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