In R-Ni-In system for R=Tb-Tm, the compounds with the stoichiometry near to 2:2:1 crystallize in two different crystal structures:

1. tetragonal one of the Mo₂BFe₂-type (space group P4/mbm for nonstoichiometric   composition R₂Ni_1.78In and
2. an orthorhombic one of the Mn₂AlBe₂-type (space group Cmmm) for stoichiometric R₂Ni₂In.

The both structures consists of the different types of atomic planes perpendicular to the c-axis. One containing only the rare earth atoms and other composed by the Ni and In atoms. The rare earth atoms are located at C₂ point symmetry positions, which have different orientation in the two structures. The C₂ axes in the tetragonal structure are perpendicular to each other, while in orthorhombic one are parallel to each other.

Magnetic and neutron diffraction data indicate that these compounds are antiferromagnet with the different magnetic structures. The  dependence of the Néel temperature on the de Gennes function is fulfilled for nonstoichiometric and not fulfilled for stoichiometric one. The magnetic moments are localized only on the R elements. For nonstoichiometric compounds the magnetic orders are described by the propagation vector k=[k_x,k_x,1/2] for k_x equal ¼ for Tb, Er and Tm and 0.3074 for R=Ho [1]. For stoichiometric magnetic order is described by k=[1/2,1//2,1/2] for R=Tb [2], k=[1/2,0,1/2] for R=[Er and Tm [3] and k=[0.24,1,0.52] for R=Ho [2].  Direction of the magnetic moments are parallel to the c-axis for R=Tb and Ho in both systems and lie in ab plane in nonstoichiometric one and is parallel to the b-axis for stoichiometric one for R=Er and Tm. The change of the direction of the magnetic moments are connected with the change of the sign of the Stevens operator α_J from negative For R=Tb and Ho to positive for Er and Tm. Those confirm influence of the crystal electric field (CEF) in stabilizing of the magnetic structure. In both systems the antiferromagnetic coupling along the short c-axis is observed.

The difference in the magnetic structures observed in (001) plane results from the difference in the distribution in plane the two structural elements: square TbIn ( CsCl- type) and triangle TbNi₂ (AlB₂- type).

For R₂Ni_1.78In the distribution of these elements form the chain along the [110] direction, while for R₂Ni₂In form chain along a-axis and alternating chain from triangles and squares  along b- axis. Competition of two interactions: RKKY and crystal electric field (CEF) lead to complicated magnetic structures [4].