Magnetic properties of NdCo2Ge2, ErCo2Ge2 and PrFe2Ge2 compounds

Magnetometric and neutron diffraction studies of polycrystalline NdCo₂GE₂, ErCo₂Ge₂ and PrFe₂Ge₂ compounds were carried out in the temperature range between 4.2 and 300 K. All samples are antiferromagnetic with Néel temperature 26.5, ～ 4.2 and 13 K, respectively. The RECo₂Ge₂ compounds have collinear antiferromagnetic order of +?+? type. For PrFe₂Ge₂ a sinusoidal magnetic structure is observed. Magnetic moment is localized on RE atoms only and is equal to that of RE³⁺ free ion value. In ErCo₂Ge₂ the magnetic moment of Er atoms is perpendicular to the c-axis, whereas for remaining compounds it is parallel to the c-axis.     

The antiferromagnetic structures of TbCu2Ge2 and HoCu2Ge2 by neutron diffraction

The magnetic structures of TbCu₂Ge₂ and HoCu₂Ge₂ were studied by neutron diffraction. At 293 K the chemical structure is tetragonal body centered, space group I 4/mmm. The magnetic cell at 4.2 K is four times larger than the chemical one with a wave vector $\text{k =}\text{1}\text{2}\text{0}\text{1}\text{2}$. The magnetic space group is triclinic P_a$\text{1}$(Sh₂⁷) for both compounds. The moment values and directions are μ_Tb = 8.48(6) [μ_B] along [110] tetr. and μ_HO = 6.5(1)[μ_B] making an angle of 81.4(°) with c and 80(°) with a₁. The structure consists of ferromagnetic (101) layers stacked antiferromagnetically.     

Magnetic structure of the Sm5Ge4-type Tb2Ti3Ge4

The orthorhombic Sm₅Ge₄-type Tb₂Ti₃Ge₄ shows square modulated non-collinear magnetic ordering with wave vector K=[±1/3, 1/2, 1/2] at 2 K. The terbium magnetic moments lie in the bc plane and magnetic moment value of 7.5(2) μ_B/Tb is obtained at 2 K.     

The squared modulated magnetic structure of HoRu2Ge2

The holmium ions order antiferromagnetically in the ternary tetragonal compound HoRu₂Ge₂, at the Néel temperature T_N = 20 K. This compound exhibits a squared modulated structure with a propagation vector k = [0.2216, 0.0111, 0.0] with a holmium magnetic moment of 6.6μ_B, parallel to the c-axis of the crystal. Crystal field calculation show that the tetragonal axis of HoRu₂Ge₂ is the easy axis.     

NdNi2Ge2化合物的结构和电磁输运性质

利用非自耗真空电弧熔炼法制备了NdNi₂Ge₂化合物样品,采用X射线粉末衍射技术和Rietveld全谱拟合分析方法测定了其晶体结构. 结果显示该化合物的空间群为I4/mmm,点阵参数为:a=4.120(1),c=9.835(0),Z=2,Nd原子占据2a晶位,Ni原子占据4d晶位,Ge原子占据4e晶位. NdNi₂Ge₂化合物呈现顺磁性,应用居里-外斯定律拟合计算得到居里-外斯常数为25.8,居里-外斯温度为6.24 K. 有效势磁矩为3.69μ_B,这与理论计算Nd³⁺的磁矩相符,表明磁矩主要源于Nd³⁺. 电阻率变化范围为0.3 Ω ·μm^-1-1 Ω ·μm,电阻曲线拟合显示NdNi₂Ge₂呈半金属性. 关键词： 2Ge₂')" href="#">NdNi₂Ge₂ Rietveld结构精修 电磁输运     

The antiferromagnetic structure of TbB4

The magnetic structure of the rare earth tetraboride TbB₄ (crystallographic space group P4/mbm) has been determined by neutron diffraction on a polycrystalline sample. Below the experimentally determined Néel temperature of T_N = (43±1) K TbB₄ is ordered antiferromagnetically. The data refinement yielded a magnetic moment value of (7.7 ± 0.2) μ_B/Tb ion at 4.2 K which we interpret as Tb⁴⁺. The magnetic structure is antiferromagnetic collinear with the moments perpendicular to the tetragonal axis.     

