  R2RhIn8 compounds (space group P4/mmm, R is a rare-earth element) belong to a
large group of structurally related tetragonal materials which involves several
heavy-fermion superconductors based on Ce. We have succeeded to grow single
crystals of compounds with Nd, Dy and Er and following our previous bulk
measurements, we performed neutron-diffraction studies to determine their
magnetic structures. The Laue diffraction experiment showed that the
antiferromagnetic order below the N\'eel temperature is in all three compounds
characterized by the propagation vector k = (1/2, 1/2, 1/2). The amplitude and
direction of the magnetic moments, as well as the invariance symmetry of the
magnetic structure, were determined by subsequent experiments using two- and
four-circle diffractometers. The critical exponents were determined from the
temperature dependence of the intensities below TN.
