Large magnetostrictive susceptibility in Tb–FeCo/FeCo multilayers N H Duc, T M Danh, N A Tuan, and J Teillet Citation: Applied Physics Letters 78, 3648 (2001); doi: 10.1063/1.1354663 View online: http://dx.doi.org/10.1063/1.1354663 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/78/23?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Combining large magnetostriction and large magnetostrictive susceptibility in Tb Fe Co ∕ Y x Fe − x exchangespring-type multilayers Appl Phys Lett 85, 1565 (2004); 10.1063/1.1787156 Magnetoelastic dependence of switching field in TbFe–FeCo giant magnetostrictive spring-magnet multilayers J Appl Phys 87, 5780 (2000); 10.1063/1.372520 New Fe-based amorphous alloys with large magnetostriction and wide supercooled liquid region before crystallization J Appl Phys 85, 4491 (1999); 10.1063/1.370385 Magnetic and magneto-optical properties of TbFeCo/(Pt, Pd) multilayers optimized for short wavelength recording J Appl Phys 85, 5091 (1999); 10.1063/1.370100 Magnetic properties and microstructure of giant magnetostrictive TbFe/FeCo multilayers J Appl Phys 83, 7267 (1998); 10.1063/1.367754 This article is copyrighted as indicated in the article Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions Downloaded to IP: 128.192.114.19 On: Wed, 17 Dec 2014 19:15:37 APPLIED PHYSICS LETTERS VOLUME 78, NUMBER 23 JUNE 2001 Large magnetostrictive susceptibility in Tb–FeCoÕFeCo multilayers N H Duc,a) T M Danh, and N A Tuan Cryogenic Laboratory, Faculty of Physics, Vietnam National University, Hanoi, 334 Nguyen Trai, Thanh Xuan, Hanoi, Vietnam J Teillet GMP-UMR 6634, Universite´ de Rouen, 76821 Mont-saint-Aignan, France ͑Received November 2000; accepted for publication 18 January 2001͒ ͓Tb͑Fe0.55Co0.45͒1.5 /Fe͔n and ͓Tb͑Fe0.55Co0.45͒1.5 /͑Fe0.5Co0.5͔n multilayers were fabricated by rf-magnetron sputtering from composite targets Magnetostriction was measured using an optical deflectometer The as-deposited films showed a soft magnetic and magnetostrictive character, with a coercive field H c ϭ5 mT and a parallel magnetostrictive susceptibility ʈ ϭd ʈ /d( H) ϭ1.4ϫ10Ϫ2 TϪ1 This magnetostrictive softness was strongly improved by heat treatments: the magnetostrictive susceptibility attains the huge value of 5ϫ10Ϫ2 TϪ1 in applied field of mT The low-field dependence of the magnetostrictive susceptibility and their technical characters are described in detail © 2001 American Institute of Physics ͓DOI: 10.1063/1.1354663͔ The need for microactuator applications did stimulate the development of thin films with a large magnetostriction and a large magnetostrictive susceptibility For single-layer films, the best results were obtained for the Tb–FeCo1–5 and Sm–Fe–B6 based alloys Indeed, a large low-field magnetostrictive susceptibility, ʈ ϭd ʈ /d( H)ϭ1.8 ϫ10Ϫ2 TϪ1, was reported for annealed Tb͑Fe,Co͒1.5 films.4,5 Enhanced magnetostrictive susceptibilities have been achieved for TbFeCo/FeCo multilayers, which combine layers with a large room-temperature magnetostriction and soft magnetic layers with a high magnetization.7,8 The idea of preparing this spring-magnet type magnetostrictive multilayer is to decrease the saturation field H s ͓ ϭK/2M s ͔ by enhancing the average saturation magnetization (M s ) instead of decreasing the anisotropy constant K In addition, Ludwig and Quandt9 were recently successful in showing the possibility to control the orientation of the magnetic easy axis by magnetic annealing of the Tb0.4Fe0.6 /Fe0.5Co0.5 multilayer Detailed presentations for the field dependence of the magnetostrictive susceptibilities are still lacking in the literature In this letter, we present results of our studies on magnetostriction of ͓Tb͑Fe0.55Co0.45͒1.5 /Fe͔n and ͓Tb͑Fe0.55Co0.45͒1.5 /Fe0.5Co0.5͔n multilayers Attention is focused on the low-field magnetostrictive susceptibilities and on the working point