Simultaneous measurement of anisotropic magnetoresistance and observation of magnetic domains by Kerr microscopy Julia Osten, Kilian Lenz, Andreas Henschke, Jürgen Lindner, and Jürgen Fassbender Citation: Review of Scientific Instruments 85, 123701 (2014); doi: 10.1063/1.4902839 View online: http://dx.doi.org/10.1063/1.4902839 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/85/12?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Magnetic domain observation of Nd–Cu-diffused Nd–Fe–B magnets with submicron grains by Kerr effect microscopy J. Appl. Phys. 111, 07A714 (2012); 10.1063/1.3675157 Design of a vector magnet for the measurements of anisotropic magnetoresistance and rotational magneto-optic Kerr effect Rev. Sci. Instrum. 83, 033906 (2012); 10.1063/1.3698297 Simultaneous polarized neutron reflectometry and anisotropic magnetoresistance measurements Rev. Sci. Instrum. 82, 033902 (2011); 10.1063/1.3541839 Resistance of domain walls created by means of a magnetic force microscope in transversally magnetized epitaxial Fe wires Appl. Phys. Lett. 95, 032504 (2009); 10.1063/1.3187219 Transmission electron microscopy specimen holder for simultaneous in situ heating and electrical resistance measurements Rev. Sci. Instrum. 75, 426 (2004); 10.1063/1.1611616
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REVIEW OF SCIENTIFIC INSTRUMENTS 85, 123701 (2014)
Simultaneous measurement of anisotropic magnetoresistance and observation of magnetic domains by Kerr microscopy Julia Osten,1,2 Kilian Lenz,1 Andreas Henschke,1 Jürgen Lindner,1 and Jürgen Fassbender1,2,a) 1 Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Bautzner Landstr. 400, 01328 Dresden, Germany 2 Technische Universität Dresden, 01069 Dresden, Germany
(Received 2 October 2014; accepted 15 November 2014; published online 8 December 2014) We report on a new instrument, which consists of a Kerr microscope combined with resistance measurements. This setup allows for the recording of magnetic domains while measuring the anisotropic magnetoresistance (AMR). For this purpose the development of a special sample holder and the extension of the measurement software was required. The sample holder is equipped with electrical contacts in such a way to apply a current, measure the voltage, and use it in the Kerr microscope. The extension of the measurement software enables the recording of resistance and Kerr images simultaneous. The new setup allows for a better microscopic understanding of the AMR behavior. © 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4902839] I. INTRODUCTION
Precise angle measurements as well as accurate determination of magnetic field strengths are an important issue due to their relevance for many applications.1–4 Two recent examples are the measurement of angles in a smart knee prostheses and the detection of the earth magnetic field as a part of a wireless asynchronous data communication module.5, 6 These sensors are based on the AMR (anisotropic magneto resistance) in ferromagnetic materials, discovered by Thomson in 1857.7 AMR depends on the angle between the applied current, and the direction of the internal magnetization. Since changing the orientation of the magnetization may lead to the occurrence of magnetic domains, the specific domain configuration plays an important role for the AMR behavior. Consequently, a combination of Kerr microscopy with simultaneous measurements of the electrical resistance is of benefit. The AMR has its maximum value if the current flows parallel to the internal magnetization, because this gives rise to the highest probability for s-d scattering of the electrons.8 The minimum value occurs if the current flows perpendicularly to the internal magnetization with ϕ H being the angle between the current and the applied field H. Starting with a saturated sample the magnetization is oriented in the direction of the applied field. Kerr microscopy is based on the magneto-optical Kerr effect, which describes the change in polarization of light after reflection from the magnetic surface in dependence on the magnetization of the sample.9 The knowledge about the domain state of the sample with its local magnetization directions is important for the understanding of the resulting resistance behavior. Kerr microscopy can be used, for example, to measure the magnetization reversal process in perpendicular spring magnets and observe the magnetic domains of the outer layer of a rolled-up magnetic nanomembrane.10, 11 Von Hofe et al. a) Author to whom correspondence should be addressed. Electronic mail:
[email protected] 0034-6748/2014/85(12)/123701/4/$30.00
