Magnetic ordering of Hf3Ni2Si3-type {Sm, Tb, Er}3Co2Ge3 and {Tb, Ho}3Ni2Ge3 compounds

Abstract

The magnetic ordering of Hf3Ni2Si3-type {Sm, Tb, Er}3Co2Ge3 and {Tb, Ho}3Ni2Ge3 compounds (space group Cmcm, oC32) was investigated via magnetization measurements and neutron diffraction study in a zero-applied field. {Sm, Tb, Er}3Co2Ge3 and Ho3Ni2Ge3 exhibit field sensitive complex antiferromagnetic orderings with TN=51K, Tm=10K for Sm3Co2Ge3, TN=34K, Tm=13K for Tb3Co2Ge3, TN=7K for Er3Co2Ge3 and TN=11K for Ho3Ni2Ge3. At 2K and above the critical field of ~5kOe, 20kOe, 4kOe and 7kOe for Sm3Co2Ge3, Tb3Co2Ge3, Er3Co2Ge3 and Ho3Ni2Ge3, respectively, saturation magnetizations per rare-earth atom are 6.5μB for Tb3Co2Ge3, 7.0μB for Er3Co2Ge3 and 8.0μB for Ho3Ni2Ge3 in the field of 140kOe, whereas magnetization of Sm3Co2Ge3 has an antiferromagnetic behaviour. The isothermal magnetic entropy change, ΔSm, indicates a field-induced ferromagnetic ordering in Sm3Co2Ge3, Tb3Co2Ge3, Er3Co2Ge3 and Ho3Ni2Ge3 with a maximal ΔSm value of −10.9J/kgK for Ho3Ni2Ge3 at 11K for a field change of 50kOe.In a zero-applied magnetic field, below TN=33K and down to TmND=15K Tb3Ni2Ge3 shows an ac-antiferromagnetic ordering with the C2′/c magnetic space group, a K0=[0, 0, 0] propagation vector and a aTb3Ni2Ge3×bTb3Ni2Ge3×cTb3Ni2Ge3 magnetic unit cell. Below TmND=15K, 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×bTb3Ni2Ge3×3cTb3Ni2Ge3). 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.