CHEM 122L General Chemistry Laboratory Revision 1.2 The Synthesis of a Ferrofluid and a Magnetic Garnet To learn about the different types of magnetic solids. To learn about magnetic fluids. To learn about Rare Earth chemistry. In this laboratory exercise we will synthesis a Ferrofluid and a Magnetic Garnet. The ferrofluid is an aqueous colloidal suspension of Magnetite particles that will exhibit a "spiking" effect in the presence of a magnetic field. The garnet is a Rare Earth solid solution of Yttrium and Gadolinium mixed with Iron Oxide which exhibits a zero magnetization below its Currie Temperature. The behavior of both these materials can be explained by examining the spins of the electrons of the cations that comprise the Magnetite and the garnet. Most of the substances we experience in everyday life are composed of compounds or elements that are diamagnetic and exhibit a property called diamagnetism; the property whereby they are very weakly repelled by a magnetic field. Diamagnetic materials are those that are generally considered to be "non-magnetic", although this is a bit qualitative. These substances have no unpaired electrons. For example, metallic Calcium has an electron configuration of: Ca = [Ar] 4s 2 All of its core and valence shell electrons are "paired" according to the Pauli Exclusion Principle with anti-parallel spins: In this configuration the magnetic moments of the electrons effectively cancel. Diamagnetism is then a quantum mechanical effect associated with the orbital motion of electrons within an atom. On the other hand, the Ferric Ion has an electron configuration of: Fe 3+ = [Ar] 3d 5 giving it 5 unpaired electrons, distributed in the d-orbitals according to Hund's Rule:
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CHEM 122L
General Chemistry Laboratory
Revision 1.2
The Synthesis of a Ferrofluid and a Magnetic Garnet
To learn about the different types of magnetic solids.
To learn about magnetic fluids.
To learn about Rare Earth chemistry.
In this laboratory exercise we will synthesis a Ferrofluid and a Magnetic Garnet. The ferrofluid
is an aqueous colloidal suspension of Magnetite particles that will exhibit a "spiking" effect in
the presence of a magnetic field. The garnet is a Rare Earth solid solution of Yttrium and
Gadolinium mixed with Iron Oxide which exhibits a zero magnetization below its Currie
Temperature. The behavior of both these materials can be explained by examining the spins of
the electrons of the cations that comprise the Magnetite and the garnet.
Most of the substances we experience in everyday life are composed of compounds or elements
that are diamagnetic and exhibit a property called diamagnetism; the property whereby they are
very weakly repelled by a magnetic field. Diamagnetic materials are those that are generally
considered to be "non-magnetic", although this is a bit qualitative. These substances have no
unpaired electrons. For example, metallic Calcium has an electron configuration of:
Ca = [Ar] 4s2
All of its core and valence shell electrons are "paired" according to the Pauli Exclusion Principle
with anti-parallel spins:
In this configuration the magnetic moments of the electrons effectively cancel. Diamagnetism is
then a quantum mechanical effect associated with the orbital motion of electrons within an atom.
On the other hand, the Ferric Ion has an electron configuration of:
Fe3+
= [Ar] 3d5
giving it 5 unpaired electrons, distributed in the d-orbitals according to Hund's Rule:
P a g e | 2
Fe3+
is therefore paramagnetic; it exhibits paramagnetism due to the "unpaired" electrons and
their aligned magnetic moments. Paramagnetic substances are drawn very strongly into a
magnetic field. The more unpaired electrons in a species, the stronger the paramagnetism.
As an aside, molecular Oxygen (O2) is paramagnetic. It has two unpaired electrons. This can be
seen by examining the Molecular Orbital energy diagram for its valence shell electrons.
This means liquid Oxygen will be drawn into a magnetic field and held in place. (Why will we
not see this with gaseous Oxygen?) This is demonstrated very nicely in the following You Tube
viedeo:
http://www.youtube.com/watch?v=Isd9IEnR4bw
Due to thermal motion the net spin of paramagnetic atoms or ions (5 unpaired electron spins =
for the Fe3+
cation) are randomly oriented to each other.
Rare Earth Iron Garnets
Margret J. Geselbracht, et al
Journal of Chemical Education (1994)
In Ferromagnetic materials, the net spins tend to align themselves in regions called Magnetic
Domains. These materials are what we think of as permanent magnets. When subjected to a
magnetic field (H), the net spins in all the domains align themselves in the same direction with
the field. (This is not exactly true, but the overall picture is close enough to the truth that we can
consider it to be correct.)
P a g e | 3
Rare Earth Iron Garnets
Margret J. Geselbracht, et al
Journal of Chemical Education (1994)
Below a material's Curie Temperature, the substance can retain a configuration whereby all the
net spins within all the domains are aligned and the material has a permanent Magnetic Moment,