enhanced their microscope in such a way that it is capable of measuring two components of the magnetization at the same time due to dual wavelength magneto-optical imaging.12 Kerr microscopy investigations and AMR measurements on exchange coupled stripes were performed by Trützschler et al.13 They recorded the AMR during a BH-loop with a four-point probe technique and measured the magnetic domains separately. Their motivation for using the Kerr microscope was that small deviation between the predicted AMR and measured one can only be explained with domain observations. Bolte et al. investigated the magnetoresistance of rectangular Permalloy microstructures by magnetic force microscopy (MFM).14 Nevertheless, they could not measure the AMR and simultaneously observe the domain structure due to the interaction of the magnetic tip of the magnetic force microscope with the sample. MFM in combination with AMR measurements were also used by Hassel et al. and Nam.15, 16 They could not measure magnetic domains either the resistance at one time. In contrast the advantage of the Kerr microscopy compared to MFM is that image acquisition is faster (real time) and domains are observed directly.17 Manago et al. investigated the magnetoresistance of zigzag shaped Permalloy wires under different field angles.18 They performed LandauLifschitz-Gilbert simulations for their AMR measurements, but did not record the domain images during the resistance measurements. Hence the advantage of our experimental approach is that we are able to measure the AMR electrically while imaging the domain structure by Kerr microscopy at the same time. II. EXPERIMENT
A Z EISS polarization microscope equipped with a quadrupole electromagnet from E VICO MAGNETICS was used to observe the magnetic domains and to record the hysteresis of the sample section in the field of view (FOV). To measure the AMR during imaging, the sample holder (see Fig. 1) is equipped with electrical contacts in two-point
85, 123701-1
© 2014 AIP Publishing LLC
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Osten et al.
Si substrate
(b) sample contact pads Plug
I H
ϕH
FIG. 1. (a) Sketch of the stripe samples with stripe width w and the coordinate system. Cr+ -implanted Permalloy stripes are depicted in black. (b) Illustration of the sample holder. For all samples the current is applied perpendicularly to the long edge of the stripes. ϕ H denotes the field direction with respect to the current I direction.
geometry. The electrical contacts to the sample are made by silver conducting paint along two of the four sample edges. As shown in Fig. 2, the resistance was measured by a source meter unit consisting of a K EITHLEY ’ S model 6221 current source and a model 2182A nanovoltmeter. The measurements were performed using a modified version of the Kerrlab software (v653) from E VICO MAGNETICS. With this software it is possible to address the quadrupole electromagnet by controlling the power supplies (K EPCO BOP 100-4M and 72-6M), while measuring the resulting field. The program was modified in a way that allowed recording the resistance of the sample during imaging. That means both values are measured at the same time. Note that due to the sample size of around 1 cm2 the Kerr microscope only images a small sample area of about 0.03 mm2 , while the AMR was measured over the complete sample. The investigated samples are 20 nm thick Permalloy (Ni80 Fe20 ) structured hybrid magnetic films on a Si-Wafer with a Ta buffer layer. The structuring was achieved by implantation of Cr+ ions with a fluence of 1.2 × 1016 Cr+ /cm2 and a kinetic energy of 30 keV into the uncovered Permalloy parts (black stripes) next to masked ones (white stripes)
(Fig. 1). Optical lithography was used to prepare the mask. The cause for the hybrid magnetic film is that the magnetic moment of the Cr implanted stripes is approximately 60% of the non-implanted ones.19 Using this system we studied the correlation between AMR and the domain pattern. Two examples are displayed in Figs. 3 and 4. In both graphs (Figs. 3(a) and 4(a)), the hysteresis is plotted with black circles, and the resistance data are shown by filled red circles. For recording the hysteresis, the intensity of the image is measured during a field sweep and normalized to the saturation magnetization Ms at the end of the measurement. Due to the hysteresis effect the graphs are not symmetric to zero field. For better visibility only the ascending branch is displayed. During the field sweep a current is applied to the sample and the AMR is measured. In the diagram the ratio of resistance compared to the saturation resistance Rs in percent is shown. For selected field values there are small letters inside the plot referring to the corresponding domain images below the graph. In Fig. 3, the stripe width is w = 10 μm and the field is applied perpendicularly to the current (ϕ H = 90◦ ). In saturation the AMR is low, because the magnetization of the sample is perpendicular to the current
w= 10 µm
(a)
90° 0.4
loop AMR
1
c
d
0.3
e
e
0.2
0
d
b
0.1
c
s
Py Py+Cr Py Py+Cr Py Py+Cr
R/R [%]
(a) w
Rev. Sci. Instrum. 85, 123701 (2014)
M/Ms
123701-2
0.0
b
-1
-0.1 -1.2
-0.9
-0.6
-0.3
0.0
0.3
0.6
0.9
1.2
H [mT] AMR Keithley 6221
I
(b)
(c)
y-Coils Kepco BOP 72-6M
AMR Keithley 2182A
I
U
Agilent 34410A
20µm 50µm
y
(d)
(e)
x
I x-Coils Kepco BOP 100-4M
Agilent 34410A
FIG. 2. Sketch of the measurement setup. The sample is electrical contacted and located in the middle of the quadrupole electromagnet. The objective of the microscope is above the sample (not shown).
