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Scanning Hall probe microscopy with high resolution of magnetic field image
ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 282 (2004) 369–372
Scanning Hall probe microscopy with high resolution of magnetic field image M. Shimizua,*, E. Saitoha, H. Miyajimaa, H. Masudab a
Department of Physics, Faculty of Science and Technology, Keio University, Hiyoshi 3-14-1, Kohoku-Ku, Yokohama, Kanagawa 223-8522, Japan b Toei Industry Co., Ltd., 1-8-13, Tadao, Machida 194-0035, Japan Available online 3 May 2004
Abstract The scanning Hall probe microscope (SHPM) which can be used in magnetic fields up to 15 kOe has been developed. A surface magnetic image in the ferromagnetic SmCo5 film was measured under magnetic fields perpendicular to the sample with the SHPM. The observed images describe domain transitions consistent with the magnetization curve. r 2004 Elsevier B.V. All rights reserved. PACS: 07.79. V; 68.37. d Keywords: Scanning probe microscopy; Magnetic imaging; Hall effect
1. Introduction The invention and development of scanning probe microscopy such as scanning tunneling microscopy (STM) [1] and atomic force microscopy [2] have provided powerful yet inexpensive tools for looking at atomic-scale surface structure of a wide variety of materials. Especially for magnetic materials, magnetic force microscopy [3], scanning superconducting-quantum-interface-device microscopy [4] and spin-polarization-tunneling microscopy [5,6] have been applied to obtain surface magnetic images in remanent magnetization state. Recently, scanning Hall probe microscopy (SHPM) [7] has been developed to combine the advantages of these scanning probe micro*Corresponding author. Tel./fax: +81-45-566-1677. E-mail address: [email protected] (M. Shimizu).
scopes with magnetic Hall sensor techniques. Hall sensors with excellent sensitivity and high linearity over a large magnetic-field range allow us to measure the surface stray magnetic field even under the application of a magnetic field. Due to these advantages, SHPM can be used to study field-dependent magnetic domain structures in ferromagnets. In this study, a SHPM system has been developed and the magnetic-field dependence of the surface magnetic structure of a ferromagnetic SmCo5 film have been investigated using the SHPM system.
2. Experiment Fig. 1 is the schematic diagram for a SHPM system developed in the present study. A scanning
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.04.086
ARTICLE IN PRESS M. Shimizu et al. / Journal of Magnetism and Magnetic Materials 282 (2004) 369–372
370
Cryostat Lead-in rail
Stage control amplifer Gause meter SHPM drive unit Display Printer
Electromagnet Vibration reducer
PC based controller
(a) Liq He
Gas He
Cryostat Fig. 2. A STM image of a diffraction grating. The interval of the slit is 1 mm:
x-axis piezo sample stage Hall probe
y
x-axis stepping motor z
(b)
Drive shaft z-axis piezo
z-axis x stepping y-axis piezo motor
Bellows y-axis stepping motor
Fig. 1. The schematic diagram for (a) the SHPM system and (b) the scanning stage.
probe and a scanning stage are enclosed in a cryostat. The cryostat is installed in the gap of the electromagnet which generates the magnetic field upto 15 kOe perpendicular to the sample surface. The scanning stage is made of non-magnetic stainless and sapphire balls to avoid magnetization and magnetostriction of the scanning devices. As shown in Fig. 1(b), the stage is driven by stepping motors and piezo actuators which are installed outside the cryostat and free from the magnetic field. The Hall probe used in this study was fabricated on the edge of the GaAs/AlGaAs heterostructure. The size of active area of the Hall probe is about 10 mm 10 mm: The Hall probe is at the end of the shaft installed on the z-direction actuator. The measuring procedure is as follows: First, the sample mounted on the x–y scanning stage is set below the probe by using the stepping motor.
