  Producing a polarized lanthanum (La) target with high polarization and long
relaxation time is crucial for realizing time-reversal violation experiments
using polarized neutron beams. We use a LaAlO3 crystal doped with a small
amount of Nd3+ ions for the polarized lanthanum target. Optimizing the amount
of Nd3+ ions is considerably important because the achievable polarization and
relaxation time strongly depend on this amount. We established a fundamental
method to grow single crystals of Nd3+:LaAlO3 using an optical floating zone
method that employs halogen lamps and evaluated the crystals with the dynamic
nuclear polarization (DNP) method for polarizing nuclear spins. Two crystal
samples were grown by ourselves and evaluated with the DNP at 1.3 K and 2.3 T
for the first time except for the target materials of protons. The enhancement
of NMR signals for 139La and 27Al was successfully observed, and the
enhancement factors were eventually 3.5+-0.3 and 13+-3 for the samples with
Nd3+ ions of 0.05 and 0.01 mol%, respectively. These enhancement factors
correspond to absolute vector polarizations of 0.27+-0.02% (Nd 0.05 mol%) and
1.4+-0.3% (Nd 0.01 mol%). Although the obtained polarizations are still low,
they are acceptable as a first step. The combination scheme of the crystal
growth and evaluation of the crystals is found to be effectively applicable for
optimizing the amount of Nd3+ ions for improving the performance of the
polarized target.