FIG. 3. (a) Hysteresis (black circles) with corresponding AMR measurements (filled red circles) for w=10 μm and ϕ H = 90◦ . The Field (current) direction is denoted by black (dashed red) arrows. (b)–(e) Corresponding domain images taken at field values marked with letters in panel (a). Black (white) rectangles mark implanted (non-implanted) stripes. Short (long) arrows mark the magnetization direction in implanted (non-implanted) stripes.
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Osten et al.
123701-3
w= 20 µm
(a)
Rev. Sci. Instrum. 85, 123701 (2014)
[compare Figs. 4(c)–4(e)]. Hence in this example the evolution of the multiple domain state is crucial to understand the AMR behavior. This can be revealed by the combined AMRKerr microscopy.
=40°
0.00 0
b
c d
b
-0.05
-1
c -1.2
-0.8
-0.4
s
M/Ms
e d e
R/R [%]
0.05 1
0.0
0.4
loop AMR 0.8
1.2
H [mT] (b)
(c)
20µm (d)
(e)
FIG. 4. (a) Hysteresis (black circles) with corresponding AMR measurements (filled red circles) for w = 20 μm and ϕ H = 40◦ . The Field (current) direction is denoted by black (red dashed) arrows. (b)–(e) Corresponding domain images taken at field values marked with letters in panel (a). Black (white) rectangles mark implanted (non-implanted) stripes.
[see Fig. 3(b)]. The remagnetization process, the AMR shows a broad peak. This is due to the fact that the magnetization of the implanted stripes are rotating and the non-implanted ones have not yet switched [see Figs. 3(c) and 3(d)]. During the switching process the magnetization of the stripes aligns parallel to the current, resulting in a higher AMR. The AMR is decreased again when also the virgin stripes have switched, because then the magnetization is again parallel with the field, and therefore perpendicular to the current [Fig. 3(e)]. Only the knowledge about the separate switching of the two stripe types explains the AMR plateau. The other example shown in Fig. 4 is the w = 20 μm stripe sample. In this case, the field is applied at ϕ H = 40◦ with respect to the current direction. The hysteresis curve (black) exhibits a smooth decrease from Figs. 4(b) and 4(c) and a sharp jump from Figs. 4(c)–4(e). The AMR slightly increases until −0.4 mT then it drops until Fig. 4(c). The decrease of the AMR is accompanied by the occurrence and growth of multiple, diamond shaped domains in the non-implanted stripes marked by the white box as depicted in Figs. 4(b) and 4(c). At the minimum of the AMR, this multiple domain state has its maximum size. The following jump in the AMR curve can be explained by the vanishing of the multiple domain state
III. CONCLUSION
In this work, we realized magnetic domain imaging and magnetoresistance measurements at the same time. A specific sample holder in two-point style was designed and allows for measuring the electrical resistance. The holder fits into the Kerr microscope, which is used to observe magnetic domains. Also the software was modified in a way that the magnetic loop and resistance curves are recorded simultaneously. With this setup the electrical resistance can be recorded with a resolution of R/Rs = 0.006% and a signal-to-noiseratio of around 70. Magnetoresistance like AMR, in plane giant magnetoresistance (GMR) and planar Hall-effect can be measured. We investigated stripe patterned Permalloy samples where the ion implanted stripes have a lower saturation magnetization compared to the other ones. In the first example, an antiparallel orientation of the magnetization of two stripes leads to a broad AMR peak. The second example shows that the change in magnetoresistance is slower in the presence of a multiple domain state as compared to the further magnetization reversal after their disappearance. We believe that Kerr microscopy in combination with resistance measurements is a smart tool to gain knowledge about the dependence of the magnetoresistance on the internal magnetization.