Next, the probe is approached near the sample surface by monitoring the tunnel current by controlling the z-axis actuator. At last, a STM image (surface topograph) or a SHPM image is measured by using the x- and y-axis piezo actuators. For a resolution test of the scanning system, the gold-coated cross-diffraction grating (1000 lines/ mm) was measured in the STM mode. Fig. 2 shows the obtained topological image. Here, the size of image is 10 mm 10 mm and the total number of pixels is 100 100: The STM image has clear grid patterns, which demonstrates that the scanning stage of the present SHPM system has the position resolution of finer than 1 mm: To demonstrate the performance of the SHPM system, stray field images at the surface of a ferromagnetic SmCo5 film (width: 2:5 length: 3:5 thickness: 0:1 mm) was observed using the system.
3. Results and discussion Fig. 3 shows the magnetization curve for the SmCo5 film used in the present study measured with a vibrating sample magnetometer. The magnetic field was applied perpendicular to the plane of the film. The observed hysteresis loop (miner loop) shows that the sample is not saturated even at 15 kOe:
ARTICLE IN PRESS M. Shimizu et al. / Journal of Magnetism and Magnetic Materials 282 (2004) 369–372
Magnetization M (emu)
1.0 0.5 0.0 -0.5 -1.0 -20 -15 -10 -5 0 5 10 15 20 External Magnetic field Hext (kOe)
Fig. 3. The magnetization curve of a SmCo5 film observed with an application of magnetic field perpendicular to the plane.
371
the increasing magnetic field perpendicular to the film. The results are consistent with the hysteresis curve. A previous literature [6] reported few mm-sized domains in a SmCo5 film, which were not detected in this study. This is mainly because, the active area of the Hall probe used in this study is larger than the domain size, which results in causegraining. Another possibility may be that the Hall probe was poorly approached by the sample surface. The images in the high magnetic field appear to distract along the x direction, which may be the creep of the z actuator, though none of the images mismatch. All the results presented above demonstrate that the SHPM system developed in this study can be used for observing remanent states as well as measurements in the applied magnetic field. Smaller Hall probes are required for the higher resolution of the images.
4. Conclusions
Fig. 4. The external magnetic field dependence of SHPM images for a SmCo5 film. The magnetic field is applied perpendicular to the film plane.
The surface images for the SmCo5 film observed by varying the applied fields between 0 and 15 kOe are shown in Fig. 4. The magnetic field is perpendicular to the film. Before the measurement, the magnetic field of 15 kOe was applied to the sample. The stray field images in the external magnetic field were obtained by subtracting the external magnetic field contribution. The size of the images is 50 mm 50 mm and the number of pixels is 100 100: The black and white regions in Fig. 4 are domains with positive and negative zcomponent of the magnetization. The white region grows with increasing magnetic field, which corresponds to the magnetization process with
The scanning Hall probe microscopes (SHPM) which can be used even in magnetic fields, have been developed. The field dependence of the surface magnetic image for a ferromagnetic SmCo5 film was observed under the magnetic field up to 15 kOe using the SHPM system.
Acknowledgements A part of this work was supported by a Grantin-Aid from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
References [1] G. Binning, H. Rohrer, Sci. Am. 253 (1985) 50. [2] G. Binning, C.F. Quate, Ch. Gerber, Phys. Rev. Lett. 56 (1986) 930. [3] Y. Martin, D. Rugar, H.K. Wickramasinghe, Appl. Phys. Lett. 52 (1988) 244.
ARTICLE IN PRESS 372
M. Shimizu et al. / Journal of Magnetism and Magnetic Materials 282 (2004) 369–372
[4] C.C. Tsuei, J.R. Kirtly, C.C. Chi, L.S. Yu-Jahnes, A. Gupta, T. Shaw, J.Z. Sun, M.B. Ketchen, Phys. Rev. Lett. 73 (1994) 593. [5] M. Johnson, J. Clarke, J. Appl. Phys. 67 (1990) 6141.
[6] T. Kohashi, K. Koike, Jpn. J. Appl. Phys. 40 (2001) 1264. [7] A.M. Chang, H.D. Hallen, L. Harriot, H.F. Hess, H.L. Kao, J. Kwo, R.E. Miller, R. Wolte, J. van der Ziel, T.Y. Chang, Appl. Phys. Lett. 61 (1992) 1974.
