Study of morphology and crystalline size of powder materials
P. Roupcová1, 2, Schneeweiss2
1Central
European Institute of Technology,
2Institute of Physics of Materials, Academy of Sciences of Czech
Republic v.v.i., Zizkova
22, 616 62
roupcova@ipm.cz
The superparamagnetism is one of material properties strongly
depended on crystalline size [1]. The grains of magnetic material are occupied
of several magnetic domains, regions with uniform magnetization. The structure
of magnetic domains is responsible for the magnetic behavior
of ferromagnetic materials. Magnetic domains are separated by domain walls.
Grain boundaries as well as particle surface become the domain walls in
magnetic material. The grains in materials with the extremely small crystals or
particles (nanomaterials) are occupied by single
domain and lost its ferromagnetic properties and become superparamagnetic.
Even thermal fluctuation cause random magnetization of this material.
Common
techniques of characterization nanomaterials (nanoparticles) are electron microscopy (TEM), atomic force
microscopy, and X-ray diffraction etc. Each of this method determined the
particle size, shape, morphology by different way. The information about the
shape and size of macromolecules, characteristic distances of partially ordered
materials, pore sizes are possibly obtained from small angle X-ray scattering
method (SAXS) and ultra small angle X-ray scattering (USAXS).
The SAXS
analysis was used in comparison with common technique as well as magnetic
measurement from determination of crystalline size (particle size) of various nanocrystalline materials: 1. Commercial ferryhydride without nanosized
particles. 2. Commercial nanocrystalline magnetite
with particle size 50 nm, which is guaranteed by
producer. 3. Ferrihydride and iron (II-III) oxide
self prepared.
The both
commercial samples are magnetic and by mean TEM study are described like big
well rounded particles. The synthesized samples are determined like
non-magnetic and TEM shows the cluster of smaller objects like nanosized particles and particles embedded in amorphous
matrix. The commercial ferrihydride was out of range
of SAXS measurement and magnetite contains 100 nm particles. The size of
synthesized samples 5 nm (ferryhydride) and 2 nm
(iron (II-III) oxide) determined by SAXS. Those results are different from the
results obtained from TEM and XRD.
1. Wikipedia source, in Superparramagnetism: Introduction, Effect of a Magnetic Field, Applications, and More, edited by Alez Gaby (USA), 2013, pp. 33-50.