Spinterface studies using spin-polarised metastable emission electron spectroscopy and microscopy

Activity: Talk or presentationInvited talk


Active control of molecular spinterfaces offers a promising route to novel spin-based technologies [1], as highlighted by recent reports of interfacial magnetoresistance [2] and organic-induced ferromagnetism [3]. These studies reveal the key role that the first molecular layer plays in determining spin injection and transport behaviour, specifically the formation of spin-polarised hybrid interface states (HIS) through spin-dependent chemisorption [1]. The control of such states requires a detailed knowledge of how they form and how they change with coverage, temperature, and substrate. Previously, we have investigated such factors using the extreme surface-sensitivity associated with the technique of spin-polarised metastable de-excitation spectroscopy (SPMDS) [4]. This involves exposing the spinterface to a beam of helium atoms prepared in the long-lived 23S metastable state which has an energy of 19.82 eV, ideal for probing valence-band electronic structure. For most molecules, de-excitation of the He 23S atoms occurs through an Auger-type process in which overlap of the 1s hole of the atom with a molecular orbital or surface state liberates the excited 2s electron (see Figure). In addition to revealing the properties of native ferromagnetic surfaces, this method is ideal for probing the presence or absence of spin-polarised HIS.
We previously reported how the molecular orbitals of the first molecular layer of Alq3 adsorbed on LSMO have an induced spin polarisation with a polarity opposite to the substrate. The polarity of spin polarisation for subsequent molecular layers again switches suggesting a proximity effect that is highly localised at the spinterface but which has a secondary influence on molecular growth. In this contribution, we show how charge doping is apparently required to account for such changes and discuss the possible origins of this charge. A charge-doping enhanced proximity effect has significant implications for the development of molecular spintronic devices and potentially offers a means to controlling spinterface behaviour. Additionally, we present the first results from the development of spin-polarised metastable emission electron microscopy (SPMEEM), the microscopic equivalent of SPMDS. In the same way that photoemission electron microscopy (PEEM) greatly enhances photoelectron spectroscopy, SPMEEM has the potential to extend SPMDS and spatially map the spin-polarisation of spinterfaces. We show a strong coverage dependence in the spin polarisation of the aromatic molecule naphthalene on Fe3O4, possibly arising due to a change in molecular orientation. Higher coverages form well-ordered molecular layers with a spin polarisation that is uniform across a much larger region than for the underlying substrate.

[1] M. Cinchetti, V. A. Dediu, and L. E. Hueso, Nature Mater. 2017, 16, 507
[2] K. V. Raman, A. M. Kamerbeek, A. Mukerjee et al., Nature 2013, 493, 509
[3] F. A. Ma’Mari, T. Moorsom, G. Teobaldi et al., Nature 2015, 524, 69
[4] Z. Y. Li, M. Jibran, X. Sun, et al., Phys. Chem. Chem. Phys. 2018, 20, 15871
Period25 Oct 2018
Event title2nd European Conference on Molecular Spintronics: Workshop on Spins and Interfaces
Event typeConference
LocationPeniscola, SpainShow on map
Degree of RecognitionInternational