* Corresponding author. E-mail address: dtayursk@mi.ru (D.A. Tayurskii) Physica B 284}288 (2000) 1686}1687 Investigations of dielectric Van Vleck paramagnets at high magnetic "elds and low temperatures Dmitrii A. Tayurskii*, Murat S. Tagirov, Haruhiko Suzuki Physics Department, Kazan State University, Kremlevskaya str., 18, Kazan 420008, Russia Faculty of Science, Kanazawa University, Kakuma-machi, Kanazawa 920-11, Japan Abstract The in#uence of high magnetic "elds on the magnetic properties of dielectric Van Vleck paramagnets is discussed. The dynamics of coupled electron}nuclear spin system is investigated at high magnetic "elds and low temperatures.  2000 Elsevier Science B.V. All rights reserved. Keywords: High magnetic "eld; Nuclear magnetic resonance; Van Vleck paramagnet 1. Introduction Among di!erent dielectric crystals of rare-earth (RE) compounds the so-called `Van Vleck paramagnetsa form a special class. These substances have no magnetic mo- ment in their ground electronic state, but their paramag- netic susceptibility strongly exceeds the diamagnetic one. Van Vleck paramagnetism takes place in crystals con- taining non-Kramers RE ions, for example, Tm. The isotope Tm (100% natural abundance) has a nuclear spin equal to   so the compounds of this element possess both electronic and nuclear magnetism. The so-called `enhanceda nuclear magnetic resonance is the main method of investigation for the Van Vleck paramagnets (see, for example, Refs. [1,2]). Almost all investigations have been carried out at magnetic "elds where the Zee- man energy of an ion can be considered as a perturba- tion. In Ref. [3], we proposed that dielectric Van Vleck paramagnets at high magnetic "elds (above 5 T) could be used for the nuclear dynamic polarization. In Ref. [4], the high-frequency electron paramagnetic resonance and res- onant far-infrared absorption were observed for the "rst time at high magnetic "elds in thulium ethylsul- phate Tm(C  H  SO  )  ) 9H  O(TmES) crystals. These investigations showed that new, essential information about Van Vleck paramagnets can be obtained at high magnetic "elds. It is natural to expect that at high magnetic "elds the dynamics of the nuclear spin system will also exhibit new features. Foremost it is connected with the drastic change of ion wave functions due to the applied high magnetic "eld. In the present work we consider the electron}nu- clear spin system of Tm ion in TmES. 2. Electron}nuclear states at high magnetic 5elds Owing to its ground multiplet of H  manifold, the system under consideration can be described by the e!ec- tive Hamiltonian H"H  #H  #H  #H  , (1) where H  represents the in#uence of electric crystal "eld (the explicit form for it can be found in Ref. [1]), H  and H  stand for the electron and nuclear Zeeman interac- tions, respectively, H  describes the hyper"ne interac- tion. The e!ects of electron}phonon interaction are not taken into account here for simplicity. The numerical procedure of diagonalization of the Hamiltonian (1) allows us to "nd all magnetic quantities for Tm ions in TmES crystal in the dependence on the strength of the applied magnetic "eld and the orientation of this "eld with respect to crystallographic axes (angle ). 0921-4526/00/$ - see front matter  2000 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 2 9 0 2 - 6