DSpace at VNU: Magnetisation and magnetostriction in Fe Terfecohan Fe sandwich films withan extended domain wall formation

ARTICLE IN PRESS Journal of Magnetism and Magnetic Materials 272–276 (2004) e1597–e1599 Magnetisation and magnetostriction in Fe/Terfecohan/Fe sandwich films with an extended domain wall formation N.H Duca,*, D.T Huong Gianga, V.N Thuca, I Davolib, F Richommec a Cryogenic Laboratory, Faculty of Physics, Vietnam National University, 334 Nguyen Trai Road, Thanh Xuan, Hanoi, Viet Nam b INFM e Dipartimento di Fisica, Universita" di Roma ‘‘Tor Vergata’’, via della Ricerca Scientifica 1, Roma 00133, Italy c GPM-UMR 6634, Universite! de Rouen, 76801 Saint-Etienne du Rouvray, France Abstract A magnetisation reversal associated to the formation of the so-called extended domain wall is investigated by means of magnetisation and magnetostriction measurements for the sputtered Fe/Tb(Fe0.55Co0.45)1.5/Fe sandwich films with an individual TbFeCo-layer thickness of about 600 nm and Fe-layer thickness tFe ¼ 30 and 60 nm The obtained results are attributed to the contribution of the TbFeCo core as well as the interfacial domain wall For comparison, magnetostriction data of {19 nm Terfecohan/11 nm Fe} multilayer is discussed r 2003 Elsevier B.V All rights reserved PACS: 75.60.Jk; 75.70.Ak; 75.80.+q Keywords: Magnetization process; Magnetostriction; Domain wall; Sandwich films Giant low-field magnetostriction has been extensively studied in amorphous Tb(Fe0.55Co0.45)1.5 (denoted as aTerfecohan)-based single layer, multilayer and sandwich films [1] The sandwich film production is simple with respect to multilayer film, however, it allows to achieve a promising magnetostrictive softness [1,2] In sandwiches, properties such as magnetisation or anisotropy differ from one layer to the next, so the magnetisation reversal occurs at different coercive fields for each layer When the reversal takes place in a given layer but not in the adjacent one, a so-called extended domain wall (EDW) will be formed at the interfaces [3] In this paper, we study the magnetisation process in Fe/Terfecohan/Fe sandwich films The two Fe(tFe)/Terfecohan(tTbFeCo)/Fe(tFe) sandwich films with tTbFeCo ¼ 650 and 570 nm and tFe ¼ 30 and 60 nm (denoted as the samples SW30 and SW60, respectively) were prepared by rf-magnetron sputtering system *Corresponding author Tel.: +84-4-8585281; fax: +84-48584438 E-mail address: duc@netnam.org.vn (N.H Duc) Fig illustrates the magnetic hysteresis loops measured in fields applied parallel and perpendicular to the film plane for the as-deposited SW60 The inplane magnetisation exhibits already a large remanence, but the saturation state requires a magnetic field higher than 0.7 T A similar result is observed for SW30 These features suggest that the magnetisation seems to consist of both perpendicular and parallel magnetic components: the observed remanence is the contribution of the Fe-layers and the large magnetisation curvature reflects the rotation of the Terfecohan magnetisation into the film plane An opposite magnetisation process occurs in the perpendicular magnetic hysteresis loop: the large high-field susceptibility is presently related to the rotation of the Fe magnetic moment out of plane Annealing effect tends to establish the in-plane magnetic anisotropy in the whole sample Finally, one observes a field-induced magnetic transition in samples annealed at TA X450 C (see e.g Fig 2) Such a magnetic behaviour is already reported for sandwich films, in which the individual layer thickness is large enough (tX25 nm) and 3d exchange interactions ensure parallel coupling of the Fe(Co) moments throughout the entire thickness of the sandwich [3,4] In these films, it is 0304-8853/$ - see front matter r 2003 Elsevier B.V All rights reserved doi:10.1016/j.jmmm.2003.12.892 ARTICLE IN PRESS e1598 N.H Duc et al / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1597–e1599 Fig Hysteresis loops of the as-deposited SW60 Fig Magnetic (a) and magnetostrictive (b) hysteresis loops of the 450 C-annealed SW30 reasonable to assume that the magnetisation in the TbFeCo layer is dominated by Tb The zero-field