First order magnetic phase transition in tetragonal NpCu2Si2

Magnetization and Np²³⁷ Mössbauer studies of the tetragonal compounds NpM₂Si₂ (M = Cr, Mn, Fe, Co, Ni, Cu) were performed. NpMn₂Si₂ is ferromagnetic. All other compounds order antiferromagnetically. Only in NpCu₂Si₂ the Mössbauer studies reveal a first order magnetic phase transition at T_N = 34 K. It is interpreted in terms of Blume's model, originally developed for cubic UO₂.     

Neutron diffraction studies of the magnetic ordering in the rare earth compounds TbNi2Si2, HoCo2Si2 and TbCo2Si2

Neutron diffraction studies and magnetic measurements on the compounds TbNi₂Si₂ (1), HoCo₂Si₂ (2) and TbCo₂Si₂ (3) revealed a collinear antiferromagnetic order below T_N = 10 ± 1 K (1), T_N = 13 ± 1 K (2) and T_N = 30 ± 2 K (3) with the rare earths moments oriented along the c-axis [m₀ = 8.8 ± 0.2 μ_B (1), m₀ = 8.1 ± 0.2 μ_B (2), m₀ = 8.8 ± 0.2 μ_B (3)] and the corresponding wavevector are $\text{k}\text{= [}\text{1}\text{2}\text{1}\text{2}\text{0] (1)}\text{and}\text{k}\text{= [ 0 0 1] (2) (3)}$. The magnetic structure of the compounds HoCo₂Si₂ and TbCo₂Si₂ consists of ferromagnetic layers perpendicular to the c-axis coupled antiferromagnetically (+?+?) while for TbNi₂Si₂ the ordering within (0 0 1) plane is antiferromagnetic and the planes (0 0 1) are indeed decoupled.     

Neutron diffraction study of RECo2Si2 intermetallics

A neutron diffraction study of polycrystalline RECo₂Si₂ intermetallics (RE = Pr, Nd, Tb, Ho, Er) carried out at liquid helium temperature shows the presence of a collinear antiferromagnetic ordering of +?+? type. Magnetic moment is localized on RE ions only and amounts to the RE³⁺ free ion value. In ErCo₂Si₂ the magnetic moment is normal to the tetragonal unique axis, whereas in the remaining compounds the magnetic moment is aligned along it. Néel points were determined from the temperature dependence of magnetic peak heights.     

Neutron diffraction study of magnetic ordering in ErMn2Si2, ErMn2Ge2 and ErFe2Si2

Neutron diffraction study of polycrystalline compounds ErMn₂Si₂, ErMn₂Ge₂ and ErFe₂Si₂ was performed in the temperature range between 1.8 and 293 K. All compounds have tetragonal, ThCr₂Si₂-type crystal structure. The antiferromagnetic collinear structure of ErMn₂Si₂ and ErMn₂Ge₂ at both RT and LNT, consists of a sequence + - + - of ferromagnetic layers of Mn atoms. The magnetic moment of an Mn atom (≈2μ_B) is parallel to the c-axist. At low temperatures (LHT and lower), the ferromagnetic ordering within the Er sublattice is observed. The magnetic moment (μ_Er ≈ 9μ_B) is perpendicular to the c-axis. From the temperature dependence of the intensities of the magnetic peaks, the following values for the Curie temperatures were obtained: (10±5) K for ErMn₂Si₂ and (8.5±3) K for ErMn₂Ge₂. For ErFe₂Si₂ a collinear antiferromagnetic structure of the + - - + type was found, the magnetic unit cell consisting of the chemical one, doubled along the c-axis.     

Neutron diffraction determination of the magnetic phases of CoCl2·2H2O

The metamagnetic behaviour of CoCl₂·2H₂O has been determined by means of neutron diffraction. At T = 4.2 K the reflections of the antiferromagnetic zero-field phase disappear, when a magnetic field of H_c1 = 31.8 kOe is applied along the b axis. The new ferrimagnetic phase vanishes at H_c2 = 46.1 kOe and the magnetically saturated configuration is reached. The three phases meet at a triple point at T_T = 8.9 K and H_T = 37.5 kOe. Two types of phase transition have been detected.     

