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Magnetism due to and at interfaces

22/06/2018, Amphi Moyen, 14h

Subhankar Bedanta

Laboratory for Nanomagnetism and Magnetic Materials, School of Physical Sciences, National Institute of Science Education and Research (NISER), HBNI, Jatni-752050, India

Interface induced phenomenon in magnetic heterostructures viz. spin Hall effect/spin pumping, spin orbital torque, proximity induced magnetism/spinterface, interfacial Dzyaloshinskii-Moriya interaction (iDMI) leading to the formation of skyrmions etc. have been the area of the vivid research during last decade [1- 4]. Buckminsterfullerene (C60) is a potential candidate for organic spintronics due to many desirable properties viz. low spin orbit coupling, large spin diffusion length etc. [3]. We have prepared single layers of Fe and Co, and compared the magnetic properties to the bilayers of Fe/C60 and Co/C60. Finite magnetic moment was obtained in the C60 layer at the interface between both the Fe/C60 and Co/C60 layers studied by polarized neutron reflectivity measurement [5]. Magneto optic Kerr effect (MOKE) based microscopy was performed to observe the effect of the magnetic C60 layer on the hysteresis loop shape and the domain images of the Fe or Co layers [6]. Significant change between the single layer and bilayer samples were observed due to polarized charge transfer at the hybridized interface. In the second part of my talk I will present our recent work on topological insulators (TIs)/ferromagnetic (FM) heterostructures. TIs are quantum materials having insulating properties in bulk, but display gapless conducting surface states [7,8]. The spin of electron is locked to its momentum direction, which is the origin of the very high spin orbit coupling in such systems. We have investigated the spin pumping by measuring inverse spin Hall effect (ISHE) in Bi2Se3/CoFeB heterostructures using ferromagnetic resonance (FMR). A significant spin pumping has been observed. Angle dependent measurements were performed to exclude other galvanometric effects e.g. anisotropic magnetoresistance, anomalous magnetoresistance etc. [9] I would also present our recent micromagnetic simulations for the skyrmion formation in ultrathin films with various combination of perpendicular anisotropy and the iDMI. We vary the shape of the magnetic nanoelement and show the edge effect on skyrmion formation and stabilization [10].

Acknowledgements : I like to thank my collaborators Mr. A. K. Behera, Mr. S. S. Mishra, Mr. S. Mallick, Ms. Srijani Mallik, Dr. Braj Bhusan Singh, Dr. Stefan Mattauch, Dr. Syed Mohd Amir, Dr. Manas K. Dalai, Prof. Thomas Brückel, Ms. Manisha Samanta and Prof. Kanishka Biswas for their active contribution to this work. We acknowledge the financial support by various funding agencies such as DAE, DST-SERB, DST-Nanomission.

References :

[1] F. Hellman et al. Rev. Mod. Phys. 89, (2017) 025006 ;

[2] S. Sanvito, Nat. Phys. 6, (2010) 562 ;

[3] W. J. M. Naber et al., J. Phys. D : Appl. Phys. 40, (2007) R205 ;

[4] A. Fert et al. Nat. Rev. Mat. 2, (2017) 17031 ;

[5] S. Mallik et al., Sci. Rep. 8, (2018) 5515 ;

[6] S. Mallik et al., AIP Advances, 4, (2014) 097118 ;

[7] M. Z. Hasan et al. Rev. Mod. Phys. 82, (2010), 3045 ;

[8] X. L. Qi et al. Rev. Mod. Phys. 83, (2011), 1057 ;

[9] B. B. Singh et al. (manuscript under preparation) ;

[10] A. K. Behera et al. J. Phys. D- Appl. Phys. (in print).