magnetic moment configuration can also be schematised in the insert of Fig 2a (phase II) The magnetisation process is described as follows Starting from the positive high-field state, where the magnetisation is well saturated, all the (Terfecohan and Fe) magnetisation components in the sample are parallel to the applied field direction due to the domination of the Zeeman energy It means that the Fe(Co) moments between adjacent layers are antiparallelly coupled In this case, an EDW is formed at the interfaces, Fig 2a (phase I) As the field decreases and changes its direction, the magnetisation reversal occurs initially in the Fe layers at Àmo Ht1 leading to the parallel state of Fe(Co) moments in the whole sample and to the annihilation of EDWs (phase II) When magnetic field reaches to the value Àmo Ht2 the Terfecohan magnetisation is reversed and the EDW is re-established (phase III) Note that while the mo Ht1 (B10 mT) remains almost constant mo Ht2 is nearly doubled when increasing TA from 450 C to 500 C This enhancement of mo Ht2 may be attributed to the crystallisation of the Terfecohan phase leading to the increasing of its intrinsic coercive field [2] Fig 2b presents the field dependence of the parallel magnetostriction (ljj ) for the 450 C-annealed sample SW30 Clearly, the double coercivity character is evidenced: the Fe-magnetisation reversal causes a magnetostriction drop as large as 60 Â 10À6 at Àmo Ht1 and the Terfecohan magnetisation reversal results in the change of sign of the magnetostrictive susceptibility The (negative) perpendicular magnetostriction follows a similar trend These findings, however, are different from those reported in Refs [3,4] The domain wall formation usually causes the TbFeCo moments (in the domain wall volume) to rotate out of the field direction, leading to a negative contribution to the magnetostriction In the samples under investigation, the domain wall width may be much thinner than the TbFeCo thickness Hence, the magnetostriction of the core of the TbFeCo layer is still dominant In order to verify this argument, we present in Fig the magnetostriction data for a strongly reduced Terfecohan layer thickness sample, e.g the {19 nm Terfecohan/11 nm Fe} multilayer For small fields, the layers are still exchange coupled and thus the ordinary (positive) parallel magnetostriction is observed At mo H > 50 mT, the EDW formation results in a negative contribution to the parallel magnetostriction, which is larger than the positive magnetostriction of the TbFeCo core The perpendicular magnetostriction is almost independent to the EDW formation since the magnetic domains are oriented perpendicular to the measured direction [4] In conclusion, different magnetisation processes were evidenced by the magnetisation and magnetostriction investigations The observation of the EDW contribution to magnetostriction, however, strongly depends on its volume fraction with respect to the TbFeCo one Fig Magnetostriction data of the {19 nm Terfecohan/11 nm Fe} multilayer ARTICLE IN PRESS N.H Duc et al / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1597–e1599 This work is supported by the Vietnam National University, Hanoi—project QG.02.06 and the Vietnam– Italian Cooperation in S&T—project 8S3 References [1] N.H Duc, J Magn Magn Mater 212 (2002) 1411 e1599 [2] N.H Duc, D.T Huong Giang, V.N Thuc, N.T Minh Hong, N Chau, Physica B 327 (2003) 328 [3] D Givord, J Betz, K Mackay, J.C Tousaint, J Voiron, S Wuchner, J Magn Magn Mater 159 (1996) 71 [4] E Quandt, A Ludwig, J Appl Phys 85 (1999) 6232  ... TbFeCo moments (in the domain wall volume) to rotate out of the field direction, leading to a negative contribution to the magnetostriction In the samples under investigation, the domain wall width... is described as follows Starting from the positive high-field state, where the magnetisation is well saturated, all the (Terfecohan and Fe) magnetisation components in the sample are parallel to... decreases and changes its direction, the magnetisation reversal occurs initially in the Fe layers at Àmo Ht1 leading to the parallel state of Fe( Co) moments in the whole sample and to the annihilation