Appl. Magn. Reson. 14, 525-544 (1998) Applied Magnetic Resonance © Springer-Verlag 1998 Printed in Austria Magnetic Resonant and Non - Resonant Investigations of LiLnF 4 (Ln = Y, Tm) Powders A.V. Klochkov', S. P. Kurzin', I. R. Mukhamedshin' ^ z , D. R. Nabiullin', V. V. Naletov', H. Suzuki', I. Kh. Salikhov', M. S. Tagirov " 2 , D. A. Tayurskii''z, and R. Sh. Zhdanov' 'Kazan State University, Kazan, Russian Federation ' Department of Physics, Faculty of Science, Kanazawa University, Kanazawa, Japan Received September 12, 1997 Abstract. The properties of dielectric powders of the Van Vleck paramagnet LiTmF 4 and its dia- magnetic analogue LiYF 4 have been investigated by both resonant methods (EPR, NMR, and the mass-spectroscopy) and non-resonant ones (conductometry and magnetization measurement). On the basis of experimental data and theoretical calculations a self-consistent model for the magnetic and other properties of these powders is suggested. Two structural phase transitions induced by the mag- netic field are discovered in fine LiTmF4 powder at low temperature in a high magnetic field. 1. Introduction A new approach related to investigations of both magnetism and structure of a substrate surface seems to be found for solving the long-life problem on the nature of a magnetic coupling between the liquid helium-3 and a solid substrate [1-4]. The present work is done within the development of that approach. In order to obtain more information the resonant methods of investigation (EPR, NMR, and the mass-spectroscopy) as well as the non-resonant ones (conduc- tometry, magnetization measurements) are used. Although a surface of fine par- ticles is a rather complicated object for investigation, theoretical calculations and estimations are carried out everywhere if possible. Various experimental results combined with a theoretical study enable us to give a self-consistent picture of the magnetic and other physical properties of rare-earth tetrafluoride (LiLnF 4 ) fine powders. These investigations seem to be of interest not only for a deeper understanding of the nature of magnetic coupling, but also for the verification of a possibility to realize the proposed idea on a dynamic nuclear polarisation of the liquid 3 He with the use of the Van Vleck paramagnets (see [3]). A certain step toward this direc-