Journal of Magnetism and Magnetic Materials 272–276 2004 e1597–e1599Magnetisation and magnetostriction in Fe/Terfecohan/Fe sandwichfilms withan extended domain wall formation N.H.. Richom
Trang 1Journal of Magnetism and Magnetic Materials 272–276 (2004) e1597–e1599
Magnetisation and magnetostriction in Fe/Terfecohan/Fe sandwichfilms withan 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, Universit "a di Roma ‘‘Tor Vergata’’, via della Ricerca Scientifica 1, Roma 00133, Italy
c
GPM-UMR 6634, Universit !e 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 sandwichfilms with
an individual TbFeCo-layer thickness of about 600 nm and Fe-layer thickness tFe¼ 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
r2003 Elsevier B.V All rights reserved
PACS: 75.60.Jk; 75.70.Ak; 75.80.+q
Keywords: Magnetization process; Magnetostriction; Domain wall; Sandwichfilms
Giant low-field magnetostriction has been extensively
studied in amorphous Tb(Fe0.55Co0.45)1.5(denoted as
a-Terfecohan)-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 suchas magnetisation or anisotropy differ
from one layer to the next, so the magnetisation reversal
occurs at different coercive fields for eachlayer 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
sandwichfilms
The two Fe(tFe)/Terfecohan(tTbFeCo)/Fe(tFe)
sand-wichfilms withtTbFeCo¼ 650 and 570 nm and tFe¼ 30
and 60 nm (denoted as the samples SW30 and SW60,
respectively) were prepared by rf-magnetron sputtering
system
Fig 1 illustrates the magnetic hysteresis loops measured in fields applied parallel and perpendicular
to the film plane for the as-deposited SW60 The in-plane 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 bothperpendicular and parallel magnetic compo-nents: 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 establishthe in-plane magnetic anisotropy in the whole sample Finally, one observes a field-induced magnetic transition in samples annealed at TAX450C (see e.g Fig 2) Sucha 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
*Corresponding author Tel.: 8585281; fax:
+84-4-8584438.
E-mail address: duc@netnam.org.vn (N.H Duc).
0304-8853/$ - see front matter r 2003 Elsevier B.V All rights reserved.
doi:10.1016/j.jmmm.2003.12.892
Trang 2reasonable 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 moHt1 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 moHt2the Terfecohan magnetisation is reversed and the EDW is re-established (phase III) Note that while the moHt1 (B10 mT) remains almost constant
moHt2is nearly doubled when increasing TAfrom 450C
to 500C This enhancement of moHt2may 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 450C-annealed sample SW30 Clearly, the double coercivity character is evidenced: the Fe-magnetisation reversal causes a magnetostriction drop as large as 60 106at moHt1 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 magnetostric-tion 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 moH > 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 contribu-tion to magnetostriccontribu-tion, however, strongly depends on its volume fraction withrespect to the TbFeCo one
Fig 1 Hysteresis loops of the as-deposited SW60.
Fig 2 Magnetic (a) and magnetostrictive (b) hysteresis loops
of the 450 C-annealed SW30.
Fig 3 Magnetostriction data of the {19 nm Terfecohan/11 nm Fe} multilayer.
Trang 3This 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.
[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 W uchner, J Magn Magn Mater 159 (1996) 71 [4] E Quandt, A Ludwig, J Appl Phys 85 (1999) 6232.