Real-space imaging of the atomic-scale magnetic structure of Fe _{1+ y} Te

Abstract

Spin-polarized scanning tunneling microscopy (SP-STM) has been used extensively to study magnetic properties of nanostructures. Using SP-STM to visualize magnetic order in strongly correlated materials on an atomic scale is highly desirable, but challenging. We achieved this goal in iron tellurium (Fe(1+ y)Te), the nonsuperconducting parent compound of the iron chalcogenides, by using a STM tip with a magnetic cluster at its apex. Our images of the magnetic structure reveal that the magnetic order in the monoclinic phase is a unidirectional stripe order; in the orthorhombic phase at higher excess iron concentration (y > 0.12), a transition to a phase with coexisting magnetic orders in both directions is observed. It may be possible to generalize the technique to other high-temperature superconductor families, such as the cuprates.

Cryogenic STM in 3D vector magnetic fields realized through a rotatable insert

“…5a, Fe 1.06 Te exhibits a bi-collinear stripe magnetic order with wave vector q = (1/2, 0, 1/2). Imaging of the magnetic order of Fe 1+x Te in STM was previously reported by Enayat et al 6 When the sample is imaged with a nonmagnetic tip, the Te atoms at the topmost layer dominate the image contrast, leading to a square atomic lattice showing up in the image. However, when a magnetic tip is used, the contrast of STM images contains contributions from the magnetic order of the sample.…”

“…Methods for sample growth and preparation were described elsewhere 6 . The magnetic tip apex was prepared by picking up some excess Fe atoms from the surface of Fe 1+x Te.…”

“…To name a few, SP-STM has been employed to probe the magnetization of nanoscale cobalt islands, 2 to measure the magnetic hysteresis in FM nanostructures, 3,4 and to study spin-dependent quasi-particle interference. 5 Recently, SP-STM has also been applied to study strongly correlated electron materials, 6,7 providing further insights into the exotic phases found in these materials. 8 SP-STM operating with a vector magnet has been extensively used to map the local surface spin textures in different systems, including the chiral magnetic order that develops in a Mn monolayer formed on W(110), 9 , the "stripe-like" antiferromagnetic (AFM) order present in iron-based superconducting materials, 7 , and the Neél-type AFM order in FeSe thin-film grown on the SrTiO 3 (111) surface.…”

“…6,14,15 Our method of preparing spin polarized tips is to collect either excess Fe (FM tip) or FeTe clusters (AFM tip) from the surface of an FeTe reference sample 14 . This method is capable of producing soft magnetic tips that can be polarized by a small magnetic field (∼ 0.5 T), it can reproducibly produce spin-polarized tips of different (either FM or AFM) characters, and after tip preparation, characterization of the tip can be performed on the same sample.…”

Preparation of magnetic tips for spin-polarized scanning tunneling microscopy onFe1+yTe

“…It has provided important information both about local variations in the superconducting properties and charge ordering in strongly correlated electron materials [2][3][4] and, using magnetic tips in spin-polarized STM, it has also been shown to allow for characterization of magnetism at the atomic scale in nanostructures [5,6]. Application of spin-polarized STM to strongly correlated materials has recently been demonstrated in the nonsuperconducting parent compound of the iron chalcogenide superconductors [7], providing real space images of the magnetic structure Fe 1+δ Te. Preparing and calibrating a magnetic tip for spin-polarized STM measurements has been an important obstacle towards its application to strongly correlated electron materials.…”