Neutron diffraction study of magnetically ordered ${\mathrm{Tm}}_2$${\mathrm{Fe}}_3$${\mathrm{Si}}_5$

${\mathrm{Tm}}_2$ ${\mathrm{Fe}}_3$ ${\mathrm{Si}}_5$ has been studied at low temperatures by neutron powder diffraction techniques. At T=1.5 K the diffraction pattern is characteristic of a tetragonal crystal structure, space group P4/mnc ($D_{4h}^6$; with a=10.332 Å and c=5.388 Å), similar to that of the prototype compound ${\mathrm{Sc}}_2$ ${\mathrm{Fe}}_3$ ${\mathrm{Si}}_5$. Below T=1.2 K magnetic scattering peaks develop, which can be indexed with the parameters of the chemical cell. A noncollinear antiferromagnetic structure is proposed which features ordering of Tm moments in the 〈110〉 set of directions. The magnetic moment of Tm is 6.5${\mu }_B$ at the lowest temperature attained, 0.35 K.