MadSci Network: Physics

Re: Magnetism

Date: Thu Jun 25 06:32:03 1998
Posted By: Moataz Attallah, Undergraduate, Mechanical Engineering, American University in Cairo
Area of science: Physics
ID: 894559966.Ph

The solution:

Generally speaking, elements and even compounds are divided into three 

Before going into details, there is a theory in chemistry called quantum 
numbers. This theory explains that the electrons are not at rest, but they 
are rotating and spinning in their atomic orbitals. This spin causes a 
magnetic field. This magnetic field is manifested only if the electron is 
not paired.
(It is well known that the old theory that claimed that the electrons 
rotate in circular paths is no longer valid. The new theories says that 
the electrons exist in so called orbitals, which is a space that can 
contain up to 2 electrons. If the one electron exists, the magnetic 
properties will be manifested.)

Returning back to our questions, the first category is for the elements or 
compounds that show some magnetic properties under certain conditions. 
These materials have unbalanced (unpaired) electron(s) in their orbitals. 
These unpaired electrons spin, and their spinning creates magnetic fields. 
Each molecule, hence, forms a magnet. Thus if a magnetic field is applied 
to  these molecular magnets, they will arrange themselves and align to 
increase this effect. This type of magnetism is far weaker than the one 
due to Iron and some other compounds. 
Experimentally, paramagnetic property was found to directly proportional 
to the applied magnetic field, and inversely proportional to the 
temperature (Curie's law). There is a famous example in nearly all Physics 
and Chemistry textbooks showing liquid oxygen being poured between 
magnetic poles; oxygen is seen being attracted to the poles.  

The other type is diamagnetism. These are materials that have their 
electrons paired in their orbitals, thus their magnetic effect cancels 
out. However, if a magnetic field is applied to such a material, the 
fields in the atom will be disturbed causing a weak magnetic field to 
appear, which is far weaker than the one due to paramagnets.

The last type is ferromagnetism. Iron, Cobalt, gadolinium, dysprosium, and 
Nickel show ferromagnetic properties. These are the materials used to 
fabricate permanent magnets. In addition to the unpaired electrons, these 
materials have other magnetic properties described by the Domain theory. 
This theory proposes that these materials contain microscopic regions 
called domains, within which the magnetic fields due to atoms are aligned. 
Their volumes is about 10E-12 to 10E-8 cubic meters. Under normal 
conditions, domains are randomly oriented, and they have no magnetic 
effect. However, when they are put in a magnetic field, they tend to 
perfectly arrange themselves. So maximum magnetic property is achieved. In 
order to magnetize one of these elements, we use a magnet and we move it 
on the ferromagnetic metal in one direction; so that domains can be 
arranged. Or this is done using the magnetic field created from a 
solenoid, and using it to arrange the domains in one direction.

Returning back to your questions. 
Why is it that only Iron (and it's products, e.g. Steel) is magnetic? 
Could Titanium (for example) become ionized to the point of being 
magnetic?  Does this happen in nature, or via man-made methods which I 
just don't know about?  What are all metals that can become magnets? Why 
or why not?
I guess you can now attribute the answer of every question to a part in my 
discussion. However, I would like to point out that the magnetic property 
is because of the electrons and their pairing, because, as I said, oxygen 
for example may show magnetic properties. So, if  you want to know the 
magnetism of an element or a compound, look at its electron configuration 
and you will know how to categorize it. 

Abbott, A.F. Ordinary Level Physics. Heinemann Educational Books, London. 
Fourth edition 1984.

Blume, Martin. Magnetism. Encyclopaedia Encarta 1997. Microsoft 

Petrucci, Ralph H and Harwood, William. General Chemistry: principles and 
modern applications. Prentice Hall International, INC, USA. Seventh 
edition 1997.

Serway, Raymond. Physics for Scientists and Engineers. Saunders Collage 
publishing, USA. Third updated edition 1990.

Looking forward to your reply,

Moataz Attallah
The American University in Cairo
This is a very good article from Microsoft Encyclopeadia Encarta 97about 
Magnetism Contributed by: Martin Blume 
Magnetism, an aspect of electromagnetism, one of the fundamental forces of 
nature. Magnetic forces are produced by the motion of charged particles 
such as electrons, indicating the close relationship between electricity 
and magnetism. The unifying frame for these two forces is called 
electromagnetic theory . The most familiar evidence of magnetism is the 
attractive or repulsive force observed to act between magnetic materials 
such as iron. More subtle effects of magnetism, however, are found in all 
matter. In recent times these effects have provided important clues to the 
atomic structure of matter.
History of Study 
The phenomenon of magnetism has been known of since ancient times. The 
mineral lodestone (see Magnetite), an oxide of iron that has the property 
of attracting iron objects, was known to the Greeks, Romans, and Chinese. 
When a piece of iron is stroked with lodestone, the iron itself acquires 
the same ability to attract other pieces of iron. The magnets thus 
produced are polarized-that is, each has two sides or ends called 
north-seeking and south-seeking poles. Like poles repel one another, and 
unlike poles attract.
The compass was first used for navigation in the West some time after AD 
1200. In the 13th century, important investigations of magnets were made 
by the French scholar Petrus Peregrinus. His discoveries stood for nearly 
300 years, until the English physicist and physician William Gilbert 
published his book Of Magnets, Magnetic Bodies, and the Great Magnet of 
the Earth in 1600. Gilbert applied scientific methods to the study of 
electricity and magnetism. He pointed out that the earth itself behaves 
like a giant magnet, and through a series of experiments, he investigated 
and disproved several incorrect notions about magnetism that were accepted 
as being true at the time. Subsequently, in 1750, the English geologist 
John Michell invented a balance that he used in the study of magnetic 
forces. He showed that the attraction and repulsion of magnets decrease as 
the squares of the distance from the respective poles increase. The French 
physicist Charles Augustin de Coulomb, who had measured the forces between 
electric charges, later verified Michell's observation with high 
Electromagnetic Theory 

In the late 18th and early 19th centuries, the theories of electricity and 
magnetism were investigated simultaneously. In 1819 an important discovery 
was made by the Danish physicist Hans Christian Oersted, who found that a 
magnetic needle could be deflected by an electric current flowing through 
a wire. This discovery, which showed a connection between electricity and 
magnetism, was followed up by the French scientist André Marie Ampère, who 
studied the forces between wires carrying electric currents, and by the 
French physicist Dominique François Jean Arago, who magnetized a piece of 
iron by placing it near a current-carrying wire. In 1831 the English 
scientist Michael Faraday discovered that moving a magnet near a wire 
induces an electric current in that wire, the inverse effect to that found 
by Oersted: Oersted showed that an electric current creates a magnetic 
field, while Faraday showed that a magnetic field can be used to create an 
electric current. The full unification of the theories of electricity and 
magnetism was achieved by the English physicist James Clerk Maxwell, who 
predicted the existence of electromagnetic waves and identified light as 
an electromagnetic phenomenon.
Subsequent studies of magnetism were increasingly concerned with an 
understanding of the atomic and molecular origins of the magnetic 
properties of matter. In 1905 the French physicist Paul Langevin produced 
a theory regarding the temperature dependence of the magnetic properties 
of paramagnets (discussed below), which was based on the atomic structure 
of matter. This theory is an early example of the description of 
large-scale properties in terms of the properties of electrons and atoms. 
Langevin's theory was subsequently expanded by the French physicist Pierre 
Ernst Weiss, who postulated the existence of an internal, "molecular" 
magnetic field in materials such as iron. This concept, when combined with 
Langevin's theory, served to explain the properties of strongly magnetic 
materials such as lodestone.
After Weiss's theory, magnetic properties were explored in greater and 
greater detail. The theory of atomic structure of Danish physicist Niels 
Bohr, for example, provided an understanding of the periodic table and 
showed why magnetism occurs in transition elements such as iron and the 
rare earth elements, or in compounds containing these elements. The 
American physicists Samuel Abraham Goudsmit and George Eugene Uhlenbeck 
showed in 1925 that the electron itself has spin and behaves like a small 
bar magnet. (At the atomic level, magnetism is measured in terms of 
magnetic moments-a magnetic moment is a vector quantity that depends on 
the strength and orientation of the magnetic field, and the configuration 
of the object that produces the magnetic field.) The German physicist 
Werner Heisenberg gave a detailed explanation for Weiss's molecular field 
in 1927, on the basis of the newly-developed quantum mechanics (see 
Quantum Theory). Other scientists then predicted many more complex atomic 
arrangements of magnetic moments, with diverse magnetic properties.
The Magnetic Field 
Objects such as a bar magnet or a current-carrying wire can influence 
other magnetic materials without physically contacting them, because 
magnetic objects produce a magnetic field. Magnetic fields are usually 
represented by magnetic flux lines. At any point, the direction of the 
magnetic field is the same as the direction of the flux lines, and the 
strength of the magnetic field is proportional to the space between the 
flux lines. For example, in a bar magnet, the flux lines emerge at one end 
of the magnet, then curve around the other end; the flux lines can be 
thought of as being closed loops, with part of the loop inside the magnet, 
and part of the loop outside. At the ends of the magnet, where the flux 
lines are closest together, the magnetic field is strongest; toward the 
side of the magnet, where the flux lines are farther apart, the magnetic 
field is weaker. Depending on their shapes and magnetic strengths, 
different kinds of magnets produce different patterns of flux lines. The 
pattern of flux lines created by magnets or any other object that creates 
a magnetic field can be mapped by using a compass or small iron filings. 
Magnets tend to align themselves along magnetic flux lines. Thus a 
compass, which is a small magnet that is free to rotate, will tend to 
orient itself in the direction of the magnetic flux lines. By noting the 
direction of the compass needle when the compass is placed at many 
locations around the source of the magnetic field, the pattern of flux 
lines can be inferred. Alternatively, when iron filings are placed around 
an object that creates a magnetic field, the filings will line up along 
the flux lines, revealing the flux line pattern.
Magnetic fields influence magnetic materials, and also influence charged 
particles that move through the magnetic field. Generally, when a charged 
particle moves through a magnetic field, it feels a force that is at right 
angles both to the velocity of the charged particle and the magnetic 
field. Since the force is always perpendicular to the velocity of the 
charged particle, a charged particle in a magnetic field moves in a curved 
path. Magnetic fields are used to change the paths of charged particles in 
devices such as particle accelerators and mass spectrometers.
Kinds of Magnetic Materials 

The magnetic properties of materials are classified in a number of 
different ways.
One classification of magnetic materials-into diamagnetic, paramagnetic, 
and ferromagnetic-is based on how the material reacts to a magnetic field. 
Diamagnetic materials, when placed in a magnetic field, have a magnetic 
moment induced in them that opposes the direction of the magnetic field. 
This property is now understood to be a result of electric currents that 
are induced in individual atoms and molecules. These currents, according 
to Ampere's law, produce magnetic moments in opposition to the applied 
field. Many materials are diamagnetic; the strongest ones are metallic 
bismuth and organic molecules, such as benzene, that have a cyclic 
structure, enabling the easy establishment of electric currents.
Paramagnetic behavior results when the applied magnetic field lines up all 
the existing magnetic moments of the individual atoms or molecules that 
make up the material. This results in an overall magnetic moment that adds 
to the magnetic field. Paramagnetic materials usually contain transition 
metals or rare earth elements that possess unpaired electrons. 
Paramagnetism in nonmetallic substances is usually characterized by 
temperature dependence; that is, the size of an induced magnetic moment 
varies inversely to the temperature. This is a result of the increasing 
difficulty of ordering the magnetic moments of the individual atoms along 
the direction of the magnetic field as the temperature is raised.
A ferromagnetic substance is one that, like iron, retains a magnetic 
moment even when the external magnetic field is reduced to zero. This 
effect is a result of a strong interaction between the magnetic moments of 
the individual atoms or electrons in the magnetic substance that causes 
them to line up parallel to one another. In ordinary circumstances these 
ferromagnetic materials are divided into regions called domains; in each 
domain, the atomic moments are aligned parallel to one another. Separate 
domains have total moments that do not necessarily point in the same 
direction. Thus, although an ordinary piece of iron might not have an 
overall magnetic moment, magnetization can be induced in it by placing the 
iron in a magnetic field, thereby aligning the moments of all the 
individual domains. The energy expended in reorienting the domains from 
the magnetized back to the demagnetized state manifests itself in a lag in 
response, known as hysteresis.
Ferromagnetic materials, when heated, eventually lose their magnetic 
properties. This loss becomes complete above the Curie temperature, named 
after the French physicist Pierre Curie, who discovered it in 1895. (The 
Curie temperature of metallic iron is about 770° C/1300° F.)
Other Magnetic Orderings 
In recent years, a greater understanding of the atomic origins of magnetic 
properties has resulted in the discovery of other types of magnetic 
ordering. Substances are known in which the magnetic moments interact in 
such a way that it is energetically favorable for them to line up 
antiparallel; such materials are called antiferromagnets. There is a 
temperature analogous to the Curie temperature called the Neel 
temperature, above which antiferromagnetic order disappears.
Other, more complex atomic arrangements of magnetic moments have also been 
found. Ferrimagnetic substances have at least two different kinds of 
atomic magnetic moments, which are oriented antiparallel to one another. 
Because the moments are of different size, a net magnetic moment remains, 
unlike the situation in an antiferromagnet where all the magnetic moments 
cancel out. Interestingly, lodestone is a ferrimagnet rather than a 
ferromagnet; two types of iron ions, each with a different magnetic 
moment, are in the material. Even more complex arrangements have been 
found in which the magnetic moments are arranged in spirals. Studies of 
these arrangements have provided much information on the interactions 
between magnetic moments in solids.

Numerous applications of magnetism and of magnetic materials have arisen 
in the past 100 years. The electromagnet, for example, is the basis of the 
electric motor and the transformer. In more recent times, the development 
of new magnetic materials has also been important in the computer 
revolution. Computer memories can be fabricated using bubble domains. 
These domains are actually smaller regions of magnetization that are 
either parallel or antiparallel to the overall magnetization of the 
material. Depending on this direction, the bubble indicates either a one 
or a zero, thus serving as the units of the binary number system used in 
computers. Magnetic materials are also important constituents of tapes and 
disks on which data are stored.
In addition to the atomic-sized magnetic units used in computers, large, 
powerful magnets are crucial to a variety of modern technologies. Magnetic 
levitation trains use strong magnets to enable the train to float above 
the track so that there is no friction between the vehicle and the tracks 
to slow the train down. Powerful magnetic fields are used in nuclear 
magnetic resonance imaging, an important diagnostic tool used by doctors. 
Superconducting magnets are used in today's most powerful particle 
accelerators to keep the accelerated particles focused and moving in a 
curved path.

please email me if you need any further help
Moataz Attallah

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