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

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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: (N.H. Duc).

Fig. 1 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


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N.H. Duc et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) e1597–e1599

Fig. 1. Hysteresis loops of the as-deposited SW60.

Fig. 2. 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. 3 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. 3. Magnetostriction data of the {19 nm Terfecohan/11 nm
Fe} multilayer.


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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.

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[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,
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J. Magn. Magn. Mater. 159 (1996) 71.
[4] E. Quandt, A. Ludwig, J. Appl. Phys. 85 (1999) 6232.