Journal of Magnetism and Magnetic Materials 282 (2004) 369–372
Scanning Hall probe microscopy with high resolution of magnetic field image M. Shimizua,*, E. Saitoha, H. Miyajimaa, H. Masudab a
Department of Physics, Faculty of Science and Technology, Keio University, Hiyoshi 3-14-1, Kohoku-Ku, Yokohama, Kanagawa 223-8522, Japan b Toei Industry Co., Ltd., 1-8-13, Tadao, Machida 194-0035, Japan Available online 3 May 2004
Abstract The scanning Hall probe microscope (SHPM) which can be used in magnetic fields up to 15 kOe has been developed. A surface magnetic image in the ferromagnetic SmCo5 film was measured under magnetic fields perpendicular to the sample with the SHPM. The observed images describe domain transitions consistent with the magnetization curve. r 2004 Elsevier B.V. All rights reserved. PACS: 07.79. V; 68.37. d Keywords: Scanning probe microscopy; Magnetic imaging; Hall effect
1. Introduction The invention and development of scanning probe microscopy such as scanning tunneling microscopy (STM) [1] and atomic force microscopy [2] have provided powerful yet inexpensive tools for looking at atomic-scale surface structure of a wide variety of materials. Especially for magnetic materials, magnetic force microscopy [3], scanning superconducting-quantum-interface-device microscopy [4] and spin-polarization-tunneling microscopy [5,6] have been applied to obtain surface magnetic images in remanent magnetization state. Recently, scanning Hall probe microscopy (SHPM) [7] has been developed to combine the advantages of these scanning probe micro*Corresponding author. Tel./fax: +81-45-566-1677. E-mail address: [email protected] (M. Shimizu).
scopes with magnetic Hall sensor techniques. Hall sensors with excellent sensitivity and high linearity over a large magnetic-field range allow us to measure the surface stray magnetic field even under the application of a magnetic field. Due to these advantages, SHPM can be used to study field-dependent magnetic domain structures in ferromagnets. In this study, a SHPM system has been developed and the magnetic-field dependence of the surface magnetic structure of a ferromagnetic SmCo5 film have been investigated using the SHPM system.
2. Experiment Fig. 1 is the schematic diagram for a SHPM system developed in the present study. A scanning
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.jmmm.2004.04.086
ARTICLE IN PRESS M. Shimizu et al. / Journal of Magnetism and Magnetic Materials 282 (2004) 369–372
370
Cryostat Lead-in rail
Stage control amplifer Gause meter SHPM drive unit Display Printer
Electromagnet Vibration reducer
PC based controller
(a) Liq He
Gas He
Cryostat Fig. 2. A STM image of a diffraction grating. The interval of the slit is 1 mm:
x-axis piezo sample stage Hall probe
y
x-axis stepping motor z
(b)
Drive shaft z-axis piezo
z-axis x stepping y-axis piezo motor
Bellows y-axis stepping motor
Fig. 1. The schematic diagram for (a) the SHPM system and (b) the scanning stage.
probe and a scanning stage are enclosed in a cryostat. The cryostat is installed in the gap of the electromagnet which generates the magnetic field upto 15 kOe perpendicular to the sample surface. The scanning stage is made of non-magnetic stainless and sapphire balls to avoid magnetization and magnetostriction of the scanning devices. As shown in Fig. 1(b), the stage is driven by stepping motors and piezo actuators which are installed outside the cryostat and free from the magnetic field. The Hall probe used in this study was fabricated on the edge of the GaAs/AlGaAs heterostructure. The size of active area of the Hall probe is about 10 mm 10 mm: The Hall probe is at the end of the shaft installed on the z-direction actuator. The measuring procedure is as follows: First, the sample mounted on the x–y scanning stage is set below the probe by using the stepping motor.
