to discover the possible influence of external magnetic field on the behavior of exchange coupling oscillations. Obtained results are well explained if to take into account in the RKKY model the probable influence of magnetic field on the spin-dependent reflection coefficients of spin-polarized conduction electrons from magnetic interfaces.