Temperature dependence of Pb³⁺ EPR spectrum in irradiated calcite

Abstract

The spin-Hamiltonian parameters and the line widths of Pb3+ in CaCO, have been measured over the temperature range 77 to 300 "K. The hyperfine interaction is very large so that the intermediate field approximation was used. The hyperfine interaction decreases as the temperature increases, in agreement with the effect of lattice-vibrations on the ground state. The hypothesis of a large-amplitude resonance mode is used for explaining the qualitative temperature dependence. Extra line widths is described to the presence of hyperfine interaction of the 207Pb isotope. A dynamic process is assumed which is related to the change of spin-lattice relaxation via phonon modulation of the hyperfine interaction.Utilisant 1'8pproximation du champ intermkdiaire imposee par la forte interaction hyperfine, on a determine pour les ions Pb3+ en calcite irradi6 les parametres de la hamiltonienne de spin et les largeurs de lignes des spectres R E P dans un intervalle de temperature 77 6, 300 "K. On peut conclure sur la decroissance de I'intdraction hyperfine avec ]'augmentation de la temperature, en accord avec l'effet des vibrations du cristal en &tat fondamental. L'hypothhse d'un mode resonant de grande amplitude est employee pour expliquer qualitativement la dependance de temperature. Les rbsultats exphrimentaux indiquent une largeur supplementaire de lignes du spectre R E P pour le isotope de PbZo7. L'existence d'une modulation de l'interaction hyperfine, determinee par, les vibrations du rksean pourrait expliquer un relaxation supplementaire par un process dynamique.

Theory of the Relaxation Processes for Multilevel Spin Systems in Dilute Paramagnetic Solids at High Temperature

“…(3.30a)). In this case, the Lorentzian EPR linewidth at low temperature ÀR ss mn that represents the magnetic dipole±dipole interactions among spins could be negligible [17,18]. Now, w mn and R mn have comparable values, and the linewidths have a strong temperature dependence, so that the spins relax between them and to the lattice with comparable rates so that T 2 T 1 .…”

Maximization of the efficiency of the frequency conversion with a spin multiplet subjected to three frequency-correlated fields

“…In our treatment, the inhomogeneous broadening mechanisms have been neglected. However, at these high temperatures, for a suitable choice of the dilute paramagnetic sample, the spinlattice relaxation rates are of about 10' s -', and the above approximation could be valid [10,11]. In addition, for changing rates of the field intensities or of the phases up to above 106 s-', Eqs.…”

“…(19)). Thus at relatively low temperatures Tz becomes independent of temperature, while T, <_ TZ has a strong temperature dependence (ocT-', or even an exponential dependence [11]). If the value of the Rabi frequency corresponding to the strong coupling field is much larger than that of the other two fields, the temperature should be low.…”

“…-'(T2 °)-', p^m = 10 -11 G2, and Arp" = -7t/2 (solid line). These results correspond to a four-level spin system of Pb" in calcite[5,11], where B = 10 T, m = 1, o = 2, n = 3, v Q = 262.9 GHz, Q," = 19.7 GHz, and vm = 282.6 GHz (v = rv/2n).…”

“…ConsiderCpam)eCpnQ) « (pmn). (16)In this case^,_ ani T 2na7 27 ((Pmm -p 0 )T, + (P°n -Paa )Tm^n) ( 17 ) T n n z T 2 6 7 , Z a m pmn) + 2T am( T2-(Pna) +TÍm(prnn)) ( )The spin-lattice relaxation time T"am characterizing the three involved levels is:2 2 = T na Tam _ Tno Tvm = Tn° Tmn -Tna Tmn _ TmnTI -Tam T''1 nom on am am na an mit mit no mit Gin mit amAt relatively low temperatures for a spin system: T, raam °C T" TZ -T2, and T, » T2[11]. The coherent mixing (see Eq.…”