Magnetic ordering of Hf3Ni2Si3-type {Sm, Tb, Er}3Co2Ge3 and {Tb, Ho}3Ni2Ge3 compoundsстатья
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Аннотация:The magnetic ordering of Hf3Ni2Si3-type {Sm, Tb, Er}3Co2Ge3 and {Tb, Ho}3Ni2Ge3 compounds (space group Cmcm, oC32) was investigated via magnetizatiom measurements and neutron diffraction study in a zero-applied field. {Sm, Tb, Er}3Co2Ge3 and Ho3Ni2Ge3 exhibit field sensitive complex antiferromagnetic orderings with TN = 51 K, Tm = 10 K for Sm3Co2Ge3, TN = 34 K, Tm = 13 K for Tb3Co2Ge3, TN = 7 K for Er3Co2Ge3 and TN = 11 K for Ho3Ni2Ge3. At 2 K and above the critical field of ~5 kOe, 20 kOe, 4 kOe and 7 kOe for Sm3Co2Ge3, Tb3Co2Ge3, Er3Co2Ge3 and Ho3Ni2Ge3, respectively, saturation magnetizations per rare-earth atom are 6.5 mB for Tb3Co2Ge3, 7.0 mB for Er3Co2Ge3 and 8.0 mB for Ho3Ni2Ge3 in the field of 140 kOe, whereas magnetization of Sm3Co2Ge3 has an antiferromagnetic behaviour. The isothermal magnetic entropy change, dSm, indicates a field-induced ferromagnetic ordering in Sm3Co2Ge3, Tb3Co2Ge3, Er3Co2Ge3 and Ho3Ni2Ge3 with a maximal dSm value of -10.9 J/kgK for Ho3Ni2Ge3 at 11 K for a field change of 50 kOe.
In a zero-applied magnetic field, below TN = 33 K and down to TmND = 15 K Tb3Ni2Ge3 shows an ac-antiferromagnetic ordering with the C2'/c magnetic space group, a K0 = [0, 0, 0] propagation vector and a aTb3Ni2Ge3 x bTb3Ni2Ge3 x cTb3Ni2Ge3 magnetic unit cell. Below TmND = 15 K, its magnetic structure is a sum of the ac-antiferromagnetic component with the C2'/c magnetic space group of the K0 vector and a sine-modulated a-antiferromagnetic component of the K1 = [0, 0, 1/3] propagation vector (the magnetic unit cell is aTb3Ni2Ge3 x bTb3Ni2Ge3 x 3cTb3Ni2Ge3). The magnetic structure is made from the 'Tb2 - 2Tb1' clusters of the Tb1 8f and Tb2 4c sublattices with a dominant role of the Tb2 sublattices in the magnetic ordering of Tb3Ni2Ge3.
Key words: Rare-earth compounds; Magnetic properties; Magnetocaloric effect; Neutron diffraction; Magnetic structure