Proton nuclear magnetic resonance study of crystal field levels in praseodymium hydrides

Abstract

We report proton ( 1H) T 1, measurements in the temperature range 8 K ⩽ T ⩽ 300 K for PrH 2.0 and PrH 2.5, as well as for praseodymium-doped YH ≈2. The measured temperature dependence of T 1 in PrH 2.0 and PrH 2.5 is entirely accounted for by the proton spin interaction with fluctuating Pr 3+ electronic moments, and its behavior in PrH 2.0 differs markedly from that in PrH 2.5. The non-zero magnetic moment of the crystalline electric field (CEF) ground state Γ 5 triplet in PrH 2.0 causes the rate R 1 = T 1 −1 to increase with decreasing temperature, yielding very short T 1 values ranging from 100 μs at 300 K to only 30 μs at 8 K. In PrH 2.5 the orthorhombic CEF results in nine singlet levels, with the result that the 1H T 1, is roughly 1000 times longer than in PrH 2.0, and its temperature dependence behaves in the opposite fashion, decreasing with increasing temperature from 250 ms at 8 K to 1 ms at 280 K to 1 ms at 280 K. In praseodymium-doped YH ≈2 the magnitude and temperature dependence of R 1 p show the ground state CEF level to be a non-magnetic singlet.