Page 65 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 1 BASIC PROPERTIES AND MEASURING METHODS OF NANOPARTICLES
1.12 Magnetic properties If magnetic field charges on paramagnetic sub-
stances, their magnetization would be very little.
Super-magnetism often arises on nano magnetic
Nanoparticles have small volume in the similar range substance. It appears when substance is composed of
to molecule one. Magnetism of not only nanoparticles nano magnetic nanoparticles or magnetic fine particle
but also magnetic molecules appears by interactive exists in metal. Super-magnetic substances would not
effect between magnetic moments [1]. show magnetism without external magnetic field
Electron motion on the atomic nucleus orbit is reg-
ulated by energy, angular momentum and spin because the magnetic moment easily changes the
direction with thermal vibration. It behaves as para-
(atomic magnetic moment). Energy is described by magnetic substance with external magnetic field.
orbit radius around the nucleus. If it has larger energy,
the orbit radius becomes larger. Angular momentum (2) Antiferromagnetism
is a counterpart of integrated intensity. Spin corre- Each spin of magnetic molecule cannot be lined by
sponds to electron rotation. Magnetism of molecule the interaction between spins in antiferromagnetic
depends on both orbital motion (energy and angular substance. Two magnetic ions pinching oxygen ion
momentum) and spin.
are influenced by super-exchange interaction through
p-orbit of oxygen atom. Antiferromagnetic substances
1.12.1 Classification of magnetism are hardly magnetized because all the spins are can-
celled. Then their magnetic susceptibilities become
Many kinds of magnetism appear due to the charac- much smaller.
teristics of interaction between atomic magnetic Herimagnetism arises when atomic spins line in
moments. Magnetic substances are defined as the not only regular direction but also spiral direction. It
substance which has magnetic moment in a magnetic is observed in compounds such as MnO , metals
2
field. Magnetic substances are classified into several such as MnAu and rare earth metal such as Tb, Dy,
2
groups as follows [2]: Ho, Er and Tm. In the case of metal, conduction
electron is magnetized by spin. The magnetization of
1. Feeble magnetism conduction electron would decrease with turning
about electric sign when the distance from the spin
-Diamagnetism
becomes large. This spin interaction with conduction
- Paramagnetism
electron is called RKKY-interaction. Spiral structure
- Super-magnetism [5] that appears in rare earth metal is caused by
2. Antiferromagnetism RKKY-interaction [6–9].
- Antiferromagnetism Metamagnetism is a phenomenon that magnetism of
substance changes from diamagnetic to ferromagnetic
- Herimagnetism
by external magnetic field. For instance, magnetiza-
- Metamagnetism
tion of several compounds such as FeCl and MnAu 2
2
3. Ferromagnetism is proportional to a weak magnetic field. But their
- Parasitic ferromagnetism spins are reversed to line in the same direction and
- Ferrimagnetism then the magnetization suddenly increases at a critical
point of magnetic field.
- Ferromagnetism
(3) Ferromagnetism
(1) Feeble magnetism Generally ferromagnetic substances show sponta-
Feeble magnetism means the substances that are mag- neous magnetization. Spontaneous magnetization is
netized only a little by a magnetic field. In many formed by spin distribution in the ferromagnetic
2
cases, its magnetization I [Wb/m ] is proportional to substance. When external magnetic field acts on the
magnetic field H [A/m] and described as I H. is ferromagnetic substance, this spontaneous magneti-
magnetic susceptibility. If it is described as a ratio to zation change the direction and reach saturated
vacant magnetic permeability , it is called as spe- state. When the external magnetic field is removed,
0
cific magnetic susceptibility [3, 4]. the saturated ferromagnetic substance has residual
Diamagnetism arises when I is caused in the inverse magnetization. Both saturated and residual magne-
direction of H, and magnetic susceptibility is 0. tizations are very important parameters which indi-
Substances that do not have spin such as copper and cate the characteristics of magnetic substance.
organic compounds have diamagnetism. When spins of magnetic molecules line up with a
Substances whose is negative and has an amount slight angle against antiferromagnetic distribution,
2
of 10 10 5 show paramagnetism. The reason of parasitic ferromagnetism raises as imperceptible
weak magnetism is that magnetic substance has a spin spontaneous magnetization [10, 11].
but the spin moves with random vibration when there Ferrimagnetism shows spontaneous magnetization
are magnetic molecular with magnetic moment in it. when spin distribution becomes irregular because
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