Real-Time Magneto-Optical Imaging of Vortex Lattice

Real-time magneto-optical imaging of vortices in superconducting NbSe2
P.-E. Goa et al. SuST 14, 729 (2001)
Manipulation of vortices by magnetic domain walls
P.-E. Goa et al. APL 82, 79 (2003)
Magneto-optical imaging setup for single vortex observation
P.-E. Goa et al. RSI 74, 141 (2003)
Magneto-optic imaging of single vortex dynamics in NbSe2 crystals
M. Baziljevich et al. Adv. Sci. Tech. 38, 377 (2003)
Single vortices observed as they enter NbSe2
A. A. F. Olsen et al., Physica C 408-410, 537 (2004)
Interaction between superconducting vortices and Bloch wall in ferrite garnet film
J. I. Vestgarden et al., Phys. Rev. Lett. 98, 117002 (2007)

Resolving Individual Vortices

The magneto-optical imaging technique has been improved to enable observation of magnetic vortices in type-II superconductors. The main advantage of the method is its high temporal resolution combined with the applicability to any superconducting sample with a flat surface.

Vortex lattice in NbSe2 superconductor, H=3 Oe Abrikosov lattice in superconductor, H=7 Oe

Magneto-optical images of vortices in a NbSe2 superconducting crystal at 4.3 K after cooling in magnetic field of 3 and 7 Oe.  PDF

This image is used in the Illustrated Presentation for the Nobel Prize in Physics 2003. See also Gallery of Abrikosov lattices obtained by different techniques.

 


Vortex dynamics

Dynamics of Vortices in superconductor  

The image shows the change in flux distribution over a 1 sec. time interval after a 4 mOe increase in the applied field. Dark and bright spots represent initial and final vortex positions, respectively. Medium brightness corresponds to unchanged flux distribution, indicating stationary vortices. The inset shows a close up of four vortex jumps. Arrows indicate the direction of vortex motion.  PDF

 


Movies of vortex penetration

Initial vortex distribution is a result of cooling in a low magnetic field. Then, the applied field increases and new vortices slowly enter the crystal from the edge (located at the top). At larger fields the surface barrier is broken and many vortices penetrate very fast. Movie window: 25x35 microns, sample: NbSe2 crystal.

PDF
 
Initial vortex distribution is a result of cooling in a low negative field (vortices are dark). Then, a positive field is applied, and the vortices exit the crystal slowly. When there is almost no vortices near the edge, the vortices of the opposite polarity (bright spots) enter the sample. Movie window: 25x25 microns, sample: NbSe2 crystal.

See also movies showing manipulation vortices with domain wall and difference movies

 


MO imaging setup with single vortex resolution


 
Principle of magneto-optical technique  

Principle of MO-imaging

Maxima of the magnetic field from vortices in a superconducting sample (SC) give maxima in the Faraday rotation QF of incoming plane polarized light in a ferrite garnet layer (FGF) near the sample. Vortices appear as bright spots when imaged using a crossed polarizer(P)/analyser(A) setting. Details of the single-vortex imaging setup are given in  PDF

More about magneto-optics: MO imaging of Superconductors page.


Other methods for vortex visualization:

  • Bitter decoration
  • Scanning magnetic probes
  • Lorentz microscopy
  • Scanning tunneling microscopy

    to view more vortex images visit Gallery of Abrikosov Lattices

Advantages of MO imaging:

  • High temporal resolution
  • Applicability to any superconducting sample with a flat surface
  • Simplicity of imaging setup

 


Interaction between Individual Vortices and a Bloch Wall

The domain wall can repel or attract vortices:


Domain wall in magneto-optical film
 

Interaction between a Bloch wall in a ferrite-garnet film and a vortex in a superconductor is analyzed in the London approximation. Equilibrium distribution of vortices formed around the Bloch wall is calculated.

Our model can reproduce a counter-intuitive attraction observed between vortices and a Bloch wall having the opposite polarity. It is explained by magnetic charges appearing due to discontinuity of the in-plane magnetization across the wall.

Published (theory+experiment):
Phys.Rev.Lett 2007

See also theory for non-charged wall:
PRB-2002 (thick SC), PRB-2002 (thin SC)

MO images showing an enhanced vortex density around a Bloch wall

domain wall and vortices in superconductor
NbSe2. Zero-field cooling. Many vortices (white spots) are seen around two segments of a zigzag domain wall (black lines)
flux quanta remain pinned
The domain wall has been removed


 Manipulation of vortices using a Bloch wall

 

Manipulating flux quanta in superconductor with a Bloch wall   Appl. Phys. Lett. 82, 79 (2003)   PDF

A moving wall can grab vortices. Depending on the ratio between the interaction and the pinning force, the wall can serve as vortex comb (vortices get tilted) or vortex shovel (vortices get depinned). On the images and movie below, a sweep of the wall creates a vortex-free gap at the turning point.  PDF

Tunable and movable nanomagnets can serve as vortex manipulators.

 

vortex lattice after field-cooling
Low-field cooling
manipulating vortices with domain wall
After the wall has been moved in, and then out.

Movie of the domain wall pushing vortices
 

See also: Domain Wall Tip for Manipulation of Magnetic Particles, Phys Rev Lett. 2003


 

Published Feb. 2, 2011 10:19 PM - Last modified Jan. 13, 2012 3:32 PM