Lujan Neutron Scattering Center at LANSCE

Highlights

Emergent magnetism at LaAlO3/SrTiO3 interfaces: Fact or Fiction?

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  • Examined LaAlO3/SrTiO3 superlattices fabricated from groups in Spain and the Netherlands with polarized neutron reflectometry (PNR).
  • PNR is intrinsically sensitive to interfacial magnetization; bulk magnetometry is not.
  • Difference between the spin up and down neutron reflectivities normalized by their sum (spin asymmetry) is shown in the figure (symbols).
  • Anticipated spin asymmetry for magnetization (> 10G) assumed to be due to LaAlO3/SrTiO3 interfaces inferred from bulk magnetometry is not consistent with the neutron data.
  • The neutron experiment establishes an upper limit to interfacial magnetization of 1-2 G.

M. R. Fitzsimmons,1 N. Hengartner,1 S. Singh,1 M. Zhernenkov,1 J. Santamaria,2 A. Brinkman,3 M. Huijben,3 H. Molegraff,3 and Ivan K. Schuller4
1Los Alamos National Laboratory, 2Universidad Complutense-Madrid, 3University of Twente, The Netherlands, 4 University of California -San Diego

In an international collaboration between Universities and Los Alamos National Lab we investigated whether the claims of emerging magnetism at oxide interfaces is robust and persistent at LaAlO3/SrTiO3 interfaces.

Earlier reports claimed metallic conduction, superconductivity, magnetism, and coexistence of superconductivity and ferromagnetism at LaAlO3/SrTiO3 oxide interfaces with magnetization exceeding 10 G. However, the only reliable way to unravel the existence of magnetism from contamination is using a tour-de-force, polarized neutron reflectometry (PNR), which is intrinsically sensitive to interfacial magnetism and not subject to many misleading artifacts.  Neutron spin-asymmetry measurements on superlattices (see figure 1) is inconsistent with earlier claims of interfacial magnetism based on bulk or local magnetometry and establishes an upper limit smaller than 2 G for the LaAlO3/SrTiO3 interface. The clear conclusion is that the magnetism found earlier using bulk and/or local measurements is either caused by contamination or is only present in the first layer of a superlattice. These experiments illustrate the power of collaborative research, where state of the art sample growth at Universities is combined with powerful magnetic measurements available at DOE funded National Labs to unravel problems of major scientific interest and technological importance.

This work was supported by the Office of Basic Energy Science, U.S. Department of Energy, BES-DMS .

A detailed scientific description is available at M.R. Fitzsimmons, N. Hengartner, S. Singh, M. Zhernenkov, F. Y. Bruno, J. Santamaria, A. Brinkman, M. Huijben, H. Molegraaf, J. de la Venta, and Ivan K. Schuller, Phys. Rev. Lett. 107, 217201 (2011) and M. R. Fitzsimmons invited talk (T9.00001) at the 2012 APS March meeting in Boston.