Nuclear spin-spin relaxation in He-3-He-4 two-phase solid solutions at ultralow temperatures

The spin-spin relaxation time in a He-3-He-4 solid solution is measured bef ore and after phase separation in the temperature range 1-250 mK. The spin echo technique is used, which permits separating the contributions of the t wo separated phases to the magnetic relaxation. It is found that in the con centrated phase the spin-spin relaxation time is practically independent of temperature above 50 mK and is described by the same exchange mechanisms a s in pure He-3. In the dilute phase the relaxation time is inversely propor tional to the concentration and agrees with the corresponding values for ho mogeneous solutions. The dominant contribution to the spin-spin relaxation process is from He-3-He-4 tunneling exchange. At the lowest temperatures th e spin echo exhibits anomalous behavior, which may be a manifestation of qu asi-one-dimensional diffusion. (C) 2000 American Institute of Physics. [S10 63-777X(00)00306-6].