Evidence of tetragonal to orthorhombic distortion of HoNi2B2C in the magnetically ordered state

Using high resolution neutron scattering on a powder sample of HoNi2 (B2C)- B-11 magnetoelastic effects are observed in this compound for the first tim e. At low temperatures the tetragonal lattice is distorted along the [110] direction, in which the long-range ordered Ho moments are aligned. The leng th of the unit cell in [110] direction is shortened by about 0.19% compared to its length in [(1) over bar 10] direction. This lattice distortion is c onsidered to be related to the existence of the commensurate c-axis modulat ed antiferromagnetic structure. (C) 1999 American Institute of Physics. [S0 021-8979(99)16208-X].