Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session V7: Applications of Magnetic Thin Films with Tilted Anisotropy |
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Sponsoring Units: GMAG Chair: Johan Ã…kerman, Royal Institute of Technology, Sweden Room: 407 |
Thursday, March 19, 2009 8:00AM - 8:36AM |
V7.00001: Magnetic Thin Films for Perpendicular Recording Invited Speaker: Magnetic recording technology has shown a rapid growth over the past decade or more with the areal density growth rate more than 40\% due to introduction of giant magneto-resistive (GMR), tunneling magneto-resistive (TMR) head and perpendicular recording technology. Current products are in the range of 300- 400Gb/in$^2$ and demonstrations of 600-800Gb/in$^2$ have occurred for perpendicular recording. Recent progresses are mainly due to improvement of magnetic thin film media signal to noise ratio. In this talk, we give a brief summary of recent progresses on perpendicular recording media technology and look at possible extension for ultra high areal density recording based on recording physics and media designs. First we are going to give a brief review on the advantages of the 1st generation of perpendicular recording media as compared to longitudinal recording media. Then the effect of media switching field and switching field distribution will be discussed. We show several different media designs and show its impact to the recording technology, including media with tilted anisotropy, media with coupled granular continuous (CGC) structure, media with exchange coupled composite structure and media with exchange spring system. In addition, we will discuss the impact of media grain size on achievable areal density, the ultimate limit for magnetic recording based on continuous media. Finally, a possible extension and its impact are discussed. As stated before, here we will not try to dig into very specific detail of each topic but look at the basic concept and physics behind each topic that may potentially lead to new technology break through. [Preview Abstract] |
Thursday, March 19, 2009 8:36AM - 9:12AM |
V7.00002: Approaches and Applications of Tilted Magnetic Anisotropy in Hard Disk and STT-RAM Magnetic Recording for Extremely High Areal Density Invited Speaker: Using tilted magnetic anisotropy in magnetic recording media has been proposed and demonstrated to address several key challenges for future hard disk magnetic recording several years ago. Recent simulations show the potential benefit of using tilted magnetic anisotropy in patterned composite magnetic media that can supports the recording areal density up to several Terabit per square inch. In this talk, I will first present the fundamental physics of the advantages of using tilted magnetic anisotropy in magnetic recording media and spin torque transfer random access memory (STT RAM). Then several approaches to experimentally make magnetic films with tilted anisotropy will be presented and discussed in details. These include 1) crystallographically controlling the tilted magnetic easy axis by using proper underlayers and seedlayers; 2) physically engineering the tilted magnetic easy axis by oblique sputtering on smooth or curved substrates; 3) mechanically engineering the tilted magnetic easy axis by self --assembling magnetic nanoparticles with special shape (such as octahedral-shaped L10 phase FePt nanoparticles); 4) micromagnetically engineering the titled magnetic easy axis by exchange-coupling two magnetic layers with different magnetic easy axis and anisotropy constant. Results based on hcp phase Co-alloy and L10 phase FePt and FePd films will be presented in details. Finally, I will propose and discuss how to use tilted magnetic anisotropy for the magnetic free layer in the magnetic tunnel junction (MTJ) to reduce the critical switching current density while keeping the thermal stability, which can extend the recording density of the proposed STT RAM further. [Preview Abstract] |
Thursday, March 19, 2009 9:12AM - 9:48AM |
V7.00003: Magnetic nanocap arrays with tilted magnetization Invited Speaker: In modern magnetic recording materials the ``superparamagnetic effect'' has become increasingly important as new magnetic hard disk drive products are designed for higher storage densities. In this regard, patterned media [1], where two-dimensional arrays of nanostructures are used, is one of the concepts that might provide the required areal density in future magnetic recording devices. However, also nanostructure arrays will ultimately need high anisotropy material such as L10-FePt to provid enough thermal stability and thus much higher writing fields than currently obtainable from perpendicular magnetic recording heads. One proposed solution to this problem is the use of tilted magnetic recording media [2]. The basic idea is to tilt the easy axis of the magnetic medium from the perpendicular direction to 45 degree. In this case, the switching field will be reduced by a foctor of two in the Stoner-Wohlfarth limit. Recently, this approach was realized by oblique film deposition onto arrays of self-assembled spherical particles [3-5]. In this presentation, recent results on different film systems including Co/Pt multilayers, FePt and CoPtCr-SiO$_{2}$ alloys which have been deposited onto SiO$_{2}$ particle monolayers will be presented. It turned out that by tuning the growth conditions single domain nanocaps with enhanced magnetic coercivity and tilted anisostropy axis can be achieved even for particle sizes below 50 nm. \\[4pt] [1] B. D. Terris and T. Thomson, J. Phys. D: Appl. Phys. 38 (2005) R199 \\[0pt] [2] J.-P. Wang, Nat. Mater. 4, 191 (2005). \\[0pt] [3] M. Albrecht et al., Nat. Mater. 4, 203 (2005). \\[0pt] [4] T. Ulbrich et al., Phys. Rev. Lett. 96 (2006) 077202. \\[0pt] [5] D. Makarov et al., Appl. Phys. Lett. 93, 153112 (2008). [Preview Abstract] |
Thursday, March 19, 2009 9:48AM - 10:24AM |
V7.00004: Spin-torque oscillators with tilted fixed layer magnetization Invited Speaker: 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). [Preview Abstract] |
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