OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 17, Iss. 18 — Aug. 31, 2009
  • pp: 16160–16165
« Show journal navigation

A high resolution magneto-optical system for imaging of individual magnetic flux quanta

Daniel Golubchik, Emil Polturak, Gad Koren, and Stephen G. Lipson  »View Author Affiliations


Optics Express, Vol. 17, Issue 18, pp. 16160-16165 (2009)
http://dx.doi.org/10.1364/OE.17.016160


View Full Text Article

Acrobat PDF (514 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

A high-resolution magneto-optical imaging system is described. In this system magneto-optical Kerr effect is utilized for resolving individual flux quanta in a type II superconductor. Using an ultra thin EuSe indicator a spatial resolution of 0.8µm is achieved.

© 2009 Optical Society of America

1. Introduction

Imaging magnetic fields on surfaces is of great importance both in basic science and technology (e.g. magnetic memories, spintronics). It is of particular interest in type II superconductors, where the magnetic field forms isolated vortices, each carrying a quantum of magnetic flux Φ0=2.07×10-15 Wb confined within an area of radius λ, typically ~100 nm. Magnetic imaging methods capable of imaging a single vortex include Electron microscopy [1

1. K. Harada, T. Matsuda, J. Bonevich, M. Igarashi, S. Kondo, G. Rozzi, U. Kawabe, and A. Tonomuko, “Real-time observation of vortex lattices in a superconductor by electron microscopy,” Nature (London) 360, 51–53 (1992). [CrossRef]

], Bitter decoration [2

2. I. V. Grigorieva, “Magnetic flux decoration of type-II superconductors,” Superconductor Science and Technology , 7, 161–177 (1994). [CrossRef]

], scanning SQUID microscope [3

3. Lock See J. R. Kirtley, C. C. Tsuei, J. Z. Sun, C. C. Chi, Yu- Jahnes, A. Gupta, M. Rupp, and M. B. Ketchen, “Symmetry of the order parameter in the high-Tc superconductor YBa2Cu3O7- δ,” Nature (London) 373, 225–228 (1995). [CrossRef]

], Magnetic Force Microscopy [4

4. Z. Deng, E. Yenilmez, J. Leu, J. E. Hoffman, E. W. J. Straver, H. Dai, and K. A. Moler, “Metal-coated carbon nanotube tips for magnetic force microscopy,” Appl. Phys. Lett. 85, 6263–6265 (2004). [CrossRef]

], and Hall Probe Microscopy [5

5. C. W. Hicks, L. Luan, K. A. Moler, E. Zeldov, and H. Shtrikman, “Noise characteristics of 100 nm scale GaAs/AlxGa1-xAs scanning Hall probes,” Appl. Phys. Lett. 90, 133512 (2007). [CrossRef]

]. Some techniques ([1

1. K. Harada, T. Matsuda, J. Bonevich, M. Igarashi, S. Kondo, G. Rozzi, U. Kawabe, and A. Tonomuko, “Real-time observation of vortex lattices in a superconductor by electron microscopy,” Nature (London) 360, 51–53 (1992). [CrossRef]

, 4

4. Z. Deng, E. Yenilmez, J. Leu, J. E. Hoffman, E. W. J. Straver, H. Dai, and K. A. Moler, “Metal-coated carbon nanotube tips for magnetic force microscopy,” Appl. Phys. Lett. 85, 6263–6265 (2004). [CrossRef]

]) have superior spatial and magnetic resolution, with an ability to investigate the internal structure of the vortex. However, high resolution comes at the expense of speed and the maximal area one could image. Magneto-optical imaging (MOI) on the other hand is typically used for rapid imaging of relatively large areas with a lower resolution [6

6. M. R. Koblischka and R. J. Wijngaarden, “Magneto-optical investigations of superconductors,” Supercond. Sci. Technol. 8, 199–214 (1995). [CrossRef]

