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We propose a spin-valve device consisting of a nonmagnetic semiconductor quantum well, sandwiched between ferromagnetic semiconductor layers that act as barriers. The total conductance through such a trilayer depends on the relative magnetization of the two ferromagnetic-barrier layers which act as “spin filters.” With respect to practical realization, EuS/PbS heterostructures may be a suitable candidate. The magnetoresistance should exceed 100% for a wide range of the thicknesses of both the quantum well and the ferromagnetic barriers. From a fundamental physics point of view, the device may not only give insight into the spin lifetimes of the nonmagnetic layer, but the strong spin accumulation taking place in the quantum well may lead to novel optical and nuclear magnetic resonance properties.

Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. A comprehensive experimental study on the antiferromagnetic interlayer exchange coupling in high quality epitaxial all-semiconducting EuS/ PbS/ EuS trilayers is reported. The influence of substrates, of the thickness of the nonmagnetic PbS spacer layer, and of temperature was investigated by means of SQUID magnetometry. In trilayers with a PbS thickness between 4 and 12 Å the low temperature hysteresis loops showed the signature of antiferromagnetic coupling. The value of the interlayer exchange coupling energy was determined by simulating the data based on a Stoner-Wohlfarth model. An important observation was that the interlayer exchange coupling energy varies strongly with temperature, consistent with a power-law dependence of the exchange coupling constant on the saturation magnetization of the EuS layers. While no theoretical description is readily available, we conjecture that the observed behavior is due to a dependence of the interlayer exchange coupling energy on the exchange splitting of the EuS bands.

We examine the role of Mn diffusion in the thermal stability of tunneling spin polarization P by directly measuring P of Al∕AlOx∕Co∕FeMn and Al∕AlOx∕Co90Fe10∕FeMn junctions using superconducting tunneling spectroscopy (STS). We confirm Mn diffusion in our junctions using x-ray photoelectron spectroscopy after an ultrahigh vacuum 500°C anneal. Surprisingly, and in contrast to the current belief, no drop in P is observed using STS. Therefore, though Mn diffuses significantly, it cannot be solely responsible for the drop in tunneling magnetoresistance observed after postdeposition anneals above 300°C.

In view of potential applications as a spin filter in spintronic devices, we systematically studied the growth by sputtering of ferromagnetic EuS barriers. The relationship between growth and magnetic and transport properties, also in combination with magnetic and nonmagnetic materials, was investigated. We demonstrate that growth at lower substrate temperatures (200°C), followed by an anneal step at elevated temperatures (430°C), leads to improved magnetic and transport properties of the barrier layer. We tentatively attribute the observed low-temperature magnetoresistance of high-resistive Al/PbS/EuS/PbS/Gd devices to spin filtering.