Increasing the Sensitivity and Resolution of Magnetic-Force
Choosing the Right Probe
Scanner with No Magnetic Parts
High Temperature Samples
Co. was established in 1991 with the purpose to apply all accumulated
experience and knowledge in the field of nanotechnology to supply researchers
with the instruments suitable to solve any possible task laying in nanometer
scale dimensions. The company NT-MDT was
founded in Zelenograd - the center of Russian Microelectronics. The products
development are based on the combination of the MEMS technology, power of modern
software, use of high-end microelectronic components and precision mechanical
parts. As a commercial enterprise NT-MDT Co.
exists from 1993.
Nowadays the most promising fields of nanotechnology investigations is
nano-scaled objects local magnetization measuring. Investigation of ultra thin
magnetic films will make it possible to increase storage devices capacity
tenfold; spintronics elements creation will lead to the development of
fundamentally new computes with "read/write/save" processes carried out on one
single chip, magnetostriction could be useful for nanoelectronic devices
Magnetic-force microscopy allows visualizing and manipulating the
magnetization of tens nanometers resolution.
There are six essentials of high-quality MFM:
1. increased sensitivity due to vacuum environment
2. proper choice of the probe
3. scanner with no magnetic parts (external field does not obstruct the imaging)
4. accurate external field application
5. many-pass compensation of electrostatic and other influences
6. precise temperature changing during MFM measurements
Increasing the Sensitivity and Resolution of Magnetic-Force Microscopy
There are several ways to increase sensitivity and resolution of
magnetic-force microscopy. The easiest one is placing the measuring system
(sample, scanner and registration system) in the low vacuum environment. For
example, NTEGRA® Aura produces 10-2 torr vacuum which is
enough for tenfold growth of the phase contrast in the two-pass dynamic MFM. But
in this case, the "signal/noise" ratio gains fivefold. The high vacuum
(up to 10-6 torr) allows to increase sensitivity greater, but
comparing to the low vacuum the difference is insignificant.
Figure 1. MFM images of hard disk surface obtained in
ambient air and in vacuum. Both images are of 1x1 µm
Figure 2. Magnetic domain structure of ultra thin cobalt
film (1.6 µm) 4.5 x 4.5 µm. The samples provided by Dr. A. Maziewski,
Uniwersytet w Bialymstoku, Poland
Choosing the Right Probe
Probe quality is another important factor that affects the resolution and
sensitivity of MFM. The tip magnetic coating should be of suitable thickness for
tip could "feel" the sample's magnetic attraction. But at the same time the tip
should be sharp enough to provide high spatial resolution. NT-MDT
silicon probes with CoCr magnetic coating of the tip for magnetic measuring.
Cr protects the magnetic layer from the oxidation. The thickness of the coating
is 30-40 nm.
Scanner with No Magnetic Parts
For the investigation of some magnetic effects it is necessary to apply
external magnetic field to the sample. Usually, it causes certain difficulties
as the regular SPM integrates some details that could be magnetized. As the
result, any external field measurements lead to the distortion of AFM image.
This problem was solved by NT-MDT Co. Its' first device for the magnetic measurements
(1998) had scanner of special design with no magnetic parts.
But today the Company offers brand new equipment - NTEGRA
nanolaboratory platform - with measuring head and base unit made of
non-magnetic materials. That allows to avoid the probe shift while switching
on/off the magnetic field. The scanner is equipped with close loop control
sensors that carry out piezoceramics shift correction and provide exclusively
precise probe positioning.
External Field Application
The external magnetic field could by applied in parallel and perpendicular
way to scan surface. The NTEGRA nanolaboratory's functionality allows to apply the
external magnetic field up to +/-0.2 T in-plain the surface and +/-0.02 T in
perpendicular way (vertical field).
with the longitudinal magnetic field generator
with transverse magnetic field generator
Figure 3. SPM system for measurements in the external
magnetic field on the NTEGRA platform basis
The longitudinal magnetic field generator is intended for the creation of
magnetic field orientated in-plain of the sample. The generator consists of
exciting coil with magnetic wires. The Hall detector with scale range up to 2
kgauss is installed at one of the wires poles in order for measuring the
magnetic field value.
The vertical magnetic field generator is intended for the creation of
magnetic field normal to the flat of the sample. It consists of exciting coil
with build-in Hall detector with scale range of 500 gauss, and a sample
Figure 4. Film of yttrium-ferrous garnet in the presence
of vertical magnetic field. The images of the same part of the surface 90 ? 90
µm. The samples are provided by prof. F.V.Lisovskiy, Radioelectronic Institute,
There are several ways to carry out the compensation of electrostatic and
topography influence, which are presented in Figue 5.
Figure 5. The scheme of three-pass magnetic measurement
of nanoelectronic element
For samples possessing any electrostatic potential several passes should be
performed in one session. On the scheme is an experiment with magnetization of
- 1st pass shows topography;
- 2nd pass shows surface potential with topography influence compensated;
- 3rd pass shows magnetization with both electrostatic potential and
MFM of High Temperature Samples
Sample temperature can be changed during the MFM.
Figure 6. MFM images of the cobalt monocrystal with
uniaxial anisotropy. Phase transition occurs when temperature increases. Images
obtained from the same area, 14 x 40 µm. Sample courtesy of Prof. A.G.
Pastushenkov, Tver University, Russia.
For more information on this source please visit NT-MDT