]. For a review of the different techniques, see [7

7. S. J. Bending, “Local magnetic probes of superconductors,” Adv. Phys. 48, 449–535 (1999). [CrossRef]

, 8

8. R. P. Hübener, Magnetic Flux Structures in Superconductors2nd edition (Springer, Berlin, 2001).

]. The field of view varies from few millimeters at low magnification down to ~100×100µm 2 at maximal resolution. Relatively short measurement times permit investigation of the dynamics of vortex arrays at low fields and allow collection of large amounts of data for statistical analysis. However, resolving individual vortices with magneto-optics is a challenge met so far only by one group[9

9. P. E. Goa, H. Hauglin, A. F. Olsen, M. Baziljevich, and T. H. Johansen, “Magneto-optical imaging setup for single vortex observation,” Rev. Sci. Instrum. 74, 141–146 (2003). [CrossRef]

]. In the following, we present the design and performance of an MOI system with the best resolution achieved so far.

2. Experimental system

Fig. 1. Schematic sketch of the experimental system: (1) Hg 100W light source, (2) Interference filters, (3) Polarizer (extinction ratio 1:10000), (4)Analyzer (extinction ratio 1:10000), (5) Non polarizing beam splitter, (6) Objective, (7)Vacuum windows, (8) Sample holder, (9) Flexible thermal connection, (10) CCD camera, (11) Cold finger, (12) Liquid Helium bath, (13) Vacuum chamber, (14) XYZ manipulator, (15) Manipulator to sample holder coupling, (16) Optical fiber.

The light reflected from the sample passes through a second polarizer oriented at an angle π/2-ϕ relative to the original polarization. Maximal contrast is achieved when ϕ=√e, where e is extinction ratio, namely the ratio of the residual intensity of light measured with the polarizers crossed to the maximum intensity. The contrast in this case is C=θB/√e. The extinction ratio of the system at room temperature is e=4×10-3. When the sample is cooled down the objective is exposed to the low temperature environment and cools by thermal radiation. As a result, thermal strains of the lens degrade the extinction ratio to e=1×10-2. In this case the angle between polarizers should be ϕ⋍5°. Experimentally the contrast doesn’t change significantly in the range ϕ=3-10°. The intensity on the other hand is proportional to ϕ 2. In order to increase the signal to noise ratio as much as possible we used ϕ=10°.

In our system, at the maximal magnification (×50 objective), each pixel of the image covers an area of 0.12×0.12µm 2 of the sample. The total field of view is 110×160µm 2.

3. Results and discussion

An image of a superconductor cooled at two different external magnetic fields shown in Figure 2. The brightness is proportional to the local magnetic field. Each spot represents a single vortex. This figure vividly illustrates the power of the MOI technique where enough individual vortices can be seen to permit the determination of spatial correlations, long and short range order, etc. At Figure 2.b some of the vortices are 1µm apart, approaching our spatial resolution limit, but still can be resolved.

Within the small thickness of MO indicator the magnetic field of a single vortex is localized inside an area much smaller than our optical resolution.

Therefore the image of individual vortex can be approximated by an optical pointspread Airy function [17

17. S. G. Lipson, H. Lipson, and D. S. Tannhauser, Optical physics3rd ed, (Cambridge University Press, 1995).

] I ~ (J 1(kx)/kx)2, where J 1 is a first order Bessel function of the first kind. Figure 3 shows the intensity profile produced by an individual vortex. The intensity is fitted with an Airy function with k=4.4µm -1. Using the Rayleigh criterion, our MO spatial resolution is 0.8µm, which is much better than 1.3µm reported by [9

9. P. E. Goa, H. Hauglin, A. F. Olsen, M. Baziljevich, and T. H. Johansen, “Magneto-optical imaging setup for single vortex observation,” Rev. Sci. Instrum. 74, 141–146 (2003). [CrossRef]

]. Note that the spatial resolution is limited by optical diffraction.

