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1181-DD02-03

Tunneling and anisotropic-tunneling magnetoresistance in iron nanoconstrictions fabricated by focused-ion-beam Amalio Fernández-Pacheco1,2,3, José M. De Teresa2,3, R. Córdoba1,3 and Ricardo Ibarra1,2,3 1 Instituto de Nanociencia de Aragόn, Universidad de Zaragoza, Zaragoza, 50009, Spain 2 Instituto de Ciencia de Materiales de Aragón, Universidad de Zaragoza-CSIC, Facultad de Ciencias, Zaragoza, 50009, Spain 3 Departamento de Física de la Materia Condensada, Universidad de Zaragoza, Facultad de Ciencias, Zaragoza, 50009, Spain ABSTRACT We report the magnetoresistance (MR) measurements in a nanoconstriction fabricated by focused-ion-beam (FIB) in the tunneling regime of conductance. The resistance of the contact was controlled during the fabrication process, being stable in the metallic regime, near the conductance quantum, and under high vacuum conditions. The metallic contact was deteriorated when exposed to atmosphere, resulting in a conduction mechanism by tunneling. The TMR was found to be of 3% at 24 K. The anisotropic tunneling magnetoresistance (TAMR) was around 2% for low temperatures, with a field angle dependence more abrupt than in bulk Fe. This preliminary result is promising for the application of this technique to fabricate stable ferromagnetic constrictions near the atomic regime of conductance, where high MR values are expected. INTRODUCTION The mechanism of electronic transport in constrained geometries on the nanometer scale changes dramatically in comparison with bulk, once the dimensions are reduced to less than the mean free path of electrons. In this regime, electronic transport is not diffusive anymore, but ballistic, and the conductance can become quantized (G=nG0, where G0=2e2/h is the conductance quantum) [1]. In the case of magnetic materials, high-impact results were reported in the past in atomicsize contacts, with extremely large values for MR, phenomenon coined as “ballistic MR” (BMR) [2,3]. This effect was explained by the pinning of a domain wall in the constriction, restricting the transmission of electrons. However, subsequent experiments revealed that mechanical artifacts were playing a major role for these large ratios, resulting in a huge controversy [4]. Another different finding in these structures was a large anisotropy in the MR of the contacts, whose magnitude and angular dependence were found to be very distinct from bulk materials, the so called “ballistic anisotropic MR” (BAMR) [5,6,7]. This phenomenon seems to be better established than the BMR, although critical voices claim that atomic reconfigurations in the contact, rather than an intrinsic electronic effect, could explain this behavior [8]. For a recent review in the topic see reference 9. It is therefore crucial, for the study of these effects, the fabrication of stable nanocontacts, where mechanical artifacts are avoided. Most of the work in this field has been done by techniques such as scanning tunneling microscope, mechanical break junction (MBJ) and electrochemical junctions [1,9]. New nanolithog