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YFe2 multilayer film
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 272–276 (2004) 1943–1944
Giant magneto and anisotropic resistance in an epitaxial (1 1 0) DyFe2/YFe2 multilayer film J-M.L. Beaujoura, G.J. Bowdena, A.A. Zhukova, J.D. O’Neill, B.D. Rainforda, P.A.J. de Groota,*, R.C.C. Wardb, M.R. Wellsb, A.G.M. Jansenc a
Department of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK b Clarendon Laboratory, Oxford University, Oxford OX1 3PU, UK c Grenoble High Magnetic Field Laboratory, MPIF and CNRS, Grenoble Cedex 9 F-38042, France
Abstract Anisotropic and giant magneto-resistance (AMR and GMR) measurements for a molecular beam epitaxy grown ( ( (1 1 0) multilayer film [50 A-DyFe 2/50 A-YFe2] 40 at 100 K are reported. The film possesses a bending field BBB5 T and an irreversible switching field BISB5 T. These features allow the study of both AMR, and GMR caused by the creation not only of longitudinal but also transverse magnetic exchange springs, in the magnetically soft YFe2 layers. Finally, rotation experiments in applied fields show that like DyFe2 films, there is a metastable state aligned along a ½1% 1 0 axis at 100 K. r 2004 Elsevier B.V. All rights reserved. PACS: 75.30.Gw; 75.47.De; 75.50.Gg; 75.70.Cn Keywords: Epitaxy; Rare-earth transition metals; Anisotropic magnetoresistance; Giant magnetoresistance; Thin magnetic films; Magnetic exchange springs
Giant magnetoresistance (GMR) in epitaxial (1 1 0) DyFe2/YFe2 multilayers, was first reported in Ref. [1]. More recently, rotation experiments performed on (1 1 0) DyFe2 films show the presence of a metastable state in DyFe2 at 100 K. This feature allows a precise determination to be made of the anisotropic magnetoresistance (AMR) for magnetisations directed along the in-plane [0 0 1] and ½1% 1 0 axes. In this paper, it is shown that similar results can be obtained for a ( ( multilayer [50 A-DyFe 2/50 A-YFe2] 18 film. But in addition, GMR occurs in both longitudinal and transverse magnetic exchange springs. ( films were grown by molecular beam The 4000 A epitaxy (MBE), using a Balzers UMS 630 UHV facility [3,4]. The sample was prepared for transport measurements as described in Ref. [2]. The rig allowed the *Corresponding author. Tel.: +44-23-80592110; fax: +4423-80593910. E-mail address: [email protected] (P.A.J. de Groot).
sample to be rotated through 90 , with the magnetic field in the plane of the film. Transport measurements were performed in fields of up to 20 T, at 100 K. To avoid problems associated with sample geometry (B4 0.5 mm2), the results presented below are in terms of the dimensionless quantity Dr=r ¼ ½rðBapp Þ rðBapp ¼ 0Þ=rðBapp ¼ 0Þ:
ð1Þ
In all cases, the sample was polarised in a negative field of 20 T, applied along the [0 0 1] axis, prior to sweeping from 0-20-0 T. The magnetoresistance curves for a field applied along the [0 0 1] axis can be seen in Fig. 1. There is a small positive AMR excursion of some 0.7% in Dr> /r> at about 5 T. This is associated with the irreversible switching of the multilayer film at BISB5 T. Thereafter, the resistivity steadily increases reaching a maximum of 3.95% at 20 T. This monotonic increase is due to GMR caused by the creation of magnetic exchange springs in the soft YFe2 layers [1]. When the magnetic field is swept back down to zero (lower curve), the change in
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.1193
ARTICLE IN PRESS 1944
J.-M.L. Beaujour et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 1943–1944
Fig. 1. Dr=r v: Bapp, for Bapp || [0 0 1]. Fig. 2. Dr=r v: Bapp, after rotation (see text).