Another example of the power of this technique can be seen in figure 4. Here we show the edge of a dendrite-like formation of a magnetic flux inside the superconductor. Dendrite-like formations are observed at temperatures well below Tc, where magnetic flux penetrates into the sample via a thermo-magnetic instability [18

18. T. H. Johansen, M. Baziljevich, D. V. Shantsev, P. E. Goa, Y. M. Gal pe rin, W. N. Kang, H. J. Kim, E. M. Choi, M.-S. Kim, and S. I. Lee, “Dendritic magnetic instability in superconducting MgB2 films,” Europhys. Lett. 59, 599–606 (2002) [CrossRef]

]. This phenomenon was extensively investigated using conventional magneto-optics (see [19

19. T.H. Johansen, M. Baziljevich, D.V. Shantsev, P.E. Goa, Y.M. Galperin, W.N. Kang, H.J. Kim, E.M. Choi, M. S. Kim, and S.I. Lee, “Dendritic flux patterns in MgB2 films,” Supercond. Sci. Technol. 14, 726–729 (2001). [CrossRef]

]). In this case, we see a magnetic structure with a high density of positive flux (bright region) penetrates into a sample having an initially uniform distributed negative magnetic flux (dark region). With our high resolution, individual vortices can be distinguished at the front edge of this structure. Notice that flux lines of different polarities (bright and dark spots) are separated by an annihilation zone where the density of the vortices is low. Such images allow us to study annihilation dynamics.

Fig. 2. MO images of superconducting Nb film under external magnetic fields. The field is: (a) 0.4mT, (b) 1.2mT. The scale bar represents 5µm. Each bright spot represents a single vortex. At these low fields, the positions of individual vortices are determined by local disorder rather then by vortex-vortex interaction.
Fig. 3. Intensity profile across a single vortex. The line is a fit to an Airy function.
Fig. 4. Edge of a dendrite-like magnetic structure pinned in a superconductor. To produce this structure, the superconductor was first cooled through Tc in the presence of a magnetic field (-4mT) and then the field was reduced to zero. The inset shows a low resolution image of a similar structure. The scale bar in the inset represents 100µm.

4. Conclusion

In conclusion, we have developed a high resolution MO imaging system which can be used for studies of vortex arrays on spatial scales ranging from single flux quanta up to structures containing thousands of vortices. Work is already underway to study out of equilibrium vortex formation and spatial correlation of the emerging vortex arrays.

Acknowledgments

We thank E. Buks for sharing with us his Nb film deposition system. We thank S. Hoida, L. Iomin and O. Shtempluk for technical assistance. This work was supported by Israel Science Foundation and by the Technion Fund for Research.

References and links

1.

K. Harada, T. Matsuda, J. Bonevich, M. Igarashi, S. Kondo, G. Rozzi, U. Kawabe, and A. Tonomuko, “Real-time observation of vortex lattices in a superconductor by electron microscopy,” Nature (London) 360, 51–53 (1992). [CrossRef]

2.

I. V. Grigorieva, “Magnetic flux decoration of type-II superconductors,” Superconductor Science and Technology , 7, 161–177 (1994). [CrossRef]

3.

Lock See J. R. Kirtley, C. C. Tsuei, J. Z. Sun, C. C. Chi, Yu- Jahnes, A. Gupta, M. Rupp, and M. B. Ketchen, “Symmetry of the order parameter in the high-Tc superconductor YBa2Cu3O7- δ,” Nature (London) 373, 225–228 (1995). [CrossRef]

4.

Z. Deng, E. Yenilmez, J. Leu, J. E. Hoffman, E. W. J. Straver, H. Dai, and K. A. Moler, “Metal-coated carbon nanotube tips for magnetic force microscopy,” Appl. Phys. Lett. 85, 6263–6265 (2004). [CrossRef]

5.

C. W. Hicks, L. Luan, K. A. Moler, E. Zeldov, and H. Shtrikman, “Noise characteristics of 100 nm scale GaAs/AlxGa1-xAs scanning Hall probes,” Appl. Phys. Lett. 90, 133512 (2007). [CrossRef]

6.

M. R. Koblischka and R. J. Wijngaarden, “Magneto-optical investigations of superconductors,” Supercond. Sci. Technol. 8, 199–214 (1995). [CrossRef]

7.

S. J. Bending, “Local magnetic probes of superconductors,” Adv. Phys. 48, 449–535 (1999). [CrossRef]

8.

