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CATEGORIES:Meetings and Conferences,Presentations
DESCRIPTION:Join the Department of Physics and Astronomy on Wednesday\, Feb
 ruary 25 in White Hall\, Room G09 for the Mohindar Singh Seehra Lecture. Ou
 r guest this year is Sara Majetich (Carnegie Mellon University)\, and her t
 alk is titled "Superparamagnetism in Nanoparticles and Magnetic Tunnel Junc
 tions."\n\n \n\nAbstract\n\nA superparamagnet is a single domain where the 
 direction of the magnetic moment changes spontaneously due to thermal fluct
 uations. Superparamagnets are preferred for most biomedical applications of
  magnetic particles\, while for magnetic data storage the grains must be ab
 ove the superparamagnetic limit. The collective behavior of superparamagnet
 s will be reviewed\, both quasi-static and dynamic. Next\, measurements of 
 superparamagnetism for single Fe3O4 nanparticles will be discussed\, where 
 the particle acts as the free layer of a magnetic tunnel junction and a con
 ductive atomic force microscopy tip is used to make electrical contact. Sin
 ce the crystallographic orientation of a spherical surfactant-coated nanopa
 rticle cannot easily be controlled\, further measurements were done on lith
 ographically fabricated nanoparticles\, mainly of CoFeB\, which is the mate
 rial most commonly used in magnetic tunnel junctions (MTJs). Magnetic field
 -tuned dynamics analagous to those for the Fe3O4 particles show greatly red
 uced noise\, and telegraphing between two levels that can be correlated to 
 an energy barrier. The dynamics can also be tuned by spin transfer torque b
 y varying the bias voltage\, or by voltage control of magnetic anisotropy .
  While CoFeB is a low anisotropy material\, if the sidewalls are oxidized\,
  there can be exchange bias effects for small diameters (≤ 40 nm). Single M
 TJ experiments show rapid (500 s) training at low fields (500 Oe)\, but sin
 ce the sidewall oxide nucleation is inhomogeneous\, each MTJ is different. 
 The last part of the talk will discuss applications of electrically control
 led superparamagnets. The simplest is a random number generator\, which req
 uires a single MTJ. Analog multiplication combines MTJs with CMOS in a way 
 that is more efficient than CMOS alone. Probabilistic logic gates are intri
 guing because of their potential for reversibility. However\, it is still v
 ery challenging to make complex structures. An alternative is to use magnet
 ostatic interactions of superparamagnetic MTJs to avoid the need for wiring
  connections\, except for the inputs and outputs to this passive neural net
 work structure. The current status and future directions are described.\n\n
  \n\nBiography\n\nSara Majetich is a Professor in the Physics Department at
  Carnegie Mellon University in Pittsburgh\, PA\, USA\, with courtesy appoin
 tments in Electrical and Computer Engineering and Materials Science and Eng
 ineering. Her research focuses on nanomagnetism. It has included studies of
  collective magnetic behavior in nanoparticle assemblies through electron m
 icroscopy and small angle neutron scattering\, and magnetoresistance measur
 ements on single nanoparticles. It also includes investigation of magnetore
 sistance and current or voltage-induced switching in small magnetic tunnel 
 junctions. She received a US NSF National Young Investigator award\, and is
  a Fellow of the IEEE and the American Physical Society\, and has authored 
 over 200 papers. She has been active in the IEEE Magnetics Society\, where 
 she has been a Distinguished Lecturer\, Education Committee Chair\, and Sec
 retary/Treasurer. She is currently the President-elect of the IEEE Magnetic
 s Society.
DTEND:20260225T202000Z
DTSTAMP:20260422T212027Z
DTSTART:20260225T193000Z
GEO:39.632955;-79.954715
LOCATION:White Hall\, G09
SEQUENCE:0
SUMMARY:P&A Seehra Lecture: Sara Majetich\, "Superparamagnetism in Nanopart
 icles and Magnetic Tunnel Junctions"
UID:tag:localist.com\,2008:EventInstance_51878249737791
URL:https://cal.wvu.edu/event/pa-seehra-lecture-sara-majetich-superparamagn
 etism-in-nanoparticles-and-magnetic-tunnel-junctions
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