resistivity is reversible: a classic signature of a magnetic exchange spring. Similar effects can be seen in Fig. 1(b), but the expected AMR downturn in Drjj /rjj is masked by the upturn in GMR. Finally, we note that there is a small but noticeable anisotropy in the two GMR maxima of Dr> /r> (3.95%) and Drjj /rjj (3.45%). Transport measurements with the field applied along a ½1% 1 0 axis closely mirror those of Fig. 1. At first sight this is surprising, since this implies that the [0 0 1] and ½1% 1 0 are both magnetic easy axes. Like DyFe2 therefore, there is a metastable magnetic state along the ½1% 1 0 axis, but this time in a DyFe2/YFe2 multilayer film. The GMR caused by the magnetic exchange springs in both cases are almost identical. To probe this point still further, rotational experiments were performed. Initially, the sample was magnetically saturated, with field applied along a [0 0 1] axis. Subsequently, the field was reduced to zero and the sample rotated through 90 , so that the direction of the applied field is along the ½1% 1 0 axis. In this rotated configuration the field was swept from 0-20-0 T. The results are shown in Fig. 2. Note that there is an initial rise in resistivity below 5 T, in both rjj and r> : We attribute this to GMR arising from transverse exchange springs, for which the bending field BB=0. Partial loops for field excursions up to 3.5 T were found to be reversible. But for fields above 5 T, the
magnetisation rotates through 90 , giving rise to AMR, and then to GMR following the creation of longitudinal exchange springs, reaching some 3.52% at 20 T. However, on reducing the magnetic field back down to 0 T, the transport measurements exhibit reversible magnetic spring behaviour until B5 T, where the two resistivity curves depart. We find that the final resistivity is some 0.5% higher than its initial value. As for the DyFe2 film [2], we attribute this difference to the AMR appropriate for the [0 0 1] and ½1% 1 0 directions of magnetisation, respectively. In the absence of domains, this allows a precise determination to be made of the AMR. We find that the AMR step at Bapp=0 is B0.5%, smaller than that in DyFe2 (B2%) [2]. This suggests that any AMR present in the DyFe2/YFe2 multilayer is due to the DyFe2 layers. Resistivity measurements on pure YFe2 films confirm this.
References [1] S.N. Gordeev, et al., Phys. Rev. Lett. 87 (2001) 186808. [2] J-M.L. Beaujour, et al., J. Magn. Magn. Mater. 257 (2003) 270. [3] V. Oderno, et al., Phys. Rev. B 54 (1996) R17375-8. [4] M. Sawicki, et al., J. Appl. Phys. 87 (2000) 6839.
Journal of Magnetism and Magnetic Materials 272–276 (2004) 1943–1944
Giant magneto and anisotropic resistance in an epitaxial (1 1 0) DyFe2/YFe2 multilayer film J-M.L. Beaujoura, G.J. Bowdena, A.A. Zhukova, J.D. O’Neill, B.D. Rainforda, P.A.J. de Groota,*, R.C.C. Wardb, M.R. Wellsb, A.G.M. Jansenc a
Department of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK b Clarendon Laboratory, Oxford University, Oxford OX1 3PU, UK c Grenoble High Magnetic Field Laboratory, MPIF and CNRS, Grenoble Cedex 9 F-38042, France
Abstract Anisotropic and giant magneto-resistance (AMR and GMR) measurements for a molecular beam epitaxy grown ( ( (1 1 0) multilayer film [50 A-DyFe 2/50 A-YFe2] 40 at 100 K are reported. The film possesses a bending field BBB5 T and an irreversible switching field BISB5 T. These features allow the study of both AMR, and GMR caused by the creation not only of longitudinal but also transverse magnetic exchange springs, in the magnetically soft YFe2 layers. Finally, rotation experiments in applied fields show that like DyFe2 films, there is a metastable state aligned along a ½1% 1 0 axis at 100 K. r 2004 Elsevier B.V. All rights reserved. PACS: 75.30.Gw; 75.47.De; 75.50.Gg; 75.70.Cn Keywords: Epitaxy; Rare-earth transition metals; Anisotropic magnetoresistance; Giant magnetoresistance; Thin magnetic films; Magnetic exchange springs
Giant magnetoresistance (GMR) in epitaxial (1 1 0) DyFe2/YFe2 multilayers, was first reported in Ref. [1]. More recently, rotation experiments performed on (1 1 0) DyFe2 films show the presence of a metastable state in DyFe2 at 100 K. This feature allows a precise determination to be made of the anisotropic magnetoresistance (AMR) for magnetisations directed along the in-plane [0 0 1] and ½1% 1 0 axes. In this paper, it is shown that similar results can be obtained for a ( ( multilayer [50 A-DyFe 2/50 A-YFe2] 18 film. But in addition, GMR occurs in both longitudinal and transverse magnetic exchange springs. ( films were grown by molecular beam The 4000 A epitaxy (MBE), using a Balzers UMS 630 UHV facility [3,4]. The sample was prepared for transport measurements as described in Ref. [2]. The rig allowed the *Corresponding author. Tel.: +44-23-80592110; fax: +4423-80593910. E-mail address: [email protected] (P.A.J. de Groot).
