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SUMMARY:THz-frequency auto-oscillator based on a bi-axial antiferromagnet 
 driven by pure spin current
DTSTART:20170522T131500
DTEND:20170522T141500
DTSTAMP:20260510T043127Z
UID:43d81cafd741b36905a6b2d1d0db9c8c9ee3046a692fdf46949bdce9
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. Andrei Slavin\, Oakland University\, USA\nAntiferromagne
 tic (AFM) materials have natural resonance frequencies in the sub-THz to 
  THz  frequency range. Thus\, it is tempting to use antiferromagnets as a
 ctive layers in THz-frequency spin-torque nano-oscillators (STNOs). Howeve
 r\, a familiar mechanism of spin-transfer torque (STT) damping compensatio
 n used in ferromagnetic (FM) STNOs [1] does not work for the AFM materials
 . In the AFM two magnetic sublattices are aligned anti-parallel to each ot
 her\, so\, when  the STT compensates damping in one of the sublattices\,
   it increases the damping in the other sublattice\, resulting in a zero 
 net effect.  At the same time\, the STT can cause a lattice instability i
 n an AFM. For example\, it has been shown in [2]\, that the STT can lead t
 o the reorientation of the order vector l in the AFM with cubic anisotropy
 .\n\nIn this work we propose a novel approach to the excitation of oscilla
 tions in AFM materials. In the framework of this approach the STT is used 
 to change the effective energy landscape of the AFM. We show theoretically
 \, that in a bi-axial AFM (such as NiO [3]) the magnetic lattice can lose 
 its stability under the action of STT\, which results in a self-sustained 
 precession of the order vector l of the AFM. We found that for NiO the low
 est threshold of the self-sustained oscillations occurs for the STT direct
 ed along the hard axis of a single crystal NiO. The threshold of generatio
 n in this case is determined by the weak easy plane anisotropy (Ha1≈ 380
  Oe in NiO) of the bi-axial AFM\, and not by the Gilbert damping of  the 
 AFM. Above the generation threshold the AFM order vector l starts to prece
 ss in the AFM easy plane with the frequency defined by the magnitude  of 
 the STT and by the Gilbert damping in the AFM\, see Fig. 2. The threshold 
 of the self-sustained oscillations for the case of the STT directed  alon
 g  the easy axis of the AFM  in several orders of magnitude higher\, tha
 n in the case when the STT is directed along the AFM hard axis.\n \n[1] A
 . Slavin and V. Tiberkevich IEEE Trans. on Magn. 45\, 1875 (2009)\n[2] E. 
 V. Gomonai and V. M. Loktev Low Temp. Phys. 34\, 198 (2008)\n[3] A.J. Siev
 ers and M. Tinkham\, Phys. Rev. 129\, 1566 (1963)\n\nBio: Andrei Slavin re
 ceived PhD degree in Physics in 1977 from the St.Petersburg Technical Univ
 ersity\, St. Petersburg\, Russia.  Dr. Slavin developed a state-of-the-ar
 t theory of spin-torque oscillators\, which has numerous applications in t
 he theory of current-driven magnetization dynamics in magnetic nanostructu
 res. His current research support includes multiple grants from the U.S. A
 rmy\, DARPA\, SRC and the National Science Foundation. This research invol
 ves international collaborations with leading scientists in many countries
 \, including Germany\, Ukraine\, France\, Italy\, and the United States. D
 r. Slavin is a frequently invited speaker at magnetism conferences around 
 the world.\n\nAndrei Slavin is Fellow of the American Physical Society\, F
 ellow of the IEEE and Distinguished Professor  and Chair of the Physics D
 epartment at the Oakland University\, Rochester\, Michigan\, USA.\n 
LOCATION:MXF 1 https://plan.epfl.ch/?room==MXF%201
STATUS:CONFIRMED
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