R. P. Hübener, Magnetic Flux Structures in Superconductors2nd edition (Springer, Berlin, 2001).

9.

P. E. Goa, H. Hauglin, A. F. Olsen, M. Baziljevich, and T. H. Johansen, “Magneto-optical imaging setup for single vortex observation,” Rev. Sci. Instrum. 74, 141–146 (2003). [CrossRef]

10.

G. Carneiro and E. H. Brandt, “Vortex lines in films: Fields and interactions,” Phys. Rev. B 61, 6370–6376 (2000). [CrossRef]

11.

A. Laraoui, M. Albrecht, and J. Y. Bigot,“Femtosecond magneto-optical Kerr microscopy,” Opt. Lett. 32, 936–938 (2007). [CrossRef] [PubMed]

12.

M. Elazar, M. Sahaf, L. Szapiro, D. Cheskis, and S. Bar-Ad, “Single-pulse magneto-optic microscopy: a new tool for studying optically induced magnetization reversals,” Opt. Lett. 33, 2734–2736 (2008). [CrossRef] [PubMed]

13.

J. Schoenes and P. Wachter, “Magnetooptic Spectroscopy of EuS, EuSe, and EuTe,” Trans. Magnetic 12, 81–85 (1976). [CrossRef]

14.

Th. Schuster, M. R. Koblischka, B. Ludescher, N. Moser, and H. Kronmuller, “EuSe as magneto-optical active coating for use with the high resolution Faraday effect,” Cryogenics 31, 811–816 (1991). [CrossRef]

15.

C. R. Reisin and S. G. Lipson, “Intermediate-state structures of type-I superconductors,” Phys. Rev. B , 61, 4251–4258 (2000). [CrossRef]

16.

B. Abdo, E. Segev, O. Shtempluck, and E. Buks, “Nonlinear Coupling in Nb/NbN Superconducting Microwave Resonators,” arXiv:cond-mat/0501236 v1, (2005).

17.

S. G. Lipson, H. Lipson, and D. S. Tannhauser, Optical physics3rd ed, (Cambridge University Press, 1995).

18.

T. H. Johansen, M. Baziljevich, D. V. Shantsev, P. E. Goa, Y. M. Gal pe rin, W. N. Kang, H. J. Kim, E. M. Choi, M.-S. Kim, and S. I. Lee, “Dendritic magnetic instability in superconducting MgB2 films,” Europhys. Lett. 59, 599–606 (2002) [CrossRef]

19.

T.H. Johansen, M. Baziljevich, D.V. Shantsev, P.E. Goa, Y.M. Galperin, W.N. Kang, H.J. Kim, E.M. Choi, M. S. Kim, and S.I. Lee, “Dendritic flux patterns in MgB2 films,” Supercond. Sci. Technol. 14, 726–729 (2001). [CrossRef]

OCIS Codes
(120.4820) Instrumentation, measurement, and metrology : Optical systems
(190.3270) Nonlinear optics : Kerr effect
(210.3810) Optical data storage : Magneto-optic systems

ToC Category:
Instrumentation, Measurement, and Metrology

History
Original Manuscript: June 26, 2009
Revised Manuscript: August 10, 2009
Manuscript Accepted: August 17, 2009
Published: August 26, 2009

Virtual Issues
August 26, 2009 Spotlight on Optics

Citation
Daniel Golubchik, Emil Polturak, Gad Koren, and Stephen G. Lipson, "A high resolution magneto-optical system for imaging of individual magnetic flux quanta," Opt. Express 17, 16160-16165 (2009)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-17-18-16160


