Bulletin of the American Physical Society
2011 Annual Meeting of the Four Corners Section of the APS
Volume 56, Number 11
Friday–Saturday, October 21–22, 2011; Tuscon, Arizona
Session K3: Magnetic Systems |
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Chair: Shufeng Zhang, University of Arizona Room: UA Student Union Agave |
Saturday, October 22, 2011 8:30AM - 8:42AM |
K3.00001: Multiferroic Effects in W-type Hexagonal Ferrites Yiyan Sun, Young-Yeal Song, Zihui Wang, Daryl Freeman, Mingzhong Wu One major advance in the field of multiferroics in recent years is the discovery of multiferroic effects in hexagonal ferrites. The crystal structures of hexagonal ferrites can be described as the superposition of certain fundamental blocks, each containing several close-packed layers stacked in a specific sequence. Based on the way how different blocks are stacked to form a unit cell, one can classify hexagonal ferrites into six main types: M, W, Y, Z, X, and U. Within these six types, M-, Y-, Z-, and U-type hexagonal ferrites have proved to be multiferroic. This presentation reports for the first time multiferroic effects in W-type hexagonal ferrites. The sample was a 150 $\mu $m-thick Co$_{2}$W hexagonal ferrite slab cut from a single-crystal bulk. X-ray diffraction measurements confirmed the crystal structure and indicated that the hexagonal $c$ axis was along the slab normal. Static magnetic measurements indicated that the slab plane was an easy plane, and the saturation induction was 4300 G. The ferroelectric nature was confirmed by hysteresis behavior in dielectric constant vs. electric field measurements. The magneto-electric coupling manifests itself as two distinct effects: (1) a change in dielectric constant with a magnetic field applied in the easy plane, and (2) a shift in the ferromagnetic resonance field with the bias voltage applied across the slab. [Preview Abstract] |
Saturday, October 22, 2011 8:42AM - 8:54AM |
K3.00002: Damping Constant in Perpendicular Recording Media Lei Lu, Michael Kabatek, Mingzhong Wu Understanding the damping of magnetization precession in real magnetic recording media is of both fundamental and practical importance. In practical terms, the relaxation processes in media not only set a natural limit to recording data rates, but also play a critical role in microwave-assisted switching. This presentation reports on the damping in a commercial-like perpendicular media disk. The sample consists of a granular media layer and a soft capping layer and shows a coercivity of 5.2 kOe and a squareness of 0.97. The damping constant was determined through temperature- and frequency-dependent ferromagnetic resonance (FMR) measurements. The temperature-dependent FMR measurements were carried out with a 9.48 GHz cavity and magnetic fields oriented in a direction opposite to the remanent magnetization in the film. The temperature range was 110-320 K. The linewidth-temperature data were fitted with three models, the spin-flip magnon-electron scattering model, the breathing Fermi surface model, and inhomogeneity-associated line broadening. The fitting yields a $\alpha $ range of 0.07-0.15. The frequency-dependent FMR measurements were performed with a co-planar waveguide over a frequency range of 27.5-49.5 GHz. A linear fit to the linewidth-frequency data indicates a $\alpha $ value which is within the range determined from the temperature-dependent measurements. [Preview Abstract] |
Saturday, October 22, 2011 8:54AM - 9:06AM |
K3.00003: Micromagnetic simulations of antivortex formation Martin Asmat-Uceda, Kristen Buchanan Magnetic vortices are fundamental magnetic structures that form in patterned ferromagnetic materials. The study of magnetic vortices is an active field of research at present, in part because of the potential for new technologies. In addition to vortices, so called antivortex states have been found in some particular geometries such as four connected rings and cross-like nanomagnets. Antivortices may be useful for nonvolatile data storage applications, and they are also expected to show unusual transport properties in an applied magnetic field, for example, a ``topological'' Hall effect. In order to make use of magnetic antivortices, it is important to first understand how to stabilize systems that contain only a single antivortex. Micromagnetic calculations have been performed with OOMMF and LLG software to explore how the geometry of the structure affects the formation and stability of the antivortex state and whether the field history can be used to reliably select the state. [Preview Abstract] |
Saturday, October 22, 2011 9:06AM - 9:18AM |
K3.00004: Combining symmetry-mode analysis and magnetic symmetry to characterize a magnetic structure Eric Gibbs, Branton Campbell, Juan Lopes Group-theoretical symmetry-mode analysis has recently been demonstrated as an effective means of determining complicated displacive distortions of a known parent structure without any assumptions about crystallographic symmetry. After detecting the primary symmetry modes, it then proved advantageous to employ crystallographic symmetry to further constrain the subtle secondary parameters of the model. We employ an analogous combination of magnetic symmetry-modes and magnetic Shubnikov symmetry to characterize magnetic structures. [Preview Abstract] |
Saturday, October 22, 2011 9:18AM - 9:30AM |
K3.00005: Electric field control of interface magnetic anisotropy Lei Xu, Shufeng Zhang The interface magnetic anisotropy of ferromagnetic metals comes from the spin-orbit interaction. But unlike the semiconductor heterostructures, the strong electron screening would make the Rashba spin-orbit coupling (RSOC) localized within the election screening length at metallic interface. Now by explicitly taking into account the interaction between the symmetry-broken interface potential and the spin-dependent electric dipoles of the Bloch states, we find that this interaction may generate a RSOC, which is much stronger than the direct Pauli spin-orbit coupling. Due to the presence of the RSOC, the spin up and down states of the ferromagnet are spin mixed at the interface. Among other consequences, the RSOC induces a perpendicular surface magnetic anisotropy whose magnitude is comparable to the observed values in transition metals. When we apply an external electric field across the interface, the induced screening potential modifies the RSOC and thus the perpendicular anisotropy can be manipulated. [Preview Abstract] |
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