Bulk Versus Surface Magnetic Texture in Thin Films Obtained by Pulsed Laser Deposition
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Bulk Versus Surface Magnetic Texture in Thin Films Obtained by Pulsed Laser Deposition Monica Sorescu1, A. Grabias,1,2 D. Tarabasanu-Mihaila3 and L. Diamandescu3,4 1
Duquesne University, Physics Department, Pittsburgh, PA 15282-0321, USA Institute of Electronic Materials Technology, Wolczynska 133, 01-919 Warsaw, Poland 3 Institute of Atomic Physics, R-76900 Bucharest-Magurele, Romania 4 Universita “Ca Foscari”, Dipartimento Di Chimica Fisica, Calle Larga S. Marta 2137, 30123 Venezia, Italy 2
ABSTRACT In this paper we present a direct comparison between the properties of bulk magnetic systems and those of corresponding thin films obtained by pulsed laser deposition. These are: Fe50Co50, Fe3O4, Fe3O4:Co and Fe2O3:Cr. Using transmission and conversion electron Mössbauer spectroscopy, we present results on the bulk and surface hyperfine magnetic fields, site populations and magnetic texture. Our results support an increase in the hyperfine field values at surfaces, a more pronounced out-of-plane magnetic texture in the films, as well as a perfect transfer of stoichiometry and substitution level from target to substrate materials. INTRODUCTION Pulsed laser deposition has been extensively used in obtaining thin films of ferroelectrics and superconductors [1]. Recently, it became a promising method for fabricating thin films from several classes of magnetic materials, such as metallic glasses [2]. In this regard, laser ablation deposition of iron oxides and intermetallics represents a challenging approach and was undertaken in the present study. Using transmission and conversion electron Mössbauer spectroscopy, the magnetic properties of these systems are related to those of the corresponding bulk materials. EXPERIMENTAL Pulsed laser deposition was performed with an excimer laser (Lambda Physik COMPEX 102) at a wavelength of 248 nm and a pulse width at half maxima of 8 ns. A repetition rate of 10 Hz was used between laser pulses and an energy per pulse of 450 mJ was delivered. The vacuum in the deposition chamber (Neocera) was better than 1.5x10-5 torr. About 54,000 laser pulses were necessary in order to obtain films with a thickness of 50 nm, which were characterized by standard X-ray diffraction. The CEMS spectra were measured at room temperature with a gas-flowed electron counter (helium-6% methane) using a 25 mCi 57Co-in-Rh source. The spectra of the corresponding bulk materials were measured in the conventional transmission geometry. All spectra were analyzed by least-squares fitting using the NORMOS package. J7.2.1 Downloaded from https://www.cambridge.org/core. YBP Library Services, on 20 Aug 2018 at 16:51:46, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-721-J7.2
RESULTS AND DISCUSSION Figure 1 (a) shows the transmission Mössbauer spectrum of bulk Fe50Co50 system (powder) and Figure 1 (b) presents the CEMS spectrum of the Fe50Co50 thin film obtained by laser ablation deposition on a Si (111) substrate. The magnetic hyperfine fields
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