Measurement of nuclear spin relaxation time in lanthanum aluminate for development of polarized lanthanum target

Abstract

A polarized lanthanum target applicable to long-term beam experiments is being developed for the study of spindependent nuclear interactions and the search for the violation of time-reversal symmetry (T-violation) in the spin optics of polarized epithermal neutrons. In addition, a large nuclear polarization away from the thermal equilibrium condition is preferred to flexibly adjust the external magnetic field for maximizing the sensitivity to the T-violation by appropriately controlling the neutron spin rotation, which requires a sufficiently slow relaxation of the nuclear polarization. Therefore, the relaxation time of nuclear polarization (T1) is an essential parameter for our applications. In the present study, a single crystal of lanthanum aluminate doped with neodymium ions is chosen as the target material, assuming the application of the dynamic nuclear polarization technique. We measured the T1 of La and Al by observing the nuclear magnetic resonance in the temperature range of 0.1-1.5 K under a magnetic field of 0.5-2.5 T. The results show that T1 has a distribution of up to 100 h, which can be explained by assuming the electron spin-spin reservoir. We estimate T1 ∼ 1 h at 0.1 K with a magnetic field of 0.1 T, which is one of possible conditions for the T-violation experiment. Possible improvements to achieve a longer T1 that is desirable for the T-violation experiment are discussed.