Neutron diffraction determination of the magnetic phases of FeCl2·2H2O

The metamagnetic behaviour of FeCl₂·2H₂O has been determined. At T = 4.2 K the reflections of the antiferromagnetic zero-field-phase dissapear, when a magnetic field of H₁ = 39 kG is applied along the direction of sublattice magnetization. There is evidence for a ferrimagnetic phase with a unit cell in which the a axis is tripled. At H₂ = 46 kG this phase vanishes, and the magnetically saturated configuration is reached. As the temperature is increased, the three phases meet at a triple point at T_T = 11.7K and H_T = 42.0 kG.     

Neutron diffraction studies of Tb2Rh3Si5 compound

In this work neutron diffraction studies of Tb₂Rh₃Si₅ compound are reported. The compound crystallizes in the monoclinic crystal structure of Lu₂Co₃Si₅-type. At 1.5 K an antiferromagnetic ordering with a propagation vector k=(1/2;1/2;1/2) was observed. The Tb magnetic moments of 9.8(2) μ_B form a non-collinear magnetic structure. In the vicinity of Néel temperature of 8 K a change of the magnetic ordering is evidenced. The change seems to be connected with phase transition from commensurate to incommensurate sine-wave modulation of the Tb magnetic moments.     

Neutron diffraction determination of the magnetic structure of Dy PO4

Dy PO₄ is antiferromagnetically ordered below 3.39 K. The spin-structure is described by an antiparallel arrangement of nearest neighbours along the crystallographic c-axis. The magnetic moment at 1.8 K is (9.0±0.3) μ_β. These results confirm that Dy PO₄ may be considered as an ideal three-dimensional Ising system.     

Magnetic structures of PrCO2Si2 and TbCo2Si2 compounds

Neutron diffraction studies of polycrystalline PrCo₂Si₂ and TbCo₂Si₂ compounds were carried out at 4.2 and 293 K. Both samples have collinear antiferromagnetic order below T_N(31(1) and 46(1) K for Pr and Tb compound respectively), with their magnetic moments parallel to the c axis. The ordered magnetic moment values of Pr and Tb at 4.2 K (3.19 and 9.12 μ_B respectively), are close to the saturation value of the free ions. The corresponding magnetic space group P_l4/mnc (Sh⁴¹⁰₁₂₈) is body-anticentered ($\text{k =}\text{111}\text{222}$ refering to P_l cell).     

Neutron diffraction study of magnetic ordering in PrCu2Si2, PrCu2Ge2, PrFe2Ge2 and NdFe2Ge2

A neutron diffraction study of polycrystalline PrCu₂Si₂ [1], PrCu₂Ge₂ [2], PrFe₂Ge₂ [3] and NdFe₂Ge₂ [4] intermetallics carried out at liquid helium temperature shows the presence of a collinear antiferromagnetic order below T_N = 19 ± 1 K [1], T_N = 16 ± 1 K [2], T_N = 9 ± 1 K [3] and 13 ± 1 K [4]. Magnetic moment, parallel to the c-axis is localized on RE ions only. The magnetic structure of these compounds consists of ferromagnetic layers perpendicular to the c-axis coupled antiferromagnetically with sequence +-+- for PrCu₂Si₂ and PrCu₂Ge₂ and +--+ for PrFe₂Ge₂ and NdFe₂Ge₂. The RE moments amount close to the free ion values for Fe containing compounds but are smaller in those containing Cu suggesting a fairly strong influence of crystal field.     

Neutron diffraction study of magnetic properties of TmCo2

The present neutron diffraction studies have confirmed that TmCo₂ represents an exception within the RCo₂ series. It was found that, in contrast with other heavy RCo₂ compounds, the Co sublattice in TmCo₂ does not order magnetically below the Curie temperature (T_c = 3.9 K). This is assumed to be due the fact that in TmCo₂ the intersublattice (f-d) molecular field is smaller than the critical field necessary to induce magnetic order within the Co sublattice, as is the case in other RCo₂ compounds. Furthermore, we show that the magnetic structure and the onset of long-range order in TmCo₂ depend sensitively on the sample preparation, which partly explains the differing results published earlier.     

