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Magnetic Properties of Metals with Partially Filled 4f Electron Subshells

Posted by Don Mansfield, 20 August 2009 · 2,020 views

Did you ever wonder about the type of debate that goes on before an acquisition rule becomes final and is incorporated into the Federal Acquisition Regulation System? This information can be found in the Background section of the final rule when it appears in the Federal Register. I make a point of reading this section whenever a new rule comes out because it tells the story behind the rule?who the rule is going to affect, who is happy about the rule, who is upset about the rule, who thinks it should be scrapped, what the rule makers were thinking when they created and revised it, etc. This section is also a valuable reference when you are trying to interpret a rule in the FAR System that is unclear or ambiguous.

Typically, the comments received range from pointing out errors in the rule to blatantly self-serving statements from private parties either praising the wisdom of the rule or explaining how the rule will inevitably bankrupt small business concerns, cost the Government more money, and lead to a widespread malaise in the country. The rule makers' responses to the comments range from nonresponsive or evasive to well-written explanations of why the comment is or is not valid (I've generally had good responses to comments that I have submitted for consideration).

DoD recently issued a final rule revising the existing rules on the restriction on the acquisition of specialty metals (DFARS Case 2008-D003). The rule contained a straightforward definition of "high-performance magnet" in the new clause at DFARS 252.225-7009, Restriction on Acquisition of Certain Articles Containing Specialty Metals, as follows:

High performance magnet means a permanent magnet that obtains a majority of its magnetic properties from rare earth metals (such as samarium).

Apparently, the Background statement pertaining to this definition that accompanied the interim rule drew criticism from a number of interested parties. The comments received went so far as to suggest that the definition, as written, would pose a threat to national security:

The respondent disagreed with DoD's Background statement that magnets containing rare earth elements are technologically superior in magnetic performance to other types of magnets, because the technological superiority of one magnet over another is ultimately driven by the requirements of the application where it is used. The respondent also stated that, in addition to maximum energy product, parameters such as temperature stability, temperature range, resistance to demagnetization, corrosion resistance, mechanical toughness, and machinability contribute to the decision as to which type of magnet to use for a military application.
These respondents were also concerned that limiting the definition to rare earth (such as samarium-cobalt) magnets and excluding alnico magnets would increase dependency on Chinese magnets and threaten national security. For example, one respondent expressed concern that, if alnico magnets are not included in the definition, alnico magnets that are COTS items will be exempt from the specialty metals restriction.

DoD's response to these comments brought me back to high school physics class (God bless you, Mr. Michel). Here is an excerpt:

With regard to whether it is meaningful to define ``high performance magnet'' as a permanent magnet that obtains a majority of its magnetic properties from rare earth metals: Cobalt, iron, and nickel are the three primary ferromagnetic metals and, therefore, are present in most, if not all, permanent magnets. However, it is the very strong magneto-crystalline anisotropy (the property of being directionally dependent) of certain rare earth elements that produces the exceptional magnetic behavior in the materials to which they are added. The partially filled 4f electron subshells in rare earths lead to magnetic properties in a manner similar to the partially filled 3d electron subshells in transition elements such as cobalt, iron, and nickel. However, the magnetic moment of a rare earth material is typically an order of magnitude greater than that in a transition element; and rare earths exhibit a large anisotropy due to dipolar interactions. In summary, rare earths possess very unique electron structures that produce extreme anisotropy in their magnetic properties.

I don't know if that is right. However, I did learn a new word (anisotropy) and I now know something about the magnetic properties of rare earth metals and transition elements that I didn't know before.

You may ask: "what good is knowing this?" Other than trying to make someone think that you are smarter than you actually are, there may be no value. However, as evidenced by the discussion in the Background section of the rule, there was a great deal of deliberation about the final definition. A contracting officer may encounter situations where he or she needs to apply the new rule and knowing that the definition of "high-performance magnet" is very narrow will help.

Take a look at the Background section of an acquisition rule the next time one comes out (FAC 2005-036was just issued last week). Not only will it add some life to the rule as it appears in the regulation, you may learn something.


For those who want to research the FACs and FAR Cases from the federal register notices back to the end of 1999, they can click "FAR Research" on the Rules & Tools page.
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