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I nfluence of domain wall interactions on nanosecond switching in magnetic tunnel junctions

I nfluence of domain wall interactions on nanosecond switching in magnetic tunnel junctions. Mehrosh Ashraf Ghaznavi Roll # 17 mphil (2013-15). Objective.

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I nfluence of domain wall interactions on nanosecond switching in magnetic tunnel junctions

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  1. Influence of domain wall interactions on nanosecond switching in magnetic tunnel junctions Mehrosh Ashraf Ghaznavi Roll # 17 mphil(2013-15)

  2. Objective • To obtain microscopic evidence of the influence of domain wall stray field on the nano second magnetization switching in magnetic trilayer system • By Fabien Romanens, Jan Vogel, Wolfgang Kuch, Keiki Fukumoto, Julio Camarer, Stefania Pizzini. Marlio Bonfim.

  3. We will learn….. • What is magnetic tunnel junction (trilayer system)? • Magnetization switching • Influence of domain wall on switching. • Techniques to visualize the effect.

  4. What is magnetic tunnel junction? Active part of magnetic tunnel junction is consist of an ultrathin soft magnetic layer and a harder magnetic layer separated by a non magnetic spacer layer.FM layers are separated by a very thin (≤1nm) metallic non-magnetic layer, the exchange interaction is dominant.

  5. Magnetization switching Magnetization reversal, or switching, represents the process that leads to a 180° reorientation of the magnetization vector with respect to its initial direction, from one stable orientation to the opposite one. Magnetization reversal is introduced by domain wall propagation using pulsed field injection

  6. In order to induce a domain structure in the cobalt layer 3ms pulse of magnitude 10mT is used. • The stray field of the cobalt layer influence the magnetic configuration or magnetization reversal of the soft permalloy layer. • It can reduce the nucleation barrier or considerably increase the local switching speed of the soft layer.

  7. Techniques to visualize the effect • Direct evidence of the influence of domain wall stray fields in one layer on the static domain configuration of another layer has been obtained by Kuch on Co/Cu/Ni (X-PEEM) • Schafer have used Kerr microscopy to show the effect of stray fields of Bloch domain walls in a Fe whisker on the magnetization of a thin Fe film through a MgO spacer • Thomas have observed that repeated motion of domain walls in the soft magnetic layer of a FM/NM/FM magnetic trilayer can demagnetize the hard magnetic layer, even if the coercive field of the hard layer is several times larger than the field used for the reversal

  8. Here our preference • Time & layer resolved magnetic domain imaging. we will make it confirm by • Micro magnetic simulations.

  9. Bipolar magnetic pulses with amplitude of about 6mT & length of 40ns for both negative or positive pulses are were then applied parallel to the easy axis. • The domain structure in the FeNi layer is strongly correlated with the one in Co layer due to Orange-peel coupling that tends to align the magnetization in the two magnetic layer.

  10. When the field is increases the domain wall propagation in the FeNi layer takes place first. But small pulse is not sufficient to completely align the magnetization of FeNi layer above the Co domain.

  11. At the maximum of the positive pulse some newly reverse domain also become visible • At the end of the positive pulse FeNi layer is almost saturated except for some remaining white domains at left right bottom.

  12. Micro magnetic simulations In order to get a more precise idea of the influence of stray fields emitted by domain walls micro magnetic simulations are performed using a code based on a combination of the finite element method (FEM) and the boundary element method (BEM). This scheme is particularly suited to simulate magneto static interactions of ferromagnetic particles.

  13. Simulations of a domain wall in the Co layer and its influence on the FeNi magnetization, for a spacer thickness d of 30 nm. In the top left panel, the component of the magnetization along x is shown color-coded for the Co (bottom) and FeNi (top) layers, while in the top right panel the y-component is given.

  14. X-component (left) and y-component (right) of the FeNi magnetization along x, in the middle of the simulated region, for different distances d between the Co and FeNi layers Wall

  15. conclusion • Time layer resolved domain structure reveal strong co domain wall influence on the switching of the FeNi layer • Preferential nucleation always takes place above Co domain wall & simply not caused by topographic features of the sample. • Co domain wall decrease the nucleation barrier hence increase the switching speed

  16. Applications • Spin valve and magnetic tunnel junctions are used in magnetic access memory(MRAM), devices rely on the fast switching of the magnetization of the soft layer for reading or writing separate bits of information.

  17. References • Google & Wikipedia • Domain wall dynamics and interlayer interactions in magnetic trilayer systems studied by XMCD-PEEM – Springer • Domain wall interactions in magnetic trilayer systems • Magnetic Tunnel Junction Physics & Astronomy University of Nebraska • Magnetization reversal in thin films nucleation versus propagation

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