ACKNOWLEDGMENTS
We are grateful to R. Kaltofen and C. Krien from IFW Dresden for the help with thin film deposition, I. Mönch for the lithographic processing, and I. Winkler for the ion implantation. J.O. likes to thank Frederik W. Osten for fruitful discussions. This work has been supported by the Deutsche Forschungsgemeinschaft (Grant No. FA316/3-2). 1 J.
Lenz and A. S. Edelstein, IEEE Sensors J. 6, 631 (2006). Ripka and M. Janošek, IEEE Sensors J. 10, 1108 (2010). 3 Y. Yunchun and J. A. Farell, IEEE Trans. Robotics Automation 19, 269 (2003). 4 C.-J. Zhao, L. Ding, J.-S. HuangFu, J.-Y. Zhang, and G.-H. Yu, Rare Met. 32, 213 (2013). 5 Y. Ege, M. Gökhan Sensoy, O. Kalender, S. Nazlibilek, and H. Citak, Measurement 46, 2672 (2013). 6 A. Arami, A. Vallet, and K. Aminian, IEEE Trans. Biomed. Eng. 60, 2504 (2013). 7 W. Thomson, Proc. Royal Soc. London 8, 546 (1857). 8 S. Andreev and P. Dimitrova, J. Optoelectr. Adv. Mater. 7, 199 (2005). 9 W. Rave, R. Schaefer, and A. Hubert, J. Magn. Magn. Mater. 65, 7 (1987). 10 L. Ma, D. A. Gilbert, V. Neu, R. Schaefer, J. G. Zheng, X. Q. Yan, Z. Shi, K. Liu, and S. M. Zhou, J. Appl. Phys. 116, 033922 (2014). 11 R. Streubel, J. Lee, D. Makarov, M.-Y. Im, D. Karnaushenko, L. Han, R. Schäfer, P. Fischer, S.-K. Kim, and O. G. Schmidt, Adv. Mater. 26, 316 (2014). 12 T. von Hofe, N. O. Urs, B. Mozooni, T. Jansen, C. Kirchhof, D. E. Bürgler, E. Quandt, and J. McCord, Appl. Phys. Lett. 103, 142410 (2013). 13 J. Trützschler, K. Sentosun, M. Langer, I. Mönch, R. Mattheis, J. Fassbender, and J. McCord, J. Appl. Phys. 115, 103901 (2014). 2 P.
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123701-4 14 M.
Osten et al.
Bolte, M. Steiner, C. Pels, M. Barthelmess, J. Kruse, U. Merkt, G. Meier, M. Holz, and D. Pfannkuche, Phys. Rev. B 72, 224436 (2005). 15 C. Hassel, S. Stienen, F. M. Rrömer, R. Meckenstock, G. Dumpich, and J. Lindner, Appl. Phys. Lett. 95, 032504 (2009). 16 C. Nam, J. Korean Phys. Soc. 63, 441 (2013).
Rev. Sci. Instrum. 85, 123701 (2014) 17 A.
Hubert and R. Schäfer, Magnetic Domains – The Analysis of Magnetic Microstructures, (Springer, 2000). 18 T. Manago, K. Kanazawa, and T. Kera, J. Magn. Magn. Mater. 321, 2327 (2009). 19 J. Fassbender, J. von Borany, A. Mücklich, K. Potzger, W. Möller, J. McCord, L. Schultz, and R. Mattheis, Phys. Rev. B 73, 184410 (2006).
