Magnetic order of Tb3Co2.2Si1.8 and Dy3Co2.2Si1.8 as a representative of the family of compounds with orthorhombic distortion of rare earth lattice

•Tb3Co2.2Si1.8 and Dy3Co2.2Si1.8 order ferromagnetically below 132 K and 74 K.•They show spin-reorientation transition around 42 K and 35 K.•They are soft ferromagnets in the HT area and permanent magnets in the LT area.•Tb3Co2.2Si1.8 orders with Cmc′m and Cmcm′ magnetic groups in the HT and LT areas.•Tb3Co2.2Si1.8 orders with additional canted flat spiral: K1=[±Kx, 0, 0], Kx≈3/10.

Magnetic measurements indicate that the rare earth intermetallic compounds Tb3Co2.2Si1.8 and Dy3Co2.2Si1.8 (Dy3Co2.2Si1.8-type) exhibit ferromagnetic transition at 132 K and 74 K and a spin-reorientation transition around 42 K and 35 K, respectively. Below Curie temperature, both compounds are soft ferromagnets, whereas below the spin reorientation transition they are permanent magnets with antiferromagnetic component: the values of critical field Hc=30 kOe, coercive field Hcoer=17 kOe and residual magnetization Mres=4.1 μB/Tb for Tb3Co2.2Si1.8 and Hc=14 kOe, Hcoer=21.5 kOe and Mres=3.7 μB/Dy for Dy3Co2.2Si1.8 at 2 K. The magnetocaloric effect of Dy3Co2.2Si1.8 is calculated in terms of isothermal magnetic entropy change (ΔSm) and it reaches a values of −16.5 J/kg K at 75 K for a field change of 140 kOe (−8.1 J/kg K at 70 K, for 0–50 kOe change) and −6.0 J/kg K for a field change of 140 kOe (−1.4 J/kg K, for 0–50 kOe change) around 40 K.Neutron diffraction study in zero applied field shows mixed ferro-antiferromagnetic ordering of Tb3Co2.2Si1.8 below ~127 K with wave vectors K0=[0, 0, 0] and K1=[±Kx, 0, 0] (Kx≈3/10). Between ~127 K and 53 K the magnetic structure of Tb3Co2.2Si1.8 is set of canted ferromagnetic cones with a resulting b-axis ferromagnetic component, whereas below 43 K its magnetic structure is set of canted ferromagnetic cones with a resulting c-axis ferromagnetic component. Between 53 K and 43 K the high-temperature magnetic order of Tb3Co2.2Si1.8 transforms to the low-temperature order via an intermediate state. The level of orthorhombic distortion of the Tb-sublattice determines the magnetic ordering of Tb3Co2.2Si1.8 in the Tb→Tb3Co2.2Si1.8→Tb3Co2Ge3→TbGe sequence.

Graphical abstractTransformation of magnetic ordering of Tb3Co2.2Si1.8Figure optionsDownload full-size imageDownload as PowerPoint slide