Revealing magnetic properties of thin films utilizing polarized neutrons

Polarized neutron reflectometry (PNR) is a versatile probe for the study of the magnetic moment with depth resolution. As self-calibrating technique, it provides independently values of the magnetic moment, its direction in the film plane, and film thickness together with its scattering length density values. It is layer selective and buried layers in multilayer systems can be analyzed [1].In this contribution we will provide an overview of the possibilities of PNR as well as present the reflectometer MARIA [2]. It is a state of the art reflectometer at the constant neutron flux reactor in Garching, Germany. MARIA exhibits a high dynamic range of up to 7-8 orders of magnitude and a maximum Q (momentum transfer vector) higher than 0.25 Å$^{-1}$. With the combination of a 400 x 400 mm$^2$ position sensitive detector and a time-stable 3He polarization spin filter based on Spin-Exchange Optical Pumping (SEOP), the instrument is well equipped for investigating specular reflectivity and off-specular scattering from magnetic thin films and artificially fabricated structures like nano-dots, gratings, etc. down to the monolayer regime in full spin polarization. Furthermore, the GISANS option can be used to investigate lateral correlations in the nm range. Due to the large detector and pinhole collimation of the incident neutron beam even grazing incidence diffraction measurements are possible. All the options, like GISANS, neutron polarization and 3He polarization spin filter can be moved in and out of the neutron beam within seconds by remote controlled push button operation and do not require any realignment.Magnetic fields can be applied up to 5 T and a low temperature sample environment (down to 3 K) is offered. Thin film samples may be fabricated in a MBE system nearby (deposition materials according to the requirements of the user). For investigation of samples which are sensitive to ambient conditions a UHV transport and measurement chamber with base pressure in 10−10 mbar range is provided (transfer forth and back) [3]. Typical substrate size for investigation is 10x10 mm$^2$.Examples for PNR investigation of thin films like e.g. NiO/Fe/L10-FePt, SrCoO$_x$, Co/W(110), Fe$_4$N/LaAlO$_3$(001) are discussed. However, the MARIA reflectometer and the MBE system are user instruments. Hence we offer measurement and sample preparation time to interested users [4]. Let’s discuss your ideas![1] J. A. C. Bland and C. A. F. Vaz, Chapter 7 in J. A. C. Bland and B. Heinrich, Eds., Ultrathin Magnetic Structures III, Springer-Verlag Berlin (2005)[2] Heinz Maier-Leibnitz Zentrum. (2015). J. large-scale research facilities, 1, A8. http://dx.doi.org/10.17815/jlsrf-1-29; S. Mattauch, A. Koutsioumpas, et al., J. appl. Crystallography, 51, 646 (2018)[3] A.Syed Mohd, S.Pütter, et al., Rev. Sci. Instrum. 87, 123909(2016)[4] www.mlz-garching.de/maria;www.mlz-garching.de/mb