Physica B 329–333 (2003) 305–306 Topological defects and coherent magnetization precession of 3 He in aerogel Yuriy Bunkov*, Eddy Collin, Henri Godfrin, Robert Harakaly Centre de Recherches sur les Tr " es Basses Temp ! eratures, CNRS, BP 166, Grenoble 38042, France Abstract Wehaveobservedforthefirsttimetheformationoftheregionwithcoherentprecessionofmagnetization(CPM)in superfluid 3 He in aerogel covered by solid monolayers of 4 He: The signal of CPM has been observed by pulsed NMR and by CW NMR. By playing with the magnetic field gradient we were able to distinguish the spatial position of the region of CPM as well as to determine the long-scale inhomogenity of the order parameter. We have observed an evidence for existence of an enormous number of topological defects in superfluid 3 He in aerogel. r 2003 Elsevier Science B.V. All rights reserved. Keywords: Superfluid 3 He; Aerogel; Topological defects; Ultralow temperature 1. Introduction The properties of superfluid 3 He in aerogel glass has been a subject which has attracted considerable interest over the past few years. The bulk superfluid 3 He is an absolute pure material, which indeed can display many different types of topological defects owing to the complex structure of the order parameter [1]. High densityoftopologicaldefectsinbulk 3 Hecanbecreated by fast cooling [2]. But even at slow cooling the order parameter of 3 He is always inhomogeneous due to the shape of the experimental cell, and it is likely that few topological defects are usually formed in the cell. The defectscanbeannealedbyfastrotation,asitwasshown by Helsinki experiments, or by nonlinear NMR, which can remove some types of magnetic defects [3]. Surpris- ingly, the existence of topological defects in 3 He in aerogel have never been discussed. In Grenoble, we have made systematic studies of properties of superfluid and normal 3 He in aerogel with different coverages of 4 He monolayers. The experiments weredoneusingacylindricalcellwiththeaxisparallelto the magnetic field of order 300 Oe; at temperatures down to 200 mK: The results of our experiments will be published elsewhere. But in this article, we are pointing out the two important observations. In order to explain our results we must suggest the B phase like ordering, which is not sensitive to 4 He coverage, but with high density of topological defects. And also we can report theformationofthedomainwithcoherentprecessionof magnetization by non-linear NMR. 2. Spatial inhomogenity of order parameter There was many theoretical and experimental studies of 3 He in aerogel, where the 3 He was considered as a spatially homogeneous state. The properties of the NMR lines have usually been treated as common liquid plus solid 3 He single lines with broadening due to interactions within the solid and frequency shifts due to the superfluid 3 He: The theoretical consideration was basedonthissimplifiedmodel.Exceptionalmaybeonly the work by the Stanford group, where the signal was treatedasoneradiatedbyaspatiallyorientedtexture [4]. In our work in Grenoble we have found that the single line consideration is correct only for the region of temperatures above the superfluid transition in bulk. Below this temperature, the behavior of NMR signals became much more complicated. First of all, satellite lines appear [5], which we attribute to some regions *Corresponding author. E-mail address: bunkov@polycnrs-gre.fr (Y. Bunkov). 0921-4526/03/$-see front matter r 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4526(02)02062-8