Magnetic Imaging

METALS

Our goal is to develop a real-time magnetic domain imaging system 

and apply it to technologically important systems, including datastorage and permanent magnets with increased energy products, in 

order to test and publicize its unique capabilities. In this project we 

will develop methods to visualize magnetization reversal processes 

to explain the mechanism and ramifications of exchange interaction 

on the remagnetization processes in composite magnetic materials 

comprised of species with dissimilar bulk magnetic characteristics.

Objective

Impact and Customers

• In collaboration with the Russian Academy of Sciences (Moscow), the advanced Magneto-Optic Indicator Film 

technique (MOIF) was developed to image magnetic spins and domain structures in real time. Other collaborators 

include the Johns Hopkins University and Chang Won University (S. Korea). 

• The technique is now used in many laboratories around the world for imaging flux penetration in superconductors; 

for high TC superconductors, it is the “method of choice.” Acceptance by manufacturers of miniature magnetic 

devices such as the newer generation of magnetic read heads and field sensors has been slower due to 

unavailability of enough imaging films. 

• Using the MOIF technique we have been able to make several unique and technologically important measurements, 

including the findings that the remagnetization behavior can “differ” for different sides of the hysteresis loop in 

technologically-important “exchange-biased” films, and proving magnetic spin rotation in magnetic “exchange 

springs.”

Approach

Materials Science and Engineering Laboratory

Advanced magnetic devices and storage media will rely on ultrathin ferromagnetic films; since such films are quasi two-dimensional 

magnets, they can have strong perpendicular magnetic anisotropy (PMA). 

Optimization of future materials, including improved yields, requires 

the ability to measure film interactions. The advanced magneto-optical 

indicator film (MOIF) technique is a particularly appropriate tool to obtain 

such information.

This technique uses a Bi-substituted yttrium iron garnet film with in-plane 

anisotropy, placed on top of a specimen to be analyzed. This enables 

the observation of the magnetic stray fields above the specimen through 

the magneto-optical double Faraday effect of the garnet film. This optical 

image of the stray magnetic fields is observed by polarized light optical 

microscopy. A digital difference technique is used for quantitative analysis 

of the magneto-optical images. 

Advantages of the MOIF method: 

• Real time visualization of magnetization dynamics. 

• Any magnetic material can be investigated, and only magnetic information is observed. 

• Quantitative 

• Observations over a wide temperature range.

• It is simple in operation, and inexpensive to construct. 

855-11-13b
Materials Science and Engineering Laboratory

Developing new magnetic materials 

for magnetic storage devices 

requires a deep understanding of the 

remagnetization processes. To help 

the industry in such an important task, 

NIST is using the advanced MagnetoOptical Imaging technique to study 

magnetization reversal processes in 

magnetic materials with perpendicular 

magnetic anisotropy, such as artificial 

nanostructures consisting of two or 

more materials with drastically different 

magnetic characteristics. This study 

by the Magneto-Optical Indicator Film 

technique (MOIF) provided visualization 

of the magnetization reversal in a 

bilayer consisting of a continuous 30 nm 

thick Ni77Fe14Mo5Cu4 soft ferromagnetic 

(FM) film covered by a 10 nm-thick, 

patterned square grid (110 μm wide 

squares with 10 μm wide grid strips) of 

antiferromagnetic (AFM) FeMn.

We have discovered that the 

antiferromagnet not only changes the 

properties of the FM regions immediately 

underneath it, but despite the large 

pattern period, also drastically affects the 

remagnetization behavior in the adjacent 

uncovered parts of the ferromagnet. 

Specifically, we demonstrated patterncontrolled nucleation of domain walls 

and an overall asymmetry in the 

reversal behavior of the uncovered FM 

film when the polarity of the in-plane 

field is reversed. These data show 

an unexpectedly long-range lateral 

influence on thin-film magnetization 

reversal by a rectangular array of FeMn 

pinning films.

We consider these results to be a 

major advance in understanding the 

remagnetization processes of patterned 

magnetic media, and we expect that 

our results will be used by the recording 

industry to develop magnetic materials 

for practical applications in perpendicular 

magnetic recording, and by scientists to 

understand the nature of the exchange 

interactions at the interface between a 

ferromagnet and an antiferromagnet. 

This program is important because 

ultra-thin patterned ferromagnetic 

films, especially those with strong 

perpendicular magnetic anisotropy 

(PMS), are candidates for use by the 

magnetic recording industry to achieve 

very high density storage. Therefore, it is 

crucial that the industry know the distance 

to which magnetic exchange bias effects 

between a FM and an AFM extend in 

the ferromagnet; conventional wisdom 

would not have led to expectations of tens 

of micrometers as the extent of the effect.

Accomplishments

Robert D. Shull

Valerian I. Nikitenko

Alexander J. Shapiro

(Metallurgy Division)

(301) 975-5970

alexander.shapiro@nist.gov

www.nist.gov/metallurgy

Learn More

Kabanov YP, Nikitenko VI, Egelhoff, Jr. WF, Shapiro A and Shull R In-plane Bias in a 

Patterned Ferromagnetic/Antiferromagnetic Bilayer Phys.Rev. B, (2008 in press)

Iunin YL, Kabanov YP, Nikitento VI, Cheng XM, Clarke D, Tretiakov OA, Tchernyshyov 

O, Shapiro AJ, Shull RD and Chien CL Asymmetric Domain Nucleation and Unusual 

Magnetization Reversal in Ultrathin Co films with Perpendicular Anisotropy Phys. Rev. 

Lett., 98 (11) 117204 (2007)

Gornakov VS, Kabanov YP and Tikhomirov OA Experimental Study of the Microscopic 

Mechanisms of Magnetization Reversal in FeNi/FeMn Exchange-biased Ferromagnet/

Antiferromagnet Polycrystalline Bilayers Phys. Rev., 73 (18) 184428 (2006)

Cheng XM, Nikitenko VI and Shapiro AJ Unusual Magnetization Reversal in [Co/Pt](4) 

Multilayers with Perpendicular Anisotropy JAP, 99 (8) 08C905 (2006)

MOIF image shows the asymmetry of the domain 

structure dynamics during magnetization reversals 

in opposite directions. 

Forward branch of the hysteresis loop: 

(a) μo

H=1.32 mT, (b) μoH=1.38 mT,

(c) μoH=1.62 mT.

Backward branch: 

(d) μoH=0, (e) μoH=-0.84 mT, (f) μoH=-0.88 mT.

Publications