We report on the enantiopure single-crystal growth using the Czochralski method and the magnetic properties of the Nd-based monoaxial chiral magnet NdPt2B based on electrical resistivity, specific heat, and magnetization measurements. A peak in the magnetic susceptibility and a λ-type anomaly in the specific heat are observed at TN1=19.5K. Successively, a first-order magnetic transition at Tm=9.5K is observed in the electrical resistivity, specific heat, and magnetic susceptibility. In addition, we observed a new magnetic phase transition, which has previously not been reported, at TN2=11K between TN1 and Tm. We observed multiple plateaus in the low-temperature magnetic phase and constructed a nontrivial magnetic phase diagram, which results from the competitive interactions in this system. Furthermore, we observed an increase and decrease in the in-plane anisotropy in the transverse magnetoresistance, which is related to the change in the magnetic structure.
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