of magnetostrictive devices The ͓ Tb͑Fe0.55Co0.45͒1.5 /Fe͔n and ͓ Tb͑Fe0.55Co0.45͒1.5 / Fe0.5Co0.5͔n multilayers with nϭ82 and 40, respectively, were prepared by rf-magnetron sputtering, with individual layer thickness t TbFeCoϭ7 nm and t Feϭ5 nm The typical power during sputtering was 400 W and the Ar pressure was 10Ϫ2 mbar Composite targets consisted of 18 segments of about 20°, of different elements ͑here Tb, Fe, Co͒ The substrates were glass microscope cover slips with a nominal thickness of 150 m Both target and sample holder were water cooled Samples were annealed at temperatures from 150 to 350 °C for h in a vacuum of 5ϫ10Ϫ4 mbar in order a͒ Electronic mail: duc@cryolab.edu.vn to relieve any stress induced during the sputtering process The x-ray diffraction ͑XRD͒ results indicated that the ͑Fe,Co͒ individual layers are crystalline, while the TbFeCo layers are amorphous After annealing, the bcc-͑Fe,Co͒ peak is weakened and broadened due to the interdiffusion of atoms between the ͑Fe,Co͒ and the TbFeCo layers The magnetostriction was measured using an optical deflectometer ͑resolution of 5ϫ10Ϫ6 rad͒, in which the bending of the substrate due to the magnetostriction in the film was measured.2,10 We measured two coefficients, ʈ and Ќ , which correspond to applied fields in the film plane, being parallel and perpendicular to the sample length, respectively For the films under investigation, the in-plane magnetostriction is almost isotropic For the single-layer TbFeCo film, at H ϭ0.7 T, the difference, ␥ ϭ ʈ ϪЌ , was found to be about 10Ϫ3 The magnetostriction of the as-deposited TbFeCo/Fe multilayer, however is half of that of the single-layer film this is consistent with the fact that the magnetostriction of Fe is negligible The parallel magnetostrictive hysteresis loops are shown in Fig for the as-deposited Tb͑Fe0.55Co0.45͒1.5 FIG Parallel magnetostrictive hysteresis loops for the as-deposited Tb͑Fe0.55Co0.45͒2 single-layer ͑1͒ and the Tb͑Fe0.55Co0.45͒1.5 /Fe multilayer ͑2͒ films Definitions of magnetostriction remanence ( r ) and the coercive field ( 0 H C ) are illustrated for the Tb͑Fe0.55Co0.45͒2 film This article is copyrighted as indicated in the article Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions Downloaded to IP: 0003-6951/2001/78(23)/3648/3/$18.00 3648 © 2001 American Institute of Physics 128.192.114.19 On: Wed, 17 Dec 2014 19:15:37 Duc et al Appl Phys Lett., Vol 78, No 23, June 2001 FIG Parallel magnetostrictive hysteresis loops for the Tb͑Fe0.55Co0.45͒1.5 /Fe ͑a͒ and the Tb͑Fe0.55Co0.45͒1.5 /͑Fe0.5Co0.5͒ ͑b͒ multilayers: curves ͑1͒ as-deposited, curves ͑2͒ annealed multilayers 3649 FIG Low-field dependence of the parallel magnetostrictive susceptibility for the Tb͑Fe0.55Co0.45͒1.5 /Fe ͑a͒ and the Tb͑Fe0.55Co0.45͒1.5 /͑Fe0.5Co0.5͒ ͑b͒ multilayers: curves ͑1͒ as-deposited, curves ͑2͒ annealed multilayers to be equal to M H C Due to this magnetostriction remanence, single layer and the Tb͑Fe0.55Co0.45͒1.5 /Fe multilayer films the possible change of the magnetostriction in ͑re͒magnetizIn the as-deposited state, the low-field magnetostrictive susing fields ͑i.e., in HϾ0), ⌬ϭ S Ϫ r , is smaller than ceptibility of the multilayer is observed to be higher than that that in demagnetizing ͑reverse͒ fields ͑i.e., in HϽ0), where of the corresponding single-layer film, an expected advan⌬ϭ s Ϫ( H C )ϭ S tage of the spring-magnet type magnetostrictive multilayers The low-field dependence of the magnetostrictive susAnnealing effects cause the saturation magnetostriction to ceptibility is presented in Figs 3͑a͒ and 3͑b͒ for the decrease, but to be developed in lower magnetic fields ͓see Tb͑Fe0.55Co0.45͒1.5 /Fe and Tb͑Fe0.55Co0.45͒1.5 /͑Fe0.5Co0.5) Figs 2͑a͒ and 2͑b͔͒ The reduction of the magnetostriction multilayers, respectively As can be seen from these figures, may be due to the interdiffusion of atoms