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Name: Shannan
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Question:
What metals are not magnetic?



Replies:
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


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


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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