Thickness dependence of Morin transition temperature in iridium-doped hematite layers studied through nuclear resonant s
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Thickness dependence of Morin transition temperature in iridium-doped hematite layers studied through nuclear resonant scattering Ko Mibu1 · Kazuaki Mikami1 · Masaaki Tanaka1 · Ryo Masuda2 · Yoshitaka Yoda3 · Makoto Seto2
© Springer International Publishing AG, part of Springer Nature 2017
Abstract The Morin transition of very thin Ir-doped α-Fe2 O3 films, which is not detectable with conventional magnetization measurements, was studied by conversion electron M¨ossbauer spectroscopy using a 57 Co source and nuclear resonant scattering using a synchrotron light source. It was found that (i) the Morin transition temperature increases as the Ir ratio increases, (ii) it decreases when the film thickness decreases, and (iii) the transition becomes irreversible when Ir ratio is small and the thickness is thin. These tendencies were found reproducible and systematic, although the mechanisms are to be clarified by further studies. Keywords M¨ossbauer spectroscopy · Nuclear resonant scattering · Thin films · Antiferromagnet · Magnetic anisotropy · Hematite · Morin transition
1 Introduction In magnetic recording and spintronics devices, antiferromagnetic layers are often used to pin the magnetization direction of ferromagnetic layers through the interfacial magnetic coupling. In the recent trend to use ferromagnetic layers with perpendicular magnetization for such devices, a variety of antiferromagnetic layers with perpendicular magnetic moments This article is part of the Topical Collection on Proceedings of the International Conference on the Applications of the M¨ossbauer Effect (ICAME 2017), Saint-Petersburg, Russia, 3-8 September 2017 Edited by Valentin Semenov Ko Mibu
k [email protected] 1
Graduate School of Engineering, Nagoya Institute of Technology, Nagoya, Aichi 466-8555, Japan
2
Research Reactor Institute, Kyoto University, Kumatori, Osaka 590-0494, Japan
3
Japan Synchrotron Radiation Research Institute, Sayo, Hyogo 679-5198, Japan
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are required to be developed. Antiferromagnetic hematite (α-Fe2 O3 ) layers grown with the hexagonal (0001) orientation are one candidate for such materials. The magnetic moments of pure α-Fe2 O3 align along the hexagonal c-axis at low temperatures, but turn to the cplane when the temperature becomes higher than the Morin transition temperature, which is 263 K in pure bulk samples. If the Morin transition temperature in α-Fe2 O3 (0001) films is raised above room temperature to the practical device-operation temperatures, by means of element doping or some other methods, the films become useful for device applications. Usually for bulk samples, the Morin transition can be detected from temperature dependence of magnetization [1], and also from M¨ossbauer spectra through temperature dependence of the quadrupole shift in magnetically-split sextet patterns [2, 3]. One method to increase the Morin transition temperature of α-Fe2 O3 is doping heavy metals such as iridium (Ir) to α-Fe2 O3 [4–6]. However, the Morin transition tempe
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