Effect of surface magnetism of solid-state substrates on the NMR of liquid 3 He A. V. Klochkov, V. V. Naletov, M. S. Tagirov, and D. A. Tayurski  Kazan State University, 420008 Kazan, Russia Submitted 21 January 1999; resubmitted 24 February 1999 Pis’ma Zh. E ´ ksp. Teor. Fiz. 69, No. 7, 503–509 10 April 1999 The results of investigations of the longitudinal relaxation rate of the nuclear spins of liquid helium-3 in contact with finely dispersed LiYF 4 dielectric powders with various degrees of filling of the microcracks on the crystal surface by water molecules are reported. It is found that exchange correlations appear between paramagnetic defect centers on the surface as a result of spin-density transfer via the molecular orbitals of oxygen in the water molecule. © 1999 American Institute of Phys- ics. S0021-36409900807-5 PACS numbers: 67.55.-s, 76.60.Es, 75.30.Pd The success of the method of NMR of the nuclei in liquid 3 He for investigating the unusual properties of this quantum liquid at low and ultralow temperatures is well known. One such effect is the presence of magnetic coupling of the nuclear spins of liquid helium-3 and the magnetic moments of a solid-state substrate. The nature of this coupling is still not completely understood, even though the effect of the container walls on the magnetic relaxation of spins in liquid helium-3 was observed 40 years ago. 1 In Refs. 2 and 3 it was established reliably that magnetic coupling exists between the nuclear spins of 19 F fluorine present in the microspheres of finely dispersed 0.2  m DLX-6000 polytetrafluoroethylene powder, and in Ref. 4 transfer of magnetization from the 19 F nuclear spins to protons present in polystyrene microspheres via the nuclear spins of liquid helium-3 was observed. The cross relaxation observed in Ref. 5 between the nuclear magnetic moments of 169 Tm in thulium ethylsulfate and the nuclear spins of liquid 3 He stimulated the investi- gation of magnetic coupling between liquid helium-3 and dielectric Van Vleck paramag- nets. The magnetic relaxation of liquid 3 He in contact with single crystals of the dielectric Van Vleck paramagnet LiTmF 4 and its diamagnetic analog LiYF 4 was investigated in Ref. 6. It was found that the magnetic relaxation of the nuclear spins of liquid 3 He present in the gap between two LiYF 4 single-crystal surfaces acquires substantially new features as compared with relaxation in a bulk liquid. Thus, according to the Bloembergen–Purcell–Pound BPP theory, 7 at temperatures 1–4 K the longitudinal and transverse relaxation in bulk liquid 3 He are governed by the modulation of the dipole– dipole interaction by the diffusive motion and have the same rates, of the order of 10 -3 s -1 . Even though the gap width is macroscopic (10 -4 m, the experimental results attest to the existence of a large increase in the relaxation rates, and the transverse relaxation JETP LETTERS VOLUME 69, NUMBER 7 10 APRIL 1999 539 0021-3640/99/69(7)/7/$15.00 © 1999 American Institute of Physics