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 137.99.31.134 On: Wed, 14 Jan 2015 15:48:05
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 137.99.31.134 On: Wed, 14 Jan 2015 15:48:05
REVIEW OF SCIENTIFIC INSTRUMENTS 85, 123701 (2014)
Simultaneous measurement of anisotropic magnetoresistance and observation of magnetic domains by Kerr microscopy Julia Osten,1,2 Kilian Lenz,1 Andreas Henschke,1 Jürgen Lindner,1 and Jürgen Fassbender1,2,a) 1 Helmholtz-Zentrum Dresden-Rossendorf, Institute of Ion Beam Physics and Materials Research, Bautzner Landstr. 400, 01328 Dresden, Germany 2 Technische Universität Dresden, 01069 Dresden, Germany
(Received 2 October 2014; accepted 15 November 2014; published online 8 December 2014) We report on a new instrument, which consists of a Kerr microscope combined with resistance measurements. This setup allows for the recording of magnetic domains while measuring the anisotropic magnetoresistance (AMR). For this purpose the development of a special sample holder and the extension of the measurement software was required. The sample holder is equipped with electrical contacts in such a way to apply a current, measure the voltage, and use it in the Kerr microscope. The extension of the measurement software enables the recording of resistance and Kerr images simultaneous. The new setup allows for a better microscopic understanding of the AMR behavior. © 2014 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4902839] I. INTRODUCTION
Precise angle measurements as well as accurate determination of magnetic field strengths are an important issue due to their relevance for many applications.1–4 Two recent examples are the measurement of angles in a smart knee prostheses and the detection of the earth magnetic field as a part of a wireless asynchronous data communication module.5, 6 These sensors are based on the AMR (anisotropic magneto resistance) in ferromagnetic materials, discovered by Thomson in 1857.7 AMR depends on the angle between the applied current, and the direction of the internal magnetization. Since changing the orientation of the magnetization may lead to the occurrence of magnetic domains, the specific domain configuration plays an important role for the AMR behavior. Consequently, a combination of Kerr microscopy with simultaneous measurements of the electrical resistance is of benefit. The AMR has its maximum value if the current flows parallel to the internal magnetization, because this gives rise to the highest probability for s-d scattering of the electrons.8 The minimum value occurs if the current flows perpendicularly to the internal magnetization with ϕ H being the angle between the current and the applied field H. Starting with a saturated sample the magnetization is oriented in the direction of the applied field. Kerr microscopy is based on the magneto-optical Kerr effect, which describes the change in polarization of light after reflection from the magnetic surface in dependence on the magnetization of the sample.9 The knowledge about the domain state of the sample with its local magnetization directions is important for the understanding of the resulting resistance behavior. Kerr microscopy can be used, for example, to measure the magnetization reversal process in perpendicular spring magnets and observe the magnetic domains of the outer layer of a rolled-up magnetic nanomembrane.10, 11 Von Hofe et al. a) Author to whom correspondence should be addressed. Electronic mail:
[email protected] 0034-6748/2014/85(12)/123701/4/$30.00
enhanced their microscope in such a way that it is capable of measuring two components of the magnetization at the same time due to dual wavelength magneto-optical imaging.12 Kerr microscopy investigations and AMR measurements on exchange coupled stripes were performed by Trützschler et al.13 They recorded the AMR during a BH-loop with a four-point probe technique and measured the magnetic domains separately. Their motivation for using the Kerr microscope was that small deviation between the predicted AMR and measured one can only be explained with domain observations. Bolte et al. investigated the magnetoresistance of rectangular Permalloy microstructures by magnetic force microscopy (MFM).14 Nevertheless, they could not measure the AMR and simultaneously observe the domain structure due to the interaction of the magnetic tip of the magnetic force microscope with the sample. MFM in combination with AMR measurements were also used by Hassel et al. and Nam.15, 16 They could not measure magnetic domains either the resistance at one time. In contrast the advantage of the Kerr microscopy compared to MFM is that image acquisition is faster (real time) and domains are observed directly.17 Manago et al. investigated the magnetoresistance of zigzag shaped Permalloy wires under different field angles.18 They performed LandauLifschitz-Gilbert simulations for their AMR measurements, but did not record the domain images during the resistance measurements. Hence the advantage of our experimental approach is that we are able to measure the AMR electrically while imaging the domain structure by Kerr microscopy at the same time. II. EXPERIMENT
A Z EISS polarization microscope equipped with a quadrupole electromagnet from E VICO MAGNETICS was used to observe the magnetic domains and to record the hysteresis of the sample section in the field of view (FOV). To measure the AMR during imaging, the sample holder (see Fig. 1) is equipped with electrical contacts in two-point
85, 123701-1
© 2014 AIP Publishing LLC
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 137.99.31.134 On: Wed, 14 Jan 2015 15:48:05
Osten et al.
