Anisotropic spin diffusion in liquid $^3$He confined in nafen

We report results of spin diffusion measurements in normal phase of liquid $^3$He confined in nafen. Nafen is a new type of aerogel and it consists of Al$_2$O$_3$ strands which are nearly parallel to one another at macroscopic distances. We examine two samples of nafen with different porosities using spin echo techniques. Spin diffusion of $^3$He along and across the strands was measured. The aerogel alignment is clearly evident from observed spin diffusion anisotropy. A theory describing this effect is developed and compared with the experiment.