Next, the probe is approached near the sample surface by monitoring the tunnel current by controlling the z-axis actuator. At last, a STM image (surface topograph) or a SHPM image is measured by using the x- and y-axis piezo actuators. For a resolution test of the scanning system, the gold-coated cross-diffraction grating (1000 lines/ mm) was measured in the STM mode. Fig. 2 shows the obtained topological image. Here, the size of image is 10 mm 10 mm and the total number of pixels is 100 100: The STM image has clear grid patterns, which demonstrates that the scanning stage of the present SHPM system has the position resolution of finer than 1 mm: To demonstrate the performance of the SHPM system, stray field images at the surface of a ferromagnetic SmCo5 film (width: 2:5 length: 3:5 thickness: 0:1 mm) was observed using the system.
3. Results and discussion Fig. 3 shows the magnetization curve for the SmCo5 film used in the present study measured with a vibrating sample magnetometer. The magnetic field was applied perpendicular to the plane of the film. The observed hysteresis loop (miner loop) shows that the sample is not saturated even at 15 kOe:
ARTICLE IN PRESS M. Shimizu et al. / Journal of Magnetism and Magnetic Materials 282 (2004) 369–372
Magnetization M (emu)
1.0 0.5 0.0 -0.5 -1.0 -20 -15 -10 -5 0 5 10 15 20 External Magnetic field Hext (kOe)
Fig. 3. The magnetization curve of a SmCo5 film observed with an application of magnetic field perpendicular to the plane.
371
the increasing magnetic field perpendicular to the film. The results are consistent with the hysteresis curve. A previous literature [6] reported few mm-sized domains in a SmCo5 film, which were not detected in this study. This is mainly because, the active area of the Hall probe used in this study is larger than the domain size, which results in causegraining. Another possibility may be that the Hall probe was poorly approached by the sample surface. The images in the high magnetic field appear to distract along the x direction, which may be the creep of the z actuator, though none of the images mismatch. All the results presented above demonstrate that the SHPM system developed in this study can be used for observing remanent states as well as measurements in the applied magnetic field. Smaller Hall probes are required for the higher resolution of the images.
4. Conclusions
Fig. 4. The external magnetic field dependence of SHPM images for a SmCo5 film. The magnetic field is applied perpendicular to the film plane.
The surface images for the SmCo5 film observed by varying the applied fields between 0 and 15 kOe are shown in Fig. 4. The magnetic field is perpendicular to the film. Before the measurement, the magnetic field of 15 kOe was applied to the sample. The stray field images in the external magnetic field were obtained by subtracting the external magnetic field contribution. The size of the images is 50 mm 50 mm and the number of pixels is 100 100: The black and white regions in Fig. 4 are domains with positive and negative zcomponent of the magnetization. The white region grows with increasing magnetic field, which corresponds to the magnetization process with
The scanning Hall probe microscopes (SHPM) which can be used even in magnetic fields, have been developed. The field dependence of the surface magnetic image for a ferromagnetic SmCo5 film was observed under the magnetic field up to 15 kOe using the SHPM system.
Acknowledgements A part of this work was supported by a Grantin-Aid from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
References [1] G. Binning, H. Rohrer, Sci. Am. 253 (1985) 50. [2] G. Binning, C.F. Quate, Ch. Gerber, Phys. Rev. Lett. 56 (1986) 930. [3] Y. Martin, D. Rugar, H.K. Wickramasinghe, Appl. Phys. Lett. 52 (1988) 244.
ARTICLE IN PRESS 372
M. Shimizu et al. / Journal of Magnetism and Magnetic Materials 282 (2004) 369–372
[4] C.C. Tsuei, J.R. Kirtly, C.C. Chi, L.S. Yu-Jahnes, A. Gupta, T. Shaw, J.Z. Sun, M.B. Ketchen, Phys. Rev. Lett. 73 (1994) 593. [5] M. Johnson, J. Clarke, J. Appl. Phys. 67 (1990) 6141.
[6] T. Kohashi, K. Koike, Jpn. J. Appl. Phys. 40 (2001) 1264. [7] A.M. Chang, H.D. Hallen, L. Harriot, H.F. Hess, H.L. Kao, J. Kwo, R.E. Miller, R. Wolte, J. van der Ziel, T.Y. Chang, Appl. Phys. Lett. 61 (1992) 1974.