between the layers, the field direction dependence mentioned above may not be which leads to the decrease of the rare-earth concentration so clear for the case of the as-deposited films ͓see curves in and, then, of the magnetostriction in the interface phases Figs 3͑a͒ and 3͑b͔͒, but certainly becomes rather important Indeed, analysis of magnetization data11 showed that annealfor the annealed films ͓see curves in Figs 3͑a͒ and 3͑b͔͒ ing at T A ϭ350 °C made the interface spacer to extent about For the annealed Tb͑Fe0.55Co0.45͒1.5 /Fe multilayer, ʈ shows nm more The development of the magnetostriction at low a maximum ͑of 1.3ϫ10Ϫ2 TϪ1) in low magnetizing fields fields after annealing, on the one hand, is caused by the rejust above H C The as-deposited Tb͑Fe0.55Co0.45͒1.5 / laxation of the amorphous TbFeCo phase as already ob͑Fe0.5Co0.5͒ multilayer shows even a rather small and broad served for single-layer TbFeCo films.4,5 On the other hand, it magnetostrictive susceptibility maximum ( ʈ ,maxϭ0.7 may be associated to the modification of the interfacial comϫ10Ϫ2 TϪ1 only͒ in magnetizing fields In demagnetizing position and structure This will be discussed in more detail fields, ʈ ,max reaches to a value of 5.0ϫ10Ϫ2 TϪ1, which elsewhere.11 Presently, we concentrate our attention on the strongly exceeds that of 2.0ϫ10Ϫ2 TϪ1 required for the aptechnical character of the magnetostriction and the magnetoplication in magnetostrictive devices.3,12 This magnetostricstrictive susceptibility curves tive susceptibility maximum in demagnetizing fields could Like in magnetic hysteresis loops, there is a so-called be considered as a good working point for the magnetostricmagnetostriction remanence ( r ) and a coercive field H C , tive films in microsystems where ϭ0 in the magnetostrictive hysteresis loop ͑see defiIn conclusion, annealing effects enhance the magnetoThis article is copyrighted as indicated in the article Reuse of AIP content is subject to the terms at: http://scitation.aip.org/termsconditions Downloaded to IP: nitions in Fig 1͒ Note that, experimentally, H C is observed strictive susceptibility of the TbFeCo/Fe,Co multilayers in 128.192.114.19 On: Wed, 17 Dec 2014 19:15:37 3650 Duc et al Appl Phys Lett., Vol 78, No 23, June 2001 both low magnetizing and demagnetizing ͑reverse͒ fields For applications, however, the magnetostrictive susceptibility enhancement in demagnetizing fields seems to be much more useful and effective, in particular for dynamic modes For the samples under investigation, by applying a bias magnetic field as indicated at the working point ( H dc Ϸ6 mT), a magnetostriction change ⌬Ϸ10Ϫ4 can be obtained in an ac field of the magnitude of mT This work was supported by the Vietnam National University, Hanoi within Project QG.99.08 The assistance of Nguyen Thi Ngoc Anh and Vu Nguyen Thuc in performing magnetostriction measurements is gratefully acknowledged The stay of N H Duc at the GMP, University of Rouen is supported by the Ministe`re Francaise de l’Education Nationale, de la Recherche et la Technologie E Quandt, J Alloys Compd 258, 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is subject to the terms at: http://scitation.aip.org/termsconditions Downloaded to IP: 128.192.114.19 On: Wed, 17 Dec 2014 19:15:37 ... microactuator applications did stimulate the development of thin films with a large magnetostriction and a large magnetostrictive susceptibility For single-layer films, the best results were obtained... type magnetostrictive multilayer is to decrease the saturation field H s ͓ ϭK/2M s ͔ by enhancing the average saturation magnetization (M s ) instead of decreasing the anisotropy constant K In. .. For the samples under investigation, by applying a bias magnetic field as indicated at the working point ( H dc Ϸ6 mT), a magnetostriction change ⌬Ϸ10Ϫ4 can be obtained in an ac field of the