A powder neutron diffraction study of the ErCu2Ge2 compound - crystal field

The compound ErCu₂Ge₂ was studied by neutron diffraction. The diffraction diagram of this compound at 170 K agrees with its crystallographic structure. Its diagram at 1.9 K reveals the existence of superlattice lines consistent with a cell doubled in the a and c directions. The erbium magnetic moment (8.0±0.4)μ_B lies on the c-axis. Crystal field calculations on the Er³⁺ site give 7.9μ_B, with easy magnetization axis the c-axis of the crystal. Copper must contribute to the V^m_l crystal field parameters with a charge equal to 0.6⁺.     

Crystal structure,thermal expansion and magnetic properties of Nd2Cu0.8Ge3 compound

A new ternary intermetallic compound, Nd₂Cu_0.8Ge₃, was synthesized and its crystal structure was determined by Rietveld refinement of X-ray powder diffraction data. The Nd₂Cu_0.8Ge₃ compound crystallizes in space group I4₁/amd (No. 141), with a tetragonal a-ThSi₂ structure type, and a=0.41783(2) nm, c=1.43689(9) nm, Z=2 and D_calc=7.466 g/cm³. Using the high temperature powder X-ray diffraction (HTXRD) technique, the lattice thermal expansion behavior of the compound was investigated in the temperature range of 298–648 K, and the result shows that its unit-cell parameters increased anisotropically when temperature increased. The magnetic susceptibility measured in the temperature range of 5–300 K indicated antiferromagnetic order of Nd₂Cu_0.8Ge₃ at low temperatures, and the magnetic susceptibility can be well described over the range of 50–300 K using Curie–Weiss law. The calculated effective magnetic moment (μ_eff) is 3.53 μ_B and dominated by the contribution of the Nd³⁺ ions.     

Magnetic order in the ternary compound NdRu2Ge2

Heat capacity, electrical resistivity and neutron diffraction studies have been performed on the tetragonal ternary compound NdRu₂Ge₂. Between temperatures of 17 and 10 K, the compound exhibits two types of sine-wave modulated magnetic structures, having wave vectors k = (0.19, 0.05, 0.125) and k = (0.12, 0.12, 0.0) with the amplitude of the moment along the c axis. Below 10 K, a first-order transition occurs to a ferromagnetic state with a moment of 3.64(13)μ_B aligned along the tetragonal axis.     

Magnetic structure of the ternary germanide Ce3Ni2Ge7

The ternary germanide Ce₃Ni₂Ge₇ has been studied by means of neutron powder diffraction and Ce L_III X-ray absorption (XAS). This compound which orders antiferromagnetically below T_N=7.2(2) K, crystallizes in the orthorhombic (Cmmm space group) La₃Co₂Sn₇-type structure where Ce atoms occupying two inequivalent crystallographic sites: Ce1 at 2d site and Ce2 at 4i site. Below T_N, the antiferromagnetic structure of Ce₃Ni₂Ge₇ is collinear but only the Ce2 atoms carry a magnetic moment (1.98(2) μ_B at 1.4 K). The absence of ordered magnetic moment on Ce1 atoms can be correlated to the average valence v=3.03(1), determined by X-ray absorption spectroscopy, suggesting an intermediate valence state of cerium in the 2d site.     

Magnetic and hyperfine properties of NpFe2−xCoxSi2 tetragonal systems

Magnetization, ²³⁷Np Mössbauer effect and neutron diffraction studies of the tetragonal NpFe_2?xCo_xSi₂ (x = 0, 1, 1.5, 2) intermetallic compounds were performed. The Mössbauer studies of the²³⁷Np show a magnetic order below 87 (3)_, 15 (3), 37 (3), 42 (3) K, hyperfine fields of 2535 (50), 1600 (50), 2210 (50), 2600 (50) MHz and isometric shifts of -2.3 (3), +7.6 (3), 0 (3), -2.9 (3) mm/s (relative to NpAl₂), respectively. An extremely low magnetization of non-saturated character (at 4.2 K, 20 KOe) is observed.A polycrystalline ingot sample of NpCo₂Si₂ was studied by neutron diffraction at temperatures from 2 to 160 K. Five superlattice lines were observed at temperatures below 46 K and are consistent with an antiferromagnetic structure of the Np(2a) sublattice of type I with T_N = 46 (3) K. The Np ion magnetic moment consistent with the diffracted intensities is 1.5 (1) μ_B with no localized moment on the Co ion.A direct correlation between the Isomer shift, Hyperfine fields and ordering temperature is reported for the first time. This unusual correlation can be explained only if strong f-d, f-s hybridization are assumed.     

