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Lecture Sylvia Matzen


10 June 2011 FWN-Building 5114.0004 , Nijenborgh 4, 9747 AG, Groningen
Speaker: Dr. Sylvia Matzen
Affiliation: CEA-Saclay, DSM/IRAMIS/SPCSI, Gif-sur-Yvette, France
Title: Epitaxial ferrite magnetic tunnel barriers for room temperature spin filtering
Date: Fri Jun 10, 2011
Start: 11.00
Location: FWN-Building 5114.0004
Host: Beatriz Noheda
Telephone: +31 50 363 4565


T he generation of highly spin-polarized electron currents at room temperature is the basis of most spin-based device technologies. One approach known as spin filtering, has the potential of generating 100% spin-polarized currents by the spin selective transport of electrons across a ferromagnetic tunnel barrier [1]. While efficient spin filtering at room temperature is highly attractive for applications, the selection of materials having the necessary magnetic and electronic properties is quite limited. Cobalt, nickel and manganese ferrites (CoFe2O4 [2], NiFe2O4 [3], MnFe2O4) are promising candidates because they are ferrimagnetic insulators with remarkably high Curie temperatures (793 K, 850 K and 573 K respectively).

In this work, we investigate the spin-polarized tunneling characteristics of MnFe2O4(111) and CoFe2O4(111) ultrathin films. Tunnel junctions containing epitaxial ferrite tunnel barriers have been grown by oxygen plasma-assisted molecular beam epitaxy (MBE). Their structural, chemical, magnetic and electrical properties have been optimized by using a number of in situ and ex situ characterization techniques (RHEED, XPS, HRTEM, XMCD, VSM, CT-AFM). Following this optimization, we focus on their spin-polarized tunneling characteristics using two different techniques: measuring tunneling magnetoresistance and directly using the Meservey-Tedrow method. The spin-polarized transport measurements reveal the spin filtering capability of both Mn Fe2O4 and CoFe2O4 barriers, as well as the predominant effect of defects on their spin filtering efficiency.

As magnetism of thin layers is known to be affected by the decrease of thickness, it is challenging to keep the required good magnetic properties for tunnel barriers in order to achieve high spin filtering efficiency. In this talk, a comparative study of CoFe2O4(001) ultrathin films grown on different substrates will highlight the significant role of strain to tailor the magnetic properties of oxide ultrathin films, allowing for restoration of bulk magnetic properties at tunnel barrier thicknesses.

 [1]J. S. Moodera, T. S. Santos and T. Nagahama, J. Phys. Cond. Mat. 19, 165202 (2007). 

[2] A.V. Ramos, M.-J. Guittet, J.-B. Moussy, R. Mattana, C. Deranlot, F. Petroff and C. Gatel, Appl. Phys. Lett. 91, 122107 (2007).

[3] U. Lüders, M. Bibes, K. Bouzehouane, E. Jacquet, J.-P. Contour, S. Fusil, J. Fontcuberta, A. Barthélémy, and A. Fert, Appl. Phys. Lett. 88, 082505 (2006).

Last modified:22 October 2012 2.30 p.m.