AVS 62nd International Symposium & Exhibition
    Magnetic Interfaces and Nanostructures Tuesday Sessions
       Session MI+SA-TuA

Paper MI+SA-TuA12
Substrate Induced Spin-state Locking of [Fe(H2B(pz)2)2(bipy)] on Au(111)

Tuesday, October 20, 2015, 6:00 pm, Room 230A

Session: Spin Currents, Spin Textures and Hybrid Magnetic Structures
Presenter: Sumit Beniwal, University of Nebraska - Lincoln
Authors: S. Beniwal, University of Nebraska - Lincoln
X. Zhang, University of Nebraska - Lincoln
S. Mu, University of Nebraska - Lincoln
A. Naim, CNRS Universite de Bordeaux, France
P. Rosa, CNRS Universite de Bordeaux, France
G. Chastanet, CNRS Universite de Bordeaux, France
J. Liu, Northeastern University
G. Sterbinsky, Brookhaven National Laboratory
D. Arena, Brookhaven National Laboratory
P.A. Dowben, University of Nebraska - Lincoln
A. Enders, University of Nebraska - Lincoln
Correspondent: Click to Email
Spin-crossover (SCO) complexes hold promise for spintronics applications as room-temperature single molecular magnets. Their signature functionality arises from a central transition metal atom, which is in a d4-d7 configuration in a (pseudo)octahedral N6 environment and can be switched between a diamagnetic low-spin (S=0) and a paramagnetic high-spin (S=2) state by external stimuli such as temperature, pressure, light and electric field. The switching of the molecular spin-state is accompanied by change of other physical and electronic properties of these complexes, such as color, magnetic susceptibility and electrical conductivity. Application in devices requires that the molecules are in contact with metal electrodes, which can significantly alter their electronic and magnetic properties. This study makes use of a comprehensive suite of surface-sensitive spectroscopy and microscopy tools to investigate the electronic properties of SCO complex [Fe(H2B(pz)2)2(bipy)] on Au(111) to identify characteristic signatures of spin-state of the molecules across thermal spin transition temperature. Variable temperature scanning tunneling microscopy, performed as a function of film thickness, revealed that ordering in the molecular layers is established as the films are cooled well below their spin transition temperature, and this ordering is maintained when the films are brought back to room temperature. Temperature and thickness dependent studies of electronic structure using X-ray photoemission (XPS), X-ray absorption spectroscopy (XAS) and inverse photoemission (IPES) on surface supported networks, reveal substrate effects on the spin state. Satellite features in core level XPS Fe 2p3/2 peaks are characteristic of the spin transition, whereas angle-resolved XPS (ARXPS) helps to separately determine the electronic structure of interfacial molecules and of molecules away from the interface. Fe L-edge X-ray absorption XAS spectra taken on ultrathin films suggest that the substrate inhibits thermally induced transitions of the molecular spin state, so that both high-spin and low-spin states are preserved far beyond the spin transition temperature of free molecules. These results demonstrate that thin films of the spin crossover complexes studied have distinctively different phase transition behavior as compared to bulk-like samples, which is evidence that interface interactions can considerably affect the molecules’ structural conformation, spin state as well as electronic properties. Understanding such interface effects can help establish conditions to control the spin state of molecules and to engineer spin state transitions.