Depending on how large a sample you're inserting into the coil, your
magnetic particles may significantly change both the inductance and the
Q of the coil. You will need to allow for tuning of either the
generator frequency or the matching network to allow for the resonant
frequency shift, and if the Q changes enough, you may need to worry
about adjusting the matching network to get maximum power transfer as
well.
As Win noted, it's the number of ampere-turns that counts. Extending
that thought a bit, a particular amount of energy stored in the tank
circuit consisting of the coil and its resonating capacitor will yield
a particular magnetic field strength, for a given overall coil geometry
(diameter, length, ...). It does not matter what the
coil inductance
is--it does not matter how many turns it has. When the voltage across
the resonating capacitor is zero, all the stored energy is in the
inductor: in other words, in the magnetic field. And the stored
energy at a particular frequency is proportional to the exciting power
level and the Q of the tank circuit.
Continuing the power level though, assume you have a 5 watt source and
you can get that 5 watts coupled into your tank circuit. Then if there
is no sample inside the coil, and the capacitors have very low loss,
practically all 5 watts will be dissipated in the wire of the coil.
But if you put your magnetic sample in the coil and you expect it to
heat up, if you would like to be dissipating 2 watts in your sample,
then the coil will be dissipating only 3 watts. The power dissipated
must add up to the power fed to the tank circuit. And that means that
the Q will be lowered to 3/5 of what it originally was. So if you have
an idea how much actual power your sample will be dissipating when you
are getting the results you desire, you can estimate how much the Q
will be lowered. How much power DO you expect the sample to dissipate?
As you move to higher frequencies, you'll find it easier to make the
coil Q higher. The Q will go very nearly as the square root of
frequency, so in your 1cm diameter coil (assuming about 1cm long), and
assuming just solid copper wire, you'll go from a Q of maybe 35 at
1MHz (with no sample) to a Q of a little over 100 at 10MHz. That will
make it easier to get to high field strengths, but harder to keep it
tuned: a couple percent change in coil inductance as you introduce
your sample will cause a signidicant change in tuning.
How big a sample do you have, relative to the coil size? How uniform
do you need to keep the field? It may actually be easiest to go to a
larger diameter coil and find a bit more power to excite it with, if
you need to, though the larger diameter will also yield a higher Q,
which will mitigate to some extent the need for more power.
Cheers,
Tom