Transient nutations decay: The effect of field-modified dipolar interaction

Abstract

The anomalous behavior of transient nutations is experimentally investigated in a set of two-level (Sϭ 1 2 ) spin systems differing only in spin concentration. Our results show that the non-Bloch power dependence of the decay rate of transient nutations is a concentration-dependent effect, which is more and more pronounced in more and more concentrated samples. The experimental results are interpreted in the framework of the recent theory by Shakhmuratov et al. ͓Phys. Rev. Lett. 79, 2963 ͑1997͔͒ and support the hypothesis that the anomalous decay of transient nutations in solids originates from radiation-induced changes of the dipolar field, rather than from residual fluctuations of the nominally coherent field. ͓S1050-2947͑99͒03905-0͔ PACS number͑s͒: 42.50. Md, 76.30.Mi, 76.90.ϩd

Coherence times and Rabi oscillations in CaWO4:Cr5+ crystal

“…4A (S band). As in recent papers [4][5][6][7][8][9][10][11][13][14][15], the observed RO decay rates exceeded both T À1 1 and T À1 M values and depended linearly on Rabi frequency. In order to give theoretical interpretation of this anomalous decay, we perform direct calculation of RO in the presence of strong inhomogeneous broadening of ESR line and MW magnetic field distribution inside the resonator.…”

“…Finally, we would like to draw comparison between our model of decay of Rabi oscillations and the stochastic semi-phenomenological model of Shakhmuratov et al [14,15]. In their model, they suggest that in the presence of resonant external MW magnetic field B 1 e Àix 0 t in the crystal also appears additional stochastic component transverse to B 0 and with the amplitude proportional to B 1 , namely, B 1 ðh 1 ðtÞ þ ih 2 ðtÞÞe Àix 0 t [14].…”

“…Up to now, there is a considerable number of publications indicating anomalously fast damping of Rabi oscillations (RO) of paramagnetic impurities diluted in crystal matrices. Probably the first observations were carried out for E 0 -centers in glassy silica and for [ AlO 4 ] 0 centers in quartz [13][14][15]. They revealed the peculiar linear dependence of s À1 R on X R :…”

“…Apart from [13][14][15], the anomalous damping of RO was observed recently in Er 3+ -doped [4,5] and Yb 3+ -doped [6] CaWO 4 crystals, in molecular magnets Fe 4 [8] and V 15 [9,10], in MgO:Mn 2+ [7] and in K 3 NbO 8 :Cr 5+ [11]. For ordinary experimental conditions, the second term in (1) prevails over the first one.…”

“…The term T À1 M =2 is explained in the framework of Bloch model [13]. However, to the best of our knowledge, there is still no satisfactory explanation of the term linear in X R , except, perhaps, the stochastic semi-phenomenological model developed in [14,15]. Another distinctive feature of RO is its decay pattern which is usually weaker than exponential, containing tens of residual oscillations [4,6].…”