Excitation of Nuclear Magnetic Resonance Modes in Antiferromagnetic KMnF3

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Abstract
The Mn55 nuclear resonance absorption in KMnF3 has been monitored through the observation of antiferromagnetic resonance at 4.2°K and below. It is found that with increasing rf power a second antiferromagnetic resonance grows at a shifted field position. At 4.2°K a shifted resonance can be observed for driving frequencies between 580 and 680 Mc. As the driving frequency is reduced the position of the shifted resonance moves toward that of the unshifted line. These results are interpreted in terms of the nucleation of regions of the sample with nuclear resonance at the driving frequency. Such regions are present in the absence of excitation as the result of electronic pinning. With rf excitation these regions are expected to grow. The power level at which substantial growth takes place is in good agreement with theory.