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. K. Harada, T. Matsuda, J. Bonevich, M. Igarashi, S. Kondo, G. Rozzi, U. Kawabe, and A. Tonomuko, "Real-time observation of vortex lattices in a superconductor by electron microscopy," Nature (London) 360, 51-53 (1992). [CrossRef]
  2. I. V. Grigorieva, "Magnetic flux decoration of type-II superconductors," Supercond. Sci. Technol. 7, 161-177 (1994). [CrossRef]
  3. J. R. Kirtley, C. C. Tsuei, J. Z. Sun, C. C. Chi, Lock See Yu-Jahnes, A. Gupta, M. Rupp, and M. B. Ketchen, "Symmetry of the order parameter in the high-Tc superconductor YBa2Cu3O7- ™," Nature (London) 373, 225-228 (1995). [CrossRef]
  4. Z. Deng, E. Yenilmez, J. Leu, J. E. Hoffman, E. W. J. Straver, H. Dai, and K. A. Moler, "Metal-coated carbon nanotube tips for magnetic force microscopy," Appl. Phys. Lett. 85, 6263-6265 (2004). [CrossRef]
  5. C. W. Hicks, L. Luan, K. A. Moler, E. Zeldov, and H. Shtrikman, "Noise characteristics of 100 nm scale GaAs/AlxGa1?xAs scanning Hall probes," Appl. Phys. Lett. 90, 133512 (2007). [CrossRef]
  6. M. R. Koblischka and R. J. Wijngaarden, "Magneto-optical investigations of superconductors," Supercond. Sci. Technol. 8,199-214 (1995). [CrossRef]
  7. S. J. Bending, "Local magnetic probes of superconductors," Adv. Phys. 48, 449-535 (1999). [CrossRef]
  8. R. P. Hubener, Magnetic Flux Structures in Superconductors 2nd edition (Springer, Berlin, 2001).
  9. P. E. Goa, H. Hauglin, A. F. Olsen, M. Baziljevich, and T. H. Johansen, "Magneto-optical imaging setup for single vortex observation," Rev. Sci. Instrum. 74, 141-146 (2003). [CrossRef]
  10. G. Carneiro and E. H. Brandt, "Vortex lines in films: Fields and interactions," Phys. Rev. B 61, 6370-6376 (2000). [CrossRef]
  11. A. Laraoui, M. Albrecht, and J. Y. Bigot,"Femtosecond magneto-optical Kerr microscopy," Opt. Lett. 32, 936-938 (2007). [CrossRef] [PubMed]
  12. M. Elazar, M. Sahaf, L. Szapiro, D. Cheskis, and S. Bar-Ad, "Single-pulse magneto-optic microscopy: a new tool for studying optically induced magnetization reversals," Opt. Lett. 33, 2734-2736 (2008). [CrossRef] [PubMed]
  13. J. Schoenes and P. Wachter, "Magnetooptic Spectroscopy of EuS, EuSe, and EuTe," Trans. Magnetic 12, 81-85 (1976). [CrossRef]
  14. Th. Schuster, M. R. Koblischka, B. Ludescher, N. Moser, and H. Kronmuller, "EuSe as magneto-optical active coating for use with the high resolution Faraday effect," Cryogenics 31, 811-816 (1991). [CrossRef]
  15. C. R. Reisin and S. G. Lipson, "Intermediate-state structures of type-I superconductors," Phys. Rev. B 61, 4251-4258 (2000). [CrossRef]
  16. B. Abdo, E. Segev, O. Shtempluck, and E. Buks, "Nonlinear Coupling in Nb/NbN Superconducting Microwave Resonators," arXiv:cond-mat/0501236 v1, (2005).
  17. S. G. Lipson, H. Lipson and D. S. Tannhauser, Optical physics 3rd ed, (Cambridge University Press, 1995).
  18. T. H. Johansen, M. Baziljevich, D. V. Shantsev, P. E. Goa, Y. M. Gal pe rin, W. N. Kang, H. J. Kim, E. M. Choi, M.-S. Kim, and S. I. Lee, "Dendritic magnetic instability in superconducting MgB2 films," Europhys. Lett. 59, 599-606 (2002) [CrossRef]
  19. T. H. Johansen, M. Baziljevich, D. V. Shantsev, P.E. Goa, Y. M. Galperin, W. N. Kang, H. J. Kim, E. M. Choi, M. S. Kim, and S. I. Lee, "Dendritic flux patterns in MgB2 films," Supercond. Sci. Technol. 14, 726-729 (2001). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

Figures

Fig. 1. Fig. 2. Fig. 3.
 
Fig. 4.
 

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited