Non-magnetic Metals

name         Shannan
status       student
grade        9-12
location     CO

Question -   What metals are not magnetic?
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There is not a simple answer. For a metal (or any other substance) 
to be magnetic, it must have electron spin. This gives the substance 
an electronic angular momentum to interact with the magnetic field. 
Some metals, like the lanthanides, consistently have unpaired 
electrons due to the Pauli Exclusion Principle, and so are typically 
strongly magnetic. But other metals may be magnetic or not magnetic 
depending upon what substance they are found. Alloys made of 
nominally magnetic metals such as Fe and Ni may become non-magnetic 
in certain alloys grouped together as "stainless steel". In 
addition, the term "magnetic" is not very precise. Some substances 
become "magnetic" in the presence of a magnetic field, but are not 
magnetic in the absence of a magnetic field. These are called 
"paramagnetic". Other substances form "permanent" magnets and have 
their own intrinsic magnetic field. These are called "ferromagnetic" 
materials because iron metal is the "typical" example. Yet other 
substances have a structure in which some of the electrons point in 
one direction and another layer of domain point in the opposite 
direction. These more complex structures are called 
"antiferromagnetic". A further complication is that the magnetic 
behavior depends upon the temperature. So at low temperature a 
substance may have one kind of magnetic properties but at a higher 
temperature may have another type of magnetic behavior.
    The bottom line is that the magnetic properties of a substance 
 is complicated, and it is hard to assign metals as being strictly 
 magnetic and others to be strictly non-magnetic.

You might find the attached article from the 16 May edition of the 
New York Times (on-line) interesting:

http://www.nytimes.com/2006/05/16/science/16qna.html

Vince Calder
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Dear Shannan,

Numerous metals are not ferromagnetic.  Common examples are copper, 
silver, aluminum, lead, magnesium, platinum and tungsten.  All 
materials, however, react to magnetic fields in one of three ways:

Ferromagnetic materials, such as iron, cobalt, and nickel, have 
small domains in which all the atoms line up with their permanent 
magnetic moments pointing in the same direction.  When an external 
magnetic field is applied, the domains pointing in the direction of 
the field grow at the expense of other domains producing a very 
strong magnetic field in the direction of the external field.  When 
the external field is removed, the domains remain aligned, producing 
a permanent magnet.

In paramagnetic materials,  such as aluminum, magnesium, and 
platinum, the atoms have permanent magnetic moments, but do not form 
domains.  An external magnetic field tends to line the atoms up 
parallel to the external field, but the effect is much smaller and 
is proportional to the external field, so when the external field is 
removed, the atoms point randomly and no permanent effect remains.

In diamagnetic materials, such as copper, lead, and silver, the 
atoms have no permanent magnetic moment.  The effect of an external 
magnetic field is small (similar to paramagnetic materials) and in 
the opposite direction.

As you can see, the subject is complicated, but these are the main ideas.

Best, Dick Plano, Professor of Physics emeritus, Rutgers University
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Virtually anything that we commonly think of as matter can be 
influenced by a magnetic field,
provided certain conditions are met.  However, for the most part 
there are only 3 elements (and then
compounds made that include those elements) which are commonly 
thought of as magnetic: Iron, Nickel, and
Cobalt.   While most any matter can be influenced by a magnetic 
field, these 3 elements are thousands of times more
susceptible to the effects of a magnetic field.  Their interaction 
is so strong, their effects so dramatic, and other
things so weak or subtle, that we generally just think of other 
things as not "magnetic".

The reason these three metals are so strongly magnetic is not 
completely understood.  Their
outer-most electrons tend to possess spins that line-up.   This 
alignment, whatever the reason, is what
gives cobalt, iron and nickel their very strong magnetic properties 
compared to most other materials.

Michael Pierce
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