Seminar Series by Prof. Kannan Krishnan – 3

Department of Materials Engineering
Indian Institute of Science

is pleased to invite you to the seminar on

Magnetism, microstructure and materials characterization
by
Prof. Kannan M. Krishnan
Brahm Prakash Visiting Chair
Department of Materials Engineering
Indian Institute of Science, Bangalore
and
Department of Materials Sciences & Engineering, and Physics
University of Washington
Seattle, USA

at 3:30 p.m.
on (Date to be announced)
in the Lecture Theatre, Department of Materials Engineering.

Abstract

Magnetic materials, subtle in their manifestation, are electronically driven with their origin in the Pauli exclusion principle and the existence of electron spin. They are known for a variety of both classical and quantum-mechanical effects, arising from both short- and long-range forces, and are widely associated with “microstructure” or the morphological arrangements of magnetic moments (domains), as well as phases, grains, or individual atoms themselves. These are, in part, the reason for the richness in properties and technological applications encountered in magnetic systems. These are also, in part, why the magnetic behavior of materials is poorly understood [1].

In this talk, with a materials science structure-property-processing perspective, and drawing on our work on a wide range of materials [2] (nanoparticles [3], doped semiconducting oxides [4] and epitaxially grown metallic heterostructures [5]), I will describe their behavior at relevant length scales. Advanced characterization techniques using transmission electron microscopy (electron energy-loss spectroscopy, holography [6], energy-filtered imaging [7], atomic column-by-column z-contrast imaging) and synchrotron radiation [8] (x-ray absorption spectroscopy, x-ray magnetic circular dichroism and x-ray magnetic reflectivity [9]) are integral to these studies.

Specific topics to be addressed include:

  • Self-assembly [10], inter-particle magnetic interactions/order [11] and “memory” in magnetic nanoparticle systems
  • Defect-mediated ferromagnetism [12] in transition-metal-doped dilute magnetic semiconductors
  • Exchange-bias [13], asymmetric magnetic reversal [14] and the role of buried interfaces [15] in epitaxial heterostructures [16].

1. Kannan M. Krishnan, Fundamentals and applications of magnetic materials, Oxford University Press, 820pp, ISBN 9780199570447 (Available, Summer 2016)

2. Kannan M. Krishnan et al, Jour. Mat. Sci. 41, 793–815 (2006)

3. V. F. Puntes, Kannan M. Krishnan and P.A. Alivisatos, Science, 291, 2115-2117 (2001).

4. K. G. Roberts, M. Varela, S. Rakshev, S. Pantelides, S. J. Pennycook and Kannan M. Krishnan, Phys, Rev. B 78, 014409 (2008)

5. Wei Zhang and Kannan M. Krishnan, “Epitaxial exchange-bias systems: from fundamentals to spin-orbitronics”, Materials Science & Engineering – R: Reports (in press)

6. Y. Takeno, … Kannan M. Krishnan, Appl. Phys. Lett. 105, 183102 (2014)

7. W. Grogger, B. Schaffer, Kannan M. Krishnan and F. Hofer, Ultramicroscopy 96, 481-489 (2003).

8. G. Srajer et al, Jour. Mag. Mag. Mat. 307, 1-31 (2006)

9. Sebastian Brück et al, Phys. Rev. B 81 134414 (2010)

10. Y. Bao, M. Beerman and Kannan M. Krishnan, Jour. of Mag. Mag. Mat., 272-276, Supp1, E1367-E1368 (2004)

11. Y. Gao, Y. Bao, A. B. Pakhomov, Daisuke Shindo and Kannan M. Krishnan, Phys. Rev. Lett., 96, 137205 (2006)

12. K.A. Griffin, A.B. Pakhomov, C.M. Wang, S.M. Heald, Kannan M. Krishnan, Phys. Rev. Lett., 94, 157204 (2005)

13. W. Zhang and Kannan M. Krishnan, Jour. Micromech. & Microeng. 24, 093001 (2014)

14. P. Blomqvist, Kannan. M. Krishnan and H. Ohldag, Phys. Rev. Lett., 94, 107203 (2005)

15. S. Bruck, E. Goering, G. Schutz, X. Ji and Kannan M. Krishnan, Phys. Rev. Lett. 101, 126402 (2008)

16. This work was supported by US-Grants DOE DE-AC03-76SF00098, DoE/BES ER-45987, NSF/DMR #0203069, NSF/DMR #0322729, NSF/ECS #0224138, NSF/DMR #0315460