Magnetic phase transition in TbMn2Ge2

The crystal and magnetic stucture of TbMn₂Ge₂ are determined by neutron diffraction using a powder sample. The crystal structure of this compound is of the ThCr₂Si₂ type with small mixing of Mn and Ge atoms between 4(d) and 4(e) positions. At RT the antiferromagnetic collinear structure consist of a+?+? sequence of ferromagnetic layers of Mn atoms with the magnetic moment parallel to the c-axis. At 85 K, the ferromagnetic ordering within the Tb sublattice is observed. The magnetic moment (～7.7 μ_B) is parallel to the c-axis. At 4.2 K additional reflections are observed, which correspond to antiferromagnetic components in a monoclinic unit cell.     

Local and itinerant Magnetism AND Crystal structure of RRh2Ge2 and RRu2Ge2 (r = rare earth)

The compounds RRh₂Ge₂; and RRu₂Ge₂ were synthesized X-ray studies show that they have the expected ThCr₂Si₂; tetragonal-type structure Magnetization studies at 1 8–300 K, ¹⁵¹Eu Mossbauer studies at 4 l, 77 and 300 K and the crystallography studies show the following- All RRh₂Ge₂; like RRh₂Si₂; exhibit two magnetic phase transitions, one corresponding to the antiferromagnetic ordering of the local rare earth moments. T_N = 8–90 K, the other corresponding to the itinerant electron ordering of the Rh sublattice. T_M = 3–9 K The heavy rare earths in RRu₂G₂; order antiferromagnetically and undergo a spin-flop transition in a relatively low magnetic field, <10 kOe The light elements in RRu₂Ge₂; order in a ferromagnetic, somewhat unclear structure NdRu₂Ge₂, like NdRu₂Si₂, exhibits two peaks in the magnetization curves Again, the lower may correspond to itinerant electron ordenng or, alternatively, to spin reorientation of the rare earth sublattice Eu in both EuRh₂Ge₂ and EuRu₂Ge₂ is divalent, whereas Ce in both CeRh₂Ge₂ and CeRu₂Ge₂ is trivalent For all rare earths the ordenng transition in RRh₂Ge₂ is higher than in RRu₂Ge₂. This fact can be associated with the smaller R-R distances in RRh₂Ge₂ and/ or due to the stronger magnetic character of the Rh 4d conduction electrons Companson of the magnetic properties and ¹⁵¹Eu hyperfine interactions of Eu²⁺Rh₂Ge₂, Eu²⁺Ru₂Ge₂, Eu²⁺Rh₂Si₂ and Eu³⁺Ru₂Si₂ with all the other systems leads to the conclusion that the conduction electrons play the dominant role in determining the magnetic properties of these systems Crystal-field effects are also of considerable importance, since the Mossbauer studies yield for the second-order crystal-field parameter A⁰₂〈r²_4f〉 the huge values +385 and +282 K for EuRu₂Ge₂; and EuRh₂Ge₂, respectively The easy axis of magnetization in the Eu compounds is in the basal plane The large second-order crystal field predicts well the direction of the easy axis for all other rare earths No superconductivity has been observed in any of the compounds, down to 1 8 K A companson of the magnetic properties of the germanides with those of the silicides shows great similanties, the differences being accounted for by the different unit cell sizes and c/a ratios.     

Magnetic behaviour of NpAs2 from Mössbauer spectroscopy

The Mössbauer hyperfine spectra of the 60 keV resonance of ²³⁷Np in powder and single crystal absorbers of NpAs₂ were measured between 4.2 and 60 K. Below 18 K a simple magnetic plus quadrupole pattern is seen in accordance with a ferromagnetic spin structure in tetragonal NpAs₂. The isomer shift favors the 4+ charge state, the hyperfine field of 288 T implies a moment of 1.5μ_B at the Np ion. The large reduction compared to the free ion values points towards a strong mixing of the electronic ground state by crystalline field interactions. Above 18 K the spectrum changes into a complex hyperfine pattern indicating a sinusoidally modulated spin structure. Near 54 K a transition into the paramagnetic state is observed. Both magnetic transitions (18 and 54 K) exhibit a feature typical for a first-order character.     

