Physica B 329–333 (2003) 324–326 Homogeneous spin precession in superfluid 3 He confined to aerogel Vladimir V. Dmitriev a , Ivan V. Kosarev a, *, Norbert Mulders b , Vladislav V. Zavjalov a , Dmitry Ye. Zmeev a a Kapitza Institute, Kosygina Street, 2, Moscow 117334, Russia b Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 USA Abstract We report on systematic studies of creation and relaxation of a macroscopic region of homogeneous spin precession (homogeneously precessing domain—HPD) in B-like phase of 3 He in aerogel. Long lived free induction decay signal has been observed after filling up the whole cell with the HPD and switching off the CW radiofrequency field. Characteristics of CW NMR and free induction decay signal were found to be similar to those known for bulk 3 He-B. r 2003 Elsevier Science B.V. All rights reserved. Keywords: Superfluidity; 3 He; Aerogel By present time a number of NMR experiments [1,2] performed in superfluid 3 He confined within 4 He preplated aerogel have made it clear that a low temperature phase has a B-type structure of the order parameter. In the bulk superfluid 3 He-B the order parameter gradients result in the existence of spin supercurrents which can play a vital role in spin dynamics. In particular they result in existence of homogeneously precessing domain (HPD) [3,4].Amain feature of the HPD is a coherent (i.e. with nearly the same phase) precession of the magnetization in a cell in presence of a magnetic field gradient. The HPD can be created, e.g. in CW NMR experiments [5]. If we switch off a radiofrequency (RF) excitation after the HPD formation then the volume of the HPD would decrease and a domain wall (which separates the HPD and the remaining part of the sample with equilibrium value of the magnetization) would move from a region of higher magnetic field to a lower one. The precession frequency of the HPD equals the Larmor frequency in the middle of a domain wall. Therefore the frequency during the relaxation follows the wall position and in case of constant dissipation (as it usually takes place) changes linearly with the time. In recent CW NMR experiments in Grenoble [6] the HPD-like signal was observed in B- phase of 3 He in aerogel. However, the obtained signal was rather short, i.e. only small part of the cell was probably occupied by the HPD. In our experiments we have succeeded in filling up the entire volume of the cell with the HPD. Experimentswereperformedatapressureof25:5bar; in magnetic field of 284 Oe (NMR frequency was 923 kHz). An experimental cell design is described in Ref. [7]. An important feature of the design is a finite gap ð0:15mmÞ between the aerogel sample and the cell walls. An external magnetic field consisted of homo- geneous component as well as linear gradient compo- nent created by a separate coils. In order to create the HPD the homogeneous component of the external magnetic field was slowly swept down (the initial value ofthefieldexceededthevalue o RF =g)inpresenceofRF- field.ItwasfoundthatathighenoughamplitudeofRF- field (about 0:01 Oe) the NMR line drastically changed anditsformcorrespondedtotheHPDformationjustas it is known for the bulk 3 He-B [5]. A solid curve on Fig.1 shows a formation and further growth of the HPD while lowering an external magnetic field. Finally the HPD occupied almost the entire volume of the experimental cell. If the field is swept up after the *Corresponding author. E-mail address: ivan@kapitza.ras.ru (I.V. Kosarev). 0921-4526/03/$-see front matter r 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0921-4526(02)02071-9