Si substrate
(b) sample contact pads Plug
I H
ϕH
FIG. 1. (a) Sketch of the stripe samples with stripe width w and the coordinate system. Cr+ -implanted Permalloy stripes are depicted in black. (b) Illustration of the sample holder. For all samples the current is applied perpendicularly to the long edge of the stripes. ϕ H denotes the field direction with respect to the current I direction.
geometry. The electrical contacts to the sample are made by silver conducting paint along two of the four sample edges. As shown in Fig. 2, the resistance was measured by a source meter unit consisting of a K EITHLEY ’ S model 6221 current source and a model 2182A nanovoltmeter. The measurements were performed using a modified version of the Kerrlab software (v653) from E VICO MAGNETICS. With this software it is possible to address the quadrupole electromagnet by controlling the power supplies (K EPCO BOP 100-4M and 72-6M), while measuring the resulting field. The program was modified in a way that allowed recording the resistance of the sample during imaging. That means both values are measured at the same time. Note that due to the sample size of around 1 cm2 the Kerr microscope only images a small sample area of about 0.03 mm2 , while the AMR was measured over the complete sample. The investigated samples are 20 nm thick Permalloy (Ni80 Fe20 ) structured hybrid magnetic films on a Si-Wafer with a Ta buffer layer. The structuring was achieved by implantation of Cr+ ions with a fluence of 1.2 × 1016 Cr+ /cm2 and a kinetic energy of 30 keV into the uncovered Permalloy parts (black stripes) next to masked ones (white stripes)
(Fig. 1). Optical lithography was used to prepare the mask. The cause for the hybrid magnetic film is that the magnetic moment of the Cr implanted stripes is approximately 60% of the non-implanted ones.19 Using this system we studied the correlation between AMR and the domain pattern. Two examples are displayed in Figs. 3 and 4. In both graphs (Figs. 3(a) and 4(a)), the hysteresis is plotted with black circles, and the resistance data are shown by filled red circles. For recording the hysteresis, the intensity of the image is measured during a field sweep and normalized to the saturation magnetization Ms at the end of the measurement. Due to the hysteresis effect the graphs are not symmetric to zero field. For better visibility only the ascending branch is displayed. During the field sweep a current is applied to the sample and the AMR is measured. In the diagram the ratio of resistance compared to the saturation resistance Rs in percent is shown. For selected field values there are small letters inside the plot referring to the corresponding domain images below the graph. In Fig. 3, the stripe width is w = 10 μm and the field is applied perpendicularly to the current (ϕ H = 90◦ ). In saturation the AMR is low, because the magnetization of the sample is perpendicular to the current
w= 10 µm
(a)
90° 0.4
loop AMR
1
c
d
0.3
e
e
0.2
0
d
b
0.1
c
s
Py Py+Cr Py Py+Cr Py Py+Cr
R/R [%]
(a) w
Rev. Sci. Instrum. 85, 123701 (2014)
M/Ms
123701-2
0.0
b
-1
-0.1 -1.2
-0.9
-0.6
-0.3
0.0
0.3
0.6
0.9
1.2
H [mT] AMR Keithley 6221
I
(b)
(c)
y-Coils Kepco BOP 72-6M
AMR Keithley 2182A
I
U
Agilent 34410A
20µm 50µm
y
(d)
(e)
x
I x-Coils Kepco BOP 100-4M
Agilent 34410A
FIG. 2. Sketch of the measurement setup. The sample is electrical contacted and located in the middle of the quadrupole electromagnet. The objective of the microscope is above the sample (not shown).
