Field induced multiple magnetization plateaus in NdPt2B studied by single crystal neutron diffraction.

NdPt2B crystallizes in a non-centrosymmetric hexagonal structure. Resistivity, specific heat and susceptibility data reveal three antiferromagnetic transitions at TN1 = 19.5 K, TN2 = 11 K, and a first-order transition at Tm = 9.5 K. Our neutron diffraction study on powder and single crystal samples (with B-11) using D20 and WISH instruments revealed an original ground state. It can be represented as a superposition of three unharmonic spin density waves, combining k=(0,0,1/5), 2k=(0,0,2/5) and k=0 components at 2K, with moments polarized within the (ab)-plane and forming 60- and 120-degrees configuration. The stacking of the moments along the c-axis follows +-++-+ sequence, where + and – stand for positive and negative moment direction along the in-plane easy axes of the spin density waves. Interesting the magnetization isotherm for H//a-axis at 2 K and below 2 T exhibits multiple magnetization plateau (five metamagnetic transitions) and saturates above it. The prosed magnetic ground state can naturally explain this behaviour by assuming that magnetic field flips some negative spins to positive, changing the periodicity (propagation vector) of the structure. We, therefore, proposed to carry out a single crystal neutron diffraction study in applied field (H//-axis) on NdPt2B to investigate the changes in the magnetic structure across the magnetization plateau.