Separation of crystal-field levels and phonons in Pr dideuteride using polarized neutrons

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Abstract
Polarized neutrons with polarization analysis are used for the first time successfully for distinguishing crystal-electric-field (CEF) excitations from phonons by investigating both the spin-flip and non-spin-flip cross sections. From this, it is shown that the 20 meV peak in Pr dideuteride, observed previously with unpolarized neutrons, arises from CEF excitations. Since this energy is nearly half the value of the CEF level at 41 meV known before, the 20 meV peak is composed of two contributions. At low temperatures it only arises from transitions from the ground state into the 20 meV level. At room temperature, on the other hand, the 20 meV level is thermally populated, so that transitions from the 20 meV into the 41 meV level are also obtained. This leads to the unexpected increase of the intensity of the 20 meV peak at increasing temperatures observed previously. The present result gives a strong contribution to the knowledge of the CEF parameters of the Pr3+ ions in PrD2.