Neutron and X-ray diffraction studies on the Tb2Ni3Si5 single crystal

Neutron and X-ray diffraction studies on the Tb₂Ni₃Si₅ single crystal have been done to investigate its crystal modulation and magnetic properties. The modulated single crystal is constructed by the TbNiSi₂ (CeNiSi₂-type Cmcm) and the Tb₂Ni₃Si₅ (U₂Co₃Si₅-type Ibam) lattices. The relationship between the two lattices is described as direction of the b₁₁₂-axis coincides with the a₂₃₅-axis. The crystal modulation gives significant effects on magnetism. Each of the two lattices takes complex antiferromagnetism with multiplex propagation vectors.     

The magnetic structure of HoCo2Si2

We have carried out neutron diffraction on a HoCo₂Si₂ powder sample at 4.2 K. The magnetic structure of this compound is collinear antiferromagnetic with the holmium magnetic moments parallel to the c-axis of the crystal. The magnetic moment value of holmium is 9.85 μ_B. The magnetic space group is I4/mm'm' (Sh⁴¹⁰₁₂₈) k = 000 The ordering temperature is t_n = 12(1) K.     

Neutron diffraction study of DyCu2Ge2

The DyCu₂Ge₂ compound was studied by neutron diffraction on the Grenoble Nuclear Research Center multicounter system. The compound is isostructural to the rare earth RCu₂Ge₂ compounds with space group I4/mmm. 19 superlattice lines were observed in the 3 K pattern which are consistent with a doubling of the unit cell in the a and c directions. The moment value is 8 μ_B making an angle of 30° with a and 70° with c axis. The structure consists of ferromagnetic (1 0 1) layers with antiferromagnetic coupling between them. The Néel and Curie paramagnetic temperature of this compound is 8 K and ? 15 K respectively.     

Neutron diffraction study of the magnetic structure of Er0.75 Lu0.25

Neutron diffraction studies of an Er_0.75 Lu_0.25 alloy single crystal show a transition to a c-axis longitudinal spin wave at 68 K and a transition to a slightly distorted antiferromagnetic conical structure at 40 K. No ferromagnetic transition has been observed down to 4.9 K.     

Neutron diffraction study of the magnetic ordering in EuAs3

The magnetic structure of one of the two ordered phases has been determined at 5 K. The magnetic structure is found to be antiferromagnetic with a cell doubling in the c direction of the monoclinic nuclear cell. The centering in the nuclear cell is replaced by anticentering. The collinear magnetic moments are parallel to the b axis. The magnetic moment per Eu atom has been found to be 5.74(6)μ_B which leads to the saturation magnetic moment of 6.5μ_B.     

Crystal structure and magnetic properties of HoPt2Si2

The crystal structure of HoPt₂Si₂ was determined using powder neutron diffraction data. It is tetragonal, CaBe₂Ge₂ type (space group P4/_n mm). Neutron diffraction and magnetometric measurements indicate that HoPt₂Si₂ remains paramagnetic at the temperature of 2.0 K.     

The antiferromagnetic structure of ErCo2Si2 by neutron diffraction

The magnetic structure of the tetragonal ErCo₂Si₂ compound is determined by neutron diffraction on powder sample at 4.2 K. The magnetic ordering is connected with a symmetry lowering, magnetic space group P_2s$\text{1}$ (Sh⁷₂)k = 000. The structure is collinear antiferromagnetic with the erbium magnetic moments making an angle of 56.2° with the c axis. The magnetic moment value for erbium is 6.75μ_B.     

Neutron diffraction and magnetic measurements of polycrystalline NH4MnCl3

Neutron diffraction and magnetic susceptibility measurements show NH₄MnCl₃ to be an antiferromagnet of type G with T_N ∼ 105°K. The low temperature patterns reveal a tetragonal splitting and superlattice lines which were accounted for by assuming the space group to be P bnm.