Spin-torque oscillators with tilted fixed layer magnetization

One of the promising applications based on the spin transfer effect [1-3] is the Spin Torque Oscillator (STO) with signal generation at microwave frequencies related to ferromagnetic resonance. The STO may be thought of as a nanoscopic Yttrium Iron Garnet (YIG) oscillator with a similarly broad frequency range, but significant advantages such as easy on-chip integration, and current tunability instead of only field tunability. However, STOs still typically require a large, static, magnetic field for operation; removing the need for this field is currently an intensely researched topic. Three different STO designs have been attempted to address zero field operation: $i)$ the perpendicularly polarized STO [4], \textit{ii}) the wavy torque STO [5], and \textit{iii}) the vortex STO [6]. Recently we proposed the Tilted Polarizer STO (TP-STO) having a fixed layer with an out-of-plane magnetic easy-axis tilted a finite angle away from the film normal [7]. In this talk, I will review our simulation work of the TP-STO and show its potential to generate large output signal in zero field. I will present detailed structural and magnetic characterization of single layer L1$_{0}$ (111) FePt with tilted magnetic anisotropy and show how we have fabricated FePt/Cu/NiFe pseudo spin valves with magnetoresistance values of about 0.5{\%}, and as much as 5{\%} if each interface is dusted with CoFe. Finally, I will present our preliminary work on observing actual microwave signal generation in nano-contact TP-STOs and discuss their potential for applications. \\[4pt] References \\[0pt] [1] J. C. Slonczewski, J. Magn. Magn. Mater. 159, 1 (1996). \\[0pt] [2] L. Berger, Phys. Rev. B 54, 9353 (1996). \\[0pt] [3] J. A. Katine,et al., Phys. Rev. Lett. 84, 3149 (2000). \\[0pt] [4] D. Houssameddine, et al, Nat. Mater. 6, 447 (2007). \\[0pt] [5] O. Boulle, et al., Nat. Phys. 3, 492 (2007). \\[0pt] [6] V. S. Pribiag, et al., Nat. Phys. 3, 498 (2007). \\[0pt] [7] Yan Zhou, et al, Appl. Phys. Lett. 92, 262508 (2008); idem, accepted, J. Appl. Phys., (2009).