FIG. 3. (a) Hysteresis (black circles) with corresponding AMR measurements (filled red circles) for w=10 μm and ϕ H = 90◦ . The Field (current) direction is denoted by black (dashed red) arrows. (b)–(e) Corresponding domain images taken at field values marked with letters in panel (a). Black (white) rectangles mark implanted (non-implanted) stripes. Short (long) arrows mark the magnetization direction in implanted (non-implanted) stripes.
This article is copyrighted as indicated in the article. Reuse of AIP content is subject to the terms at: http://scitationnew.aip.org/termsconditions. Downloaded to IP: 137.99.31.134 On: Wed, 14 Jan 2015 15:48:05
Osten et al.
123701-3
w= 20 µm
(a)
Rev. Sci. Instrum. 85, 123701 (2014)
[compare Figs. 4(c)–4(e)]. Hence in this example the evolution of the multiple domain state is crucial to understand the AMR behavior. This can be revealed by the combined AMRKerr microscopy.
=40°
0.00 0
b
c d
b
-0.05
-1
c -1.2
-0.8
-0.4
s
M/Ms
e d e
R/R [%]
0.05 1
0.0
0.4
loop AMR 0.8
1.2
H [mT] (b)
(c)
20µm (d)
(e)
FIG. 4. (a) Hysteresis (black circles) with corresponding AMR measurements (filled red circles) for w = 20 μm and ϕ H = 40◦ . The Field (current) direction is denoted by black (red dashed) arrows. (b)–(e) Corresponding domain images taken at field values marked with letters in panel (a). Black (white) rectangles mark implanted (non-implanted) stripes.
[see Fig. 3(b)]. The remagnetization process, the AMR shows a broad peak. This is due to the fact that the magnetization of the implanted stripes are rotating and the non-implanted ones have not yet switched [see Figs. 3(c) and 3(d)]. During the switching process the magnetization of the stripes aligns parallel to the current, resulting in a higher AMR. The AMR is decreased again when also the virgin stripes have switched, because then the magnetization is again parallel with the field, and therefore perpendicular to the current [Fig. 3(e)]. Only the knowledge about the separate switching of the two stripe types explains the AMR plateau. The other example shown in Fig. 4 is the w = 20 μm stripe sample. In this case, the field is applied at ϕ H = 40◦ with respect to the current direction. The hysteresis curve (black) exhibits a smooth decrease from Figs. 4(b) and 4(c) and a sharp jump from Figs. 4(c)–4(e). The AMR slightly increases until −0.4 mT then it drops until Fig. 4(c). The decrease of the AMR is accompanied by the occurrence and growth of multiple, diamond shaped domains in the non-implanted stripes marked by the white box as depicted in Figs. 4(b) and 4(c). At the minimum of the AMR, this multiple domain state has its maximum size. The following jump in the AMR curve can be explained by the vanishing of the multiple domain state
III. CONCLUSION
In this work, we realized magnetic domain imaging and magnetoresistance measurements at the same time. A specific sample holder in two-point style was designed and allows for measuring the electrical resistance. The holder fits into the Kerr microscope, which is used to observe magnetic domains. Also the software was modified in a way that the magnetic loop and resistance curves are recorded simultaneously. With this setup the electrical resistance can be recorded with a resolution of R/Rs = 0.006% and a signal-to-noiseratio of around 70. Magnetoresistance like AMR, in plane giant magnetoresistance (GMR) and planar Hall-effect can be measured. We investigated stripe patterned Permalloy samples where the ion implanted stripes have a lower saturation magnetization compared to the other ones. In the first example, an antiparallel orientation of the magnetization of two stripes leads to a broad AMR peak. The second example shows that the change in magnetoresistance is slower in the presence of a multiple domain state as compared to the further magnetization reversal after their disappearance. We believe that Kerr microscopy in combination with resistance measurements is a smart tool to gain knowledge about the dependence of the magnetoresistance on the internal magnetization.
ACKNOWLEDGMENTS
We are grateful to R. Kaltofen and C. Krien from IFW Dresden for the help with thin film deposition, I. Mönch for the lithographic processing, and I. Winkler for the ion implantation. J.O. likes to thank Frederik W. Osten for fruitful discussions. This work has been supported by the Deutsche Forschungsgemeinschaft (Grant No. FA316/3-2). 1 J.
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