M. Kolenda

Neutron diffraction investigation of long-range magnetic ordering in TbCu2Si2 and HoCu2Si2

Abstract The magnetic structures of TbCu 2 Si 2 and HoCu 2 Si 2 were determined by neutron diffraction. The crystal structure of both compounds is of the ThCr 2 Si 2 type, space group 14/mmm. The magnetic unit cell at 4.2 K is described by a wavevector k = ( 1 2 , 0, 1 2 ). The Shubnikov space group is triclinic P a 1(Sh 2 ). The magnetic order can be described as ferromagnetic (101) layers stacked antiferromagnetically with moments on rare-earth ions perpendicular to the c -axis.

Incommensurate magnetic ordering in TbOs2Si2, HoOs2Si2 and ErOs2Si2

Abstract Neutron diffraction and magnetometric measurements were performed on polycrystalline samples of TbOs 2 Si 2 , HoOs 2 Si 2 and ErOs 2 Si 2 . All were found to exhibit at low temperatures an incommensurate longitudinal static magnetization wave with moments along the c -axis and propagation along the b -axis in the case of TbOs 2 Si 2 and HoOs 2 Si 2 , but with moments and propagation along the b -axis in the case of ErOs 2 Si 2 . Magnetometric measurements done at 4.2 K for TbOs 2 Si 2 and HoOs 2 Si 2 indicate that both become ferromagnetic at critical magnetic fields of 10 and 2 kOe, respectively.

Magnetic transition in TbMn2Si2

Abstract TbMn2Si2 (ThCr2Si2-type crystal structure) exhibits at 1.6 K two ferromagnetic sublattices composed of Tb1− and Mn2− magnetic moments directed along thec-axis; their magnitudes at 1.6 K are 8.7(1) and2.4(1)μR respectively. The sublattices are oriented antiferromagnetically. The Tb sublattice becomes disordered at 100 K: the Mn sublattice starts to transform into an antiferromagnetic structure at 100 K and is stable with2.4(1)μR moment up to the Neel point at 501 K.

Magnetic structure and phase transition in TbPdSn compound

Abstract The compound TbPdSn, with orthorhombic symmetry and TiNiSi-type structure, space group Pnma (D 16 2h ), orders antiferromagnetically at T N = (19±1) K. It orders at T N with a sine-wave-modulated magnetic spin arrangement with wavevector k = (0, 0.25, 0). Below T S = 10 K the low-temperature magnetic structure is characterized by propagation vector k = (0, 0.25, 0.075) and the magnetic moment forms an antiferromagnetic cone spiral. The experimentally determined magnetic structures are in agreement with those proposed by symmetry analysis.

Antiferromagnetic ordering in PrCu2Si2, PrCu2Ge2 and TbCuSi2

Abstract Magnetic and neutron diffraction data collected for polycrystalline samples of PrCu 2 Si 2 , PrCu 2 Ge 2 and TbCu 2 Si 2 show that the compounds are collinear antiferromagnets. The neutron diffraction data, unlike the magnetic data, do not show any magnetic phase transition in the magnetic ordered state.

X-ray and neutron diffraction studies of UPdSn

Abstract Crystal structure and magnetic interactions in the ternary compound UPdSn have been investigated by means of X-ray and neutron diffraction measurements. In accordance with previous reports, except for the antiferro-paramagnetic transition at T N ≈ 40 K, there is also a magnetic phase transition at approximately 25 K, first noted in the magnetic susceptibility behaviour. The magnetic structure with decreasing temperature is thought to be associated with the rotation of the magnetic moment away from both the z and y axes. The occurrence of the non-collinear magnetic structure implies a crystal structure distortion of the hexagonal unit cell into an orthorhombic one at T N , which becomes much stronger with decreasing temperature. X-ray diffraction patterns obtained at T = 23 and 10 K are in accordance with the assumption that another monoclinic distortion takes place in the low temperature region. This is consistent with Robinson et al. and our neutron diffraction investigations. At T = 25 K a remarkable change in the value of the ordered moment of uranium, μ, has been observed. The value of μ at the lowest measured temperature 2 K was found to be 2.20(5)μ B , while at T = 30 K it decreases to 1.42(10)μ B . At temperatures below 30 K the ac-susceptibility points to the coexistence of long-range order with some kind of spin-glass-like behaviour.

Low temperature neutron diffraction study of the CeFe2Al8 compound

Abstract Powder neutron diffraction measurements of the CeFe 2 Al 8 compound at 1.5, 10 and 75 K indicate that this compound crystallizes in an orthorhombic crystal structure (space group Pbam ). The crystal structure parameters of CeFe 2 Al 8 were determined. The low temperature data at T =1.5 K did not reveal magnetic ordering. The magnetization, magnetic susceptibility and the Mossbauer effect data indicate the existence of clusters of iron atoms below 6.5 K.

Incommensurate magnetic structures in TbRhGe

TbRhGe, which exhibits the TiNiSi-type crystal structure orders antiferromagnetically below 23 K. At 1.7 K its magnetic structure is described by a sine-modulated spin wave with a wave vector k = [0, 0.45, 0.11]. At 18 K it transforms into a magnetic structure represented by the wave vector k = [0, 0.44, 0]. The magnetic moment localized on terbium amounts to 7.6(1) Bohr magnetons at 1.7 K and is aligned along the a-axis of the orthorhombic TiNiSi-type unit cell in both magnetic structures.

Incommensurate magnetic ordering in CePtSn and TbPtSn

Abstract The crystal and magnetic structures of CePtSn and TbPtSn were determined by neutron diffraction on polycrystalline samples. Both compounds exhibit the orthorhombic TiNiSi-type of crystal structure and order antiferromagnetically below 7.8 K (CePtSn) and 13.8 K (TbPtSn). In CePtSn a sine modulated magnetic ordering described by the propagation vector k = (0, 0.428, 0) has been found at 1.7 K. In TbPtSn the magnetic structure at 1.7 K is also sine modulated and is characterized by the wave vector k = (0, 0.300, 0.059). It transforms at 10 K into a structure with the wave vector k = (0, 0.275, 0). The magnitudes of the magnetic moments at 1.7 K localized on cerium and terbium ions are determined to be 0.97(5) and 9.06(5)μB respectively.

Crystal and magnetic structure of TbNiGe and DyNiGe compounds

Abstract The results of X-ray neutron diffraction and magnetometric measurements for TbNiGe and DyNiGe compounds are presented. Both compounds crystallize in an orthorhombic TiNiSi-type crystal structure and are antiferromagnets with Neel temperature of 18 and 6 K, respectively. At low temperatures both compounds have square modulated structures with a wave vector k = ( 2 3 , 1 3 , 0) . With increase in temperature a change to a sinusoidally modulated structure for TbNiGe and probably a cycloidal spiral structure for DyNiGe is observed. In both structures and both phases the magnetic moments are parallel to the c -axis. In the case of the TbNiGe compound a coexistence of two magnetic structures over a wide temperature range is observed. The experimentally determined magnetic structures are in agreement with those proposed by symmetry analysis.