[Wien] Unit for the HFF

[Lyudmila Dobysheva]

On Saturday 04 February 2006 13:29, Gerhard Fecher wrote:
> I was wondering about the unit used for the hyperfine field (HFF values).

On Saturday 04 February 2006 16:43, thomas.mazet wrote:
> B = muO.H (+ mu0.M)

On Saturday 04 February 2006 11:02, Gerhard Fecher wrote:
> Maybe A/m is rarely used, it is the correct unit for the field strength in 
> SI unit.  That it was not used a lot in the past millenium does not prevent
> me to teach it correctly to my students.

I have decided to comment this discussion, as nobody did this.
I'll be glad if somebody more learned finds time to correct me.

A translation from Russian:
"Call me a pot if you like, but do not put me in stove"
in Physics:
"Call it a magnetic field, but do not measure it in A/m"

It's the name "hyperfine magnetic field" (HFF) that came from the
past millenium and makes confusion. And units should reflect a
physical meaning, not a name.
In experiments measured is a splitting of the nucleus energy levels. If
it were an empty space there would be only magnetic field H affecting the
splitting. In the substance there is a density of magnetisation in addition.
As Thomas writes: B=muO.H+muO.M

The first term muO.H is not the HFF, it may be an external field used
in Moessbauer experiments sometimes.  The second term muO.M is the
quantity. M is density of magnetisation, in our calculations in the
case.scf file it is spin density (rho_up - rho_down) in the nucleus region.

Sometimes we can even meet words "effective field" concerning the HFF,
this is because it is not a field, it is a magnetic induction. In many
papers you may see "hyperfine magnetic field" in the text, but B as its
designation, and of course, Tesla or kGauss.
Oersted and A/m and designation H are not correct.

Best regards
  Lyudmila Dobysheva 
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