Nuclear pseudomagnetism in holmium ethylsulphate: New mechanisms of nuclear relaxation

Abstract The dependence of the neutron precession on the nuclear polarization inside a single crystal of holmium ethylsulphate has been used to measure the pseudomagnetic moment μ ∗ of 165 Ho as well as the spin-lattice relaxation time T 1 for both 165 Ho and 1 H for the applied field H 0 parallel to the crystal c -axis. T 1 ( 1 H) is very long and probably arises from paramagnetic impurities. T 1 (Ho) = 15 min independent of temperature for 2 T K −1 in qualitative agreement with a numerical estimate for a direct process between the two lowest hyperfine levels. T 1 ( 1 H) has also been measured for H 0 ⊥ c . In this orientation T 1 ( 1 H ) = 50 exp (0.09/T) s between 10 −1 . This extremely fast relaxation is qualitatively explained by a thermal coupling between the proton Zeeman system and the spin-spin system of the holmium nuclei. An order of magnitude calculation for such a mechanism is in agreement with the experimental results. For the pseudomagnetic moment of 165 Ho we find μ ∗ /μ B = −0.74±0.08 , somewhat different from a previous value obtained by a neutron diffraction experiment μ ∗ /μ B = −0.59±0.05 .