Nano-magnetic Probing of Magnetite (110)
Gabriela Maris, Université Radboud, Nijm
Vendredi 28/04/2006, 11h00
Bât. 1005 P.434D, CEA-Grenoble

Spin-polarized scanning tunneling microscopy (STM) and spectroscopy (STS), which allows imaging of nanometer scale magnetism in real space, has been successfully applied to metals like Fe [1] and Mn [2]. However, there is a high interest in probing the nano-magnetism of more complex materials with high potential for spin-valve and magnetic recording applications. A unique candidate in this respect is magnetite Fe3O4 which is a ferrimagnetic stable oxide abundantly found in nature and predicted to be 100% spin-polarized [3].

We present the structure and magnetic imaging of Fe3O4 (110) thin films using STM/STS. The surface morphology consists of terraces that ripple in the [-110] direction. Atomically resolved images allow us to build a model in agreement with a bulk-truncated layer which consists of iron ions belonging to the two different magnetic sublattices (octahedral and tetrahedral). Based on this model, we explain the weak contrast between tops and valleys of ridges observed in the STS current maps acquired with paramagnetic W tips. A large contrast between tops and valleys is observed in the STS current maps acquired with antiferromaganetic MnNi tips. We attribute this enhanced contrast to the detection of the spin polarized component to the tunneling current and thus, of the two magnetic sublattices. The magnetic and structural domains correlate, in agreement with our proposed model.

 

[1] A. Kubetzka et al.: Phys. Rev. Lett. 94 087204 (2005).

[2] T. K. Yamada et al.: Phys. Rev. Lett. 90 056803 (2003).

[3] Z. Zhang and S. Satphaty: Phys. Rev. B 44 13319 (1991).

 

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