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

Abstract

Magnetic measurements indicate that the rare earth intermetallic compounds Tb3Co2.2Si1.8 and Dy3Co2.2Si1.8 (Dy3Co2.2Si1.8-type) exhibit ferromagnetic transition at 132K and 74K and a spin-reorientation transition around 42K and 35K, 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=30kOe, coercive field Hcoer=17kOe and residual magnetization Mres=4.1μB/Tb for Tb3Co2.2Si1.8 and Hc=14kOe, Hcoer=21.5kOe and Mres=3.7μB/Dy for Dy3Co2.2Si1.8 at 2K. The magnetocaloric effect of Dy3Co2.2Si1.8 is calculated in terms of isothermal magnetic entropy change (ΔSm) and it reaches a values of −16.5J/kgK at 75K for a field change of 140kOe (−8.1J/kgK at 70K, for 0–50kOe change) and −6.0J/kgK for a field change of 140kOe (−1.4J/kgK, for 0–50kOe change) around 40K.Neutron diffraction study in zero applied field shows mixed ferro-antiferromagnetic ordering of Tb3Co2.2Si1.8 below ~127K with wave vectors K0=[0, 0, 0] and K1=[±Kx, 0, 0] (Kx≈3/10). Between ~127K and 53K the magnetic structure of Tb3Co2.2Si1.8 is set of canted ferromagnetic cones with a resulting b-axis ferromagnetic component, whereas below 43K its magnetic structure is set of canted ferromagnetic cones with a resulting c-axis ferromagnetic component. Between 53K and 43K 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.