Spin-Based Microwave Nano-Oscillators - Note Special Day and Location

Spin-Based Microwave Nano-Oscillators - Note Special Day and Location
Prof. Sergei Urazhdin, Department of Physics, West Virginia University
Date and time: Mon, Feb 07, 2011 - 11:15am
Refreshments at 11:00am
Location: Goessmann 153
Category: Condensed Matter Seminar
 Spintronics is a novel approach to electronic device architecture utilizing not only electron charges, but also spins (or the associated magnetic moments) for information storage, transmission, and processing.  I will discuss one of the proposed spintronic devices, the microwave spin torque nano-oscillator (STNO) [1].  It is perhaps the world’s smallest oscillator, based on a nanomagnet consisting of only about a million atoms.  The magnetic oscillation is produced by the spin torque effect exerted on the nanomagnet by spin-polarized electrical current. The major shortcomings of STNO are large linewidth of the generated signals and small output power. Both of these issues can be solved in devices utilizing several STNOs whose oscillations are synchronized, i.e. locked in phase due to the interaction between the oscillators.  To achieve efficient synchronization, we must understand how STNO respond to external signals, and what signals they in turn produce. I will describe our measurements of the response of STNO to microwave fields, and demonstrate that they exhibit a complex pattern of fractional synchronization to those fields (Devil’s staircase) [2].  I will show that fractional synchronization is linked to the symmetry of the system, and enables one to extract information about the properties of nanoscale oscillators which are too small for the standard characterization techniques. I will also describe our measurements of the spin waves emitted by the STNO, which can by utilized as the mechanism for their synchronization [3]. Unexpectedly, the emission is strongly directional, placing strong constraints on the possible geometries of devices. I will show that the directionality can be explained by the anisotropy of the spin wave spectrum. Finally, I will use the described nano-oscillators as an example to discuss why nanoscale is important in modern science and technology. [1] Kiselev et al., Nature 425, 380 (2003). [2] Urazhdin et al., Phys. Rev. Lett. 105, 104101 (2010) [3] V.E. Demidov, S. Urazhdin, and S.O. Demokritov, Nature Mat. 9, 984 (2010).