Magnetization studies of TbFeO3

The spontaneous magnetization and principal magnetic susceptibilities of TbFeO₃ were measured from 4.2 to 300 K. The weak ferromagnetic moment is along the c crystallographic axis in the entire temperature range. The field dependence of the magnetization at 4.2 K was also studied. The magnetic behavior is interpreted in terms of an interaction between the ordered Fe³⁺ spin system and the electrons occupying the lowest lying “accidental” doublet of the Tb³⁺ ions. The FeTb interaction and the Tb³⁺ Van Vl eck susceptibility along the c axis play significant roles in determining the magnetic configuration of the Fe³⁺ spin system. No indication was found that the TbTb interaction plays a significant role in the magnetic behavior of TbFeO₃ at temperature above 4.2 K.     

237Np Mössbauer study of a novel intermetallic NpRh2Si2

NpRh₂Si₂ (ThCr₂Si₂ structure) has been studied by ²³⁷Np Mössbauer spectroscopy between 4.2 and 100 K. The isomer shift value suggest a Np⁴⁺ electronic configuration. A single site combined magnetic plus quadrupole pattern is observed up to the magnetic ordering temperature of T_c=73(1) K. A Np magnetic moment of 1.4μ_B is deduced from the hyperfine field measured at 4.2 K. The magnetic moments are estimated to make an angle of either 90° or 34° with the tetragonal axis.     

Magnetism and hyperfine interactions in EuM2Ge2 and GdM2Ge2(M = Mn,Fe, Co,Ni, Cu)

X-ray, magnetic susceptibility and ¹⁵¹Eu, ¹⁵⁵Gd Mössbauer effect studies of EuM₂Ge₂ and GdM₂Ge₂ were performed. All compounds crystallize in the ThCr₂Si₂ body centered tetragonal structure. In all compounds, except those with M = Mn and in EuM₂Ge₂, the M component carries no magnetic moment. All compounds except those with Mn are antiferromagnetic at low temperatures. In EuMn₂Ge₂ the Mn moments order ferromagnetically at 330 K and change to antiferromagnetic order when the Eu moments order ferromagnetically (9 K). This behaviour is different from that in GdMn₂Ge₂, where the Mn sublattice orders antiferromagnetically at 365 K and becomes ferromagnetic and antiparallel to the ferromagnetic Gd sublattice at 96 K. The Mössbauer studies of ¹⁵¹Eu and ¹⁵¹Gd provide values for the magnetic hyperfine fields, the quadrupole interactions and the orientation of the magnetic moments relative to the local fourfold axis (c-axis). It turns out that in the Eu compounds the easy axis of magnetization is close to the c-axis, while in the Gd compounds it is in the basal plane. In all systems, excluding those with Mn, the interatomic rare earth-rare earth distances have the dominant effect on the conduction electron charge density and polarization at the rare earth site and on the Curie point.     

Magnetic properties of the intermetallic compound Ce5Ge4

Magnetic and magnetocaloric properties of the compound Ce₅Ge₄ have been studied. This compound has orthorhombic Sm₅Ge₄-type structure (space group Pnma, no. 62) and orders ferromagnetically at ~12 K (T_C). The paramagnetic Curie temperature is ~−20 K suggesting the presence of competing ferromagnetic and antiferromagnetic interactions in this compound. The magnetization does not seem to saturate even in fields of 90 kOe at 3 K consistent with the presence of competing interactions. Saturation magnetization value (extrapolated to 1/H→0) of only 0.8μ_B/Ce³⁺ is obtained compared to the free ion value of 2.14μ_B/Ce³⁺. This moment reduction in the ordered state of Ce₅Ge₄ could be due to partial antiferromagnetic/paramagnetic ordering of the Ce moments and may also be due to crystalline electric field effects. Magnetic entropy change near T_C, calculated from the magnetization vs. field data, is found to be moderate with a maximum value of ~9 J/kg/K at ~11 K for a field change of 90 kOe.     

The magnetization of GdAl2

The magnetization of a single crystal of GdAl₂ has been measured parallel to the easy direction as a function of field (maximum field 1.7 T) within the temperature range 4.2–300 K. The main emphasis was placed on the results obtained for the ferromagnetic phase. From an analysis based on molecular field theory it is deduced that the magnetic moment at 0 K is 7.2 μ_B per Gd ion and that the molecular field cannot be represented by a simpler polynomial than λ₁M + λ₂M³ + λ₃M⁵. The same data is analysed using spin-wave theory from which it is deduced that the spin-wave stiffness is 18 meV Ų and that the conduction band susceptibility is approximately 2.6 x 10^-6 emu g^-1. The conduction electron polarization, parallel to the Gd ion moment, amounting to 0.2 μ_B per Gd ion implies the presence of an internal field acting on the conduction electrons of approximately 200 T at 0 K.     

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.