Observation of higher order NMR larmor lines by SQUID in solids at low magnetic field |
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Authors: | M Kohl M Odehnal V Pet?íěek R Tichý S ?afrata |
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Affiliation: | (1) Institute of Physics, Czechoslovak Academy of Sciences, e, Czechoslovakia |
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Abstract: | We describe an apparatus allowing the observation of the NMR static longitudinal component of nuclear magnetizationM
z
by a SQUID at low magnetic fields and atT=4.2 K in Plexiglas, Teflon, and CaF2. The higher order NMR Larmor lines at 2f
0, 3f
0, and 4f
0, wheref
0 is the Larmor frequency of the allowed NMR line, were measured. These lines correspond to a flip of two, three, and four spins, respectively, by one photon. The amplitudes of 2f
0 and 3f
0 lines and their field dependences show that the common assertion that the forbidden lines at 2f
0 and 3f
0 appear in the same order of perturbation theory and that their intensity decreases with static magnetic fieldB
0 asB
0
–2
is wrong. In fact, the third Larmor line 3f
0 appears at higher order than the second Larmor line 2f
0 and its intensity decreases asB
0
–4
. This is also shown by a theoretical calculation of its intensity. For the first time the NMR SQUID technique allowed the detection of the 4f
0 line, corresponding to the simultaneous flip of four spins by one photon. |
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Keywords: | |
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