Neutron powder diffraction study of the nuclear and magnetic structures of HoNi 1.985Co 0.015B 2C and HoNiBC

Abstract

The nuclear and magnetic structures of HoNi 1.985Co 0.015B 2C and HoNiBC have been analyzed by neutron powder methods. The first of these materials crystallizes with the symmetry of space group I4/mmm, lattice parameters (at room temperature) a = 3.52011(9), c = 10.5286(3) A ̊ , and is isostructrural with the undoped compound HoNi 2B 2C. Cobalt and nickel atoms are disordered over the same crystallographic sites. Well below the Neèl temperature (∼ 8 K), the magnetic moments of the Ho atoms are ordered ferromagnetically in the a, b planes and antiferromagnetically along the c-axis, with a magnitude of the moment of 8.26(6) μ B. The Co doping, even at such low concentrations, destroys the superconducting behavior of the undoped phase. The compound HoNiBC is also tetragonal (space group P4/nmm), with lattice parameters (at room temperature) a = 3.5631(2), c = 7.5486(6) A ̊ , and is isostructural with LuNiBC. Below the Neèl temperature (9.82(8) K), the Ho magnetic moments are ordered ferromagnetically in the bi-layers (HoC)(HoC) with spins lying in the a, b planes, and successive bi-layers are ordered antiferromagnetically along the c-axis. The magnitude of the moments is 6.74(9) μ B. No structural distortions associated with the magnetic ordering were observed in either compound.