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.

Transformation of magnetic ordering of Tb3Co2.2Si1.8Figure optionsDownload as PowerPoint slide