sample to be rotated through 90 , with the magnetic field in the plane of the film. Transport measurements were performed in fields of up to 20 T, at 100 K. To avoid problems associated with sample geometry (B4 0.5 mm2), the results presented below are in terms of the dimensionless quantity Dr=r ¼ ½rðBapp Þ rðBapp ¼ 0Þ=rðBapp ¼ 0Þ:
ð1Þ
In all cases, the sample was polarised in a negative field of 20 T, applied along the [0 0 1] axis, prior to sweeping from 0-20-0 T. The magnetoresistance curves for a field applied along the [0 0 1] axis can be seen in Fig. 1. There is a small positive AMR excursion of some 0.7% in Dr> /r> at about 5 T. This is associated with the irreversible switching of the multilayer film at BISB5 T. Thereafter, the resistivity steadily increases reaching a maximum of 3.95% at 20 T. This monotonic increase is due to GMR caused by the creation of magnetic exchange springs in the soft YFe2 layers [1]. When the magnetic field is swept back down to zero (lower curve), the change in
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2003.12.1193
ARTICLE IN PRESS 1944
J.-M.L. Beaujour et al. / Journal of Magnetism and Magnetic Materials 272–276 (2004) 1943–1944
Fig. 1. Dr=r v: Bapp, for Bapp || [0 0 1]. Fig. 2. Dr=r v: Bapp, after rotation (see text).
resistivity is reversible: a classic signature of a magnetic exchange spring. Similar effects can be seen in Fig. 1(b), but the expected AMR downturn in Drjj /rjj is masked by the upturn in GMR. Finally, we note that there is a small but noticeable anisotropy in the two GMR maxima of Dr> /r> (3.95%) and Drjj /rjj (3.45%). Transport measurements with the field applied along a ½1% 1 0 axis closely mirror those of Fig. 1. At first sight this is surprising, since this implies that the [0 0 1] and ½1% 1 0 are both magnetic easy axes. Like DyFe2 therefore, there is a metastable magnetic state along the ½1% 1 0 axis, but this time in a DyFe2/YFe2 multilayer film. The GMR caused by the magnetic exchange springs in both cases are almost identical. To probe this point still further, rotational experiments were performed. Initially, the sample was magnetically saturated, with field applied along a [0 0 1] axis. Subsequently, the field was reduced to zero and the sample rotated through 90 , so that the direction of the applied field is along the ½1% 1 0 axis. In this rotated configuration the field was swept from 0-20-0 T. The results are shown in Fig. 2. Note that there is an initial rise in resistivity below 5 T, in both rjj and r> : We attribute this to GMR arising from transverse exchange springs, for which the bending field BB=0. Partial loops for field excursions up to 3.5 T were found to be reversible. But for fields above 5 T, the
magnetisation rotates through 90 , giving rise to AMR, and then to GMR following the creation of longitudinal exchange springs, reaching some 3.52% at 20 T. However, on reducing the magnetic field back down to 0 T, the transport measurements exhibit reversible magnetic spring behaviour until B5 T, where the two resistivity curves depart. We find that the final resistivity is some 0.5% higher than its initial value. As for the DyFe2 film [2], we attribute this difference to the AMR appropriate for the [0 0 1] and ½1% 1 0 directions of magnetisation, respectively. In the absence of domains, this allows a precise determination to be made of the AMR. We find that the AMR step at Bapp=0 is B0.5%, smaller than that in DyFe2 (B2%) [2]. This suggests that any AMR present in the DyFe2/YFe2 multilayer is due to the DyFe2 layers. Resistivity measurements on pure YFe2 films confirm this.
References [1] S.N. Gordeev, et al., Phys. Rev. Lett. 87 (2001) 186808. [2] J-M.L. Beaujour, et al., J. Magn. Magn. Mater. 257 (2003) 270. [3] V. Oderno, et al., Phys. Rev. B 54 (1996) R17375-8. [4] M. Sawicki, et al., J. Appl. Phys. 87 (2000) 6839.