ARTICLE IN PRESS Journal of Magnetism and Magnetic Materials 272–276 (2004) 2086–2087 Structural, magnetostriction and Mossbauer studies of Fe/Tb(Fe0.55Co0.45)1.5/Fe sandwich films F Richommea,*, J Teilleta, D.T Huong Giangb, N.H Ducb b a GPM-UMR 6634, Universit!e de Rouen, BP 12, 76801 Saint-Etienne du Rouvray, France Cryogenic Laboratory, Faculty of Physics, Vietnam National University, Hanoi, 334 Nguyen Trai Road, Thanh Xuan, Hanoi, Viet Nam Abstract Sputtered {15 nm Fe/600 nm Tb(Fe0.55Co0.45)1.5/15 nm Fe} sandwich films have been investigated by X-ray diffraction, magnetostriction and Mossbauer measurements A perpendicular anisotropy is evidenced from the magnetostriction data for both as-deposited and 450 C-annealed films The Mossbauer spectra are fitted with two contributions The magnetisation of the TbFeCo layer is orientated out of the film plane, whereas that of the Fe layers tends to be in the plane The enhancement of the coercivity is attributed to the top TbFeCo/Fe interface r 2003 Published by Elsevier B.V PACS: 75.50.Vv; 57.60.Ch; 76.80.+y Keywords: Sandwich films; Mossbauer spectra; Magnetostriction; X-ray diffraction The amorphous a-TbFeCo alloys have been extensively studied because of their high magnetostriction, which is already applied in microsystems [1–4] In sandwich films, the magnetic properties are governed not only by the individual layers, but also by the interfacial quality We focus, in this paper, on the {15 nm Fe/600 nm Tb(Fe0.55Co0.45)1.5/15 nm Fe} sandwich films The films were prepared by RF-sputtering at 25 C and were annealed h at the temperature TA ¼ 450 C under a vacuum of  10À5 mbar The structure of the samples was investigated by X-ray diffraction using a cobalt anti-cathode (lCoÀKa ¼ 0:1790 nm) The conver sion electron Mossbauer spectra (CEMS) at room temperature were recorded using a conventional spectrometer equipped with a home-made helium–methane proportional counter The source was a 57Co in rhodium matrix The films were set perpendicular to the incident g-beam The spectra were fitted with a least-squares technique using histogram method relative to discrete *Corresponding author Tel.: +33-2-32-95-50-37; fax: +332-32-95-50-32 E-mail address: fabienne.richomme@univ-rouen.fr (F Richomme) 0304-8853/$ - see front matter r 2003 Published by Elsevier B.V doi:10.1016/j.jmmm.2003.12.844 distributions, constraining the line widths of each elementary spectrum to be the same Isomer shifts are given relatively to BCC-Fe at room temperature The obtained X-ray diffraction spectra are presented in Fig It indicates that the fine BCC-Fe grains are formed in the as-deposited film and almost remains in the 450 C-annealed one After depositing, the broad diffraction peak between 18 and 23 is characteristic of the amorphous TbFeCo layer After annealing, this peak is enhanced indicating a relaxation in the TbFeCo phase Such a structure was already observed by TEM bright field image for the sandwich film with the Fe-layer thickness of 10 nm [3] Parallel magnetostriction is showed in Fig While the saturation is rather difficult to reach, a huge magnetostriction of order of 10À3 is already achieved in 0.57 T This finding reflects a domination of the rotation process in the magnetisation mechanism, which is usually observed in films with perpendicular magnetic anisotropy [3] In addition, the magnetostriction exhibits also the enlargement of the hysteresis as well as the magnetic coercivity in the 450 C-annealed sample The Mossbauer spectra are presented in Fig The hyperfine field exhibits a broad distribution due to the different environments of Fe sites in the TbFeCo layer ARTICLE IN PRESS F Richomme et al / Journal of Magnetism and Magnetic Materials 272–276 (2004) 2086–2087 TbFeCo -10 1.00 Velocity (mm) 2087 + Intensity (a.u) BCC-Fe (b) 12 Em i ssion (a) 16 20 24 28 1.00 1.00 32 theta (degrees) Fig X-ray diffraction spectra for as-deposited (a) and 450 C-annealed (b) sandwich films 800 as-deposited 1.00 Fig Mossbauer spectra obtained at room temperature for as-deposited (a) and 450 C-annealed (b) sandwich films -6 λ // (10 ) 600 400 200 o 450 C-annealed -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 µoH (T) Fig Parallel magnetostriction of as-deposited and 450 Cannealed sandwich films For the as-deposited sample, the Mossbauer spectrum can be characterised by two separate contributions from the amorphous TbFeCo phase (with an average hyperfine field /Bhf S ¼ 18:5 T) and BCC-Fe (with /Bhf S ¼ 32:5 T) components Moreover, it turns out from the fit that the average angle (/bS) between the iron magnetic moments and the film normal is equal to 11 and 75 for the TbFeCo and Fe layers, respectively This means that the magnetisation of the TbFeCo layer seems to orientate perpendicular to film plane, whereas that of the Fe layers tends to be in the plane This magnetic configuration is clearly evidenced in the magnetic hysteresis loops for the Fe 30 nm/TbFeCo/ 30 nm Fe sandwich films [4] After annealing, the crystallisation, not only causes an enhancement of the /Bhf S (=19.6 T) of the TbFeCo component, but also induces the rotation of the magnetic moments towards the film plane (bTbFeCo ¼ 40 and bbccFe ¼ 75 ) As the CEMS is suitable to investigate hyperfine parameters of the iron nuclei within a depth range of about 100 nm from the film surface, the obtained results can be attributed to a change at the top TbFeCo/Fe interface Consequently, it is considered to be the reason for the above-mentioned reinforcement of the perpendicular anisotropy and the coercivity in annealed samples In order to verify these arguments, two layer Fe/TbFeCo and TbFeCo/Fe films, i.e samples with only the bottom Fe/TbFeCo or the top TbFeCo/Fe interfaces, respectively were prepared Practically, the above mentioned annealing effects are observed for the latter samples The work of N.H.D and D.T.H.G is supported by the State Program for Fundamental Researches of Vietnam, within project 420.301 References [1] E Quandt, A Ludwig, J Appl Phys 85 (1999) 6232 [2] N.H Duc, J Magn Magn Mater 212 (2002) 1411 [3] N.H Duc, D.T Huong Giang, V.N Thuc, N.T Minh Hong, N Chau, Physica B 327 (2003) 328 [4] N.H Duc, D.T Huong Giang, V.N Thuc, F Richomme, I Davoli, J Magn Magn Mater., presented in this conference ... iron magnetic moments and the film normal is equal to 11 and 75 for the TbFeCo and Fe layers, respectively This means that the magnetisation of the TbFeCo layer seems to orientate perpendicular... as-deposited (a) and 450 C-annealed (b) sandwich films 800 as-deposited 1.00 Fig Mossbauer spectra obtained at room temperature for as-deposited (a) and 450 C-annealed (b) sandwich films -6 λ... plane, whereas that of the Fe layers tends to be in the plane This magnetic configuration is clearly evidenced in the magnetic hysteresis loops for the Fe 30 nm/TbFeCo/ 30 nm Fe sandwich films [4]