Magnetic order of Tb3Co2.2Si1.8 and Dy3Co2.2Si1.8 as a representative of the family of compounds with orthorhombic distortion of rare earth latticeстатья
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Аннотация:Magnetic measurements indicate similar magnetic ordering of Dy3Co2.2Si1.8-type Tb3Co2.2Si1.8 and Dy3Co2.2Si1.8. The Tb3Co2.2Si1.8 and Dy3Co2.2Si1.8 exhibit ferromagnetic-type transition at 132 K and 74 K and they show spin-reorientation transition around 42 K and 35 K, respectively. Below Curie point both compounds are soft ferromagnets, whereas below low-temperature transition they are permanent magnets with antiferromagnetic component (critical field Hc = 30 kOe, coercive field Hcoer = 17 kOe and residual magnetization Mres = 4.1 mB/Tb for Tb3Co2.2Si1.8 and Hc = 14 kOe, Hcoer = 21.5 kOe and Mres = 3.7 mB/Dy for Dy3Co2.2Si1.8 at 2 K). The magnetocaloric effect of Dy3Co2.2Si1.8 is calculated in terms of isothermal magnetic entropy change (dSm) 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, 0-50 kOe) and –6.0 J/kg*K for a field change of 140 kOe (–1.4 J/kg*K, 0-50 kOe) 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 resulting b-axis ferromagnetic component, whereas below 43 K its magnetic structure is set of canted ferromagnetic cones with 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, like in Dy3Co2.2Si1.8.