The magnetic structure of U2N2Te

The magnetic structure of tetragonal U₂N₂Te has been studied by means of neutron diffraction on polycrystalline sample. A ferromagnetic alignment of the magnetic moments below 68 K has been confirmed. The best agreement between the calculated and observed intensities of the magnetic reflections has been obtained for the moment direction forming an angle 70 ± 5° to the tetragonal axis. The magnitude of the uranium ordered moment was found to be 2.50 ± 0.05 μ_B.     

CRYSTALLOGRAPHIC STRUCTURE AND INTRINSIC MAGENTIC PROPERTIES OF R2Fe14BNx

We found that the nitrogen atoms can enter into the R₂Fe₁₄B structure by a proper heat treatment in nitrogen atmosphere. The crystallographic structure and magnetic properties of R₂Fe₁₄BN_x, R =Nd and Y, have been investigated by using X-ray and neutron diffraction techniques as well as magnetic measurements. The neutron diffrac-tion data show that the nitrogen atoms occupy the 4f interstices. The interstitial nitrogen atoms were found to have an effect of enhancing Curie temerature, whereas, decreasing saturation magnetization and magneto-crystalline anisotropy. The rela-tionship of the crystal structure and the intrinsic magnetic properties of this crystal is discussed.     

On the ground-state magnetic structure in Er2Ni2Pb

We have studied the unusual low-temperature magnetic phase of Er₂Ni₂Pb using powder neutron diffraction measurements in zero field down to 460 mK. Our previous neutron diffraction experiments down to 1.5 K showed that magnetic Bragg reflections seen in Er₂Ni₂Pb can be indexed by several propagation vectors that partially coexist. All the incommensurate propagation vectors seemed to disappear in the low temperature limit. The present study, however, shows that reflections belonging to the propagation vector q’ = (0.47 0 1/2) do not disappear but remain present down to 460 mK. This highly unexpected result suggests that the magnetic structure described by this propagation vector might not be a simple sine-wave modulation. One interesting possibility here is a spin-slip structure as the ground state.     

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.     

Direct evidence for the magnetic ordering of Nd ions in NdMn2Si2 and NdMn2Ge2 by high resolution inelastic neutron scattering

We have investigated the low energy nuclear spin excitations in NdMn₂Si₂ and NdMn₂Ge₂ by high resolution inelastic neutron scattering. Previous neutron diffraction investigations gave ambiguous results about Nd magnetic ordering at low temperatures. The present element-specific technique gave direct evidence for the magnetic ordering of Nd ions. We found considerable difference in the process of the Nd magnetic ordering at low temperature in NdMn₂Si₂ and NdMn₂Ge₂. Our results are consistent with those of magnetization and recent neutron diffraction measurements.     

Magnetic properties of the Ce1-xLaxMn2Si2 system

Magnetic properties of the Ce_1-xLa_xMn₂Si₂ system were investigated by means of neutron diffraction and magnetometry. The samples with low La concentration (x?0.5) have antiferromagnetic properties. A transition from an antiferromagnetic to a ferromagnetic state can be observed for x=0.6 (for increasing temperature). More La leads to the samples being ferromagnetic. A collinear magnetic structure is seen from the neutron diffraction spectra. From all the results known up to now it follows, that type of magnetic ordering, i.e. antiferro- or ferro-depends on the Mn-Mn interatomic distances in the basal plane.     

Critical behaviour of Mn1.11Al0.89 alloys

The diffraction maxima (001) and (100) of the Mn_1.11Al_0.89 alloy have been measured by the neutron powder diffraction method in the temperature range from 23 to 427 C. The Curie temperature is found to be (404 ±2)°C. Temperature dependence of the magnetic structure factor gave the critical exponent β = 0.31±0.02.The disorder parameter has been found to decrease with the temperature. A convenient expression describing this behaviour has been proposed and discussed.     

Structural and magnetic properties of Sc1.1Fe3.9Al8 alloy

The crystallochemical and magnetic nature of ternary Sc_1+δFe_4−δAl₈ intermetallic with a small Sc excess δ=0.1 was investigated by scanning electron microscope, X-ray powder diffraction, neutron diffraction, Mössbauer effect and superconducting quantum interference device techniques. The sample crystallizes in a tetragonal ThMn₁₂ type structure. The excess of Sc atoms substitute Fe at the (8f) positions and have a pronounced effect on the magnetic properties. The experiments carried out in temperature range 4-320 K show that below 120 K the magnetic structure of the alloy forms a double cycloid with magnetic moments rotating according to the incommensurate in-plane wave vector, which is temperature independent up to 160 K. The value of Fe magnetic moment is close to 0.9 μ_B atom⁻¹ at 4 K. Temperature dependence of unit cell dimensions can be explained within the Debye-Grüneisen approximation.     

Crystal and magnetic structure of Ho2NiGe6

The crystal and magnetic structure of Ho₂NiGe₆ was studied by powder neutron diffraction. The paramagnetic neutron diffraction data confirmed the Ce₂CuGe₆-type crystal structure reported earlier for this compound. Below the Néel temperature equal to 11 K the Ho magnetic moments form a uniaxial antiferromagnetic ordering. The Ho magnetic moments equal to 8.16(7)μ_B at 1.5 K are parallel to the b-axis. The data are compared with those published for HoNi_0.46(6)Ge₂.     

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.     

Low temperature thermodynamical properties of ErCu2Si2

ErCu₂Si₂ crystallises in the tetragonal ThCr₂Si₂-type crystal structure. In this paper results of magnetometric, electrical transport, specific heat as well as neutron diffraction are reported. Results of electrical resistivity and specific heat measurements performed at low temperature yield existence of magnetic ordering roughly at 1.3 K. These results are in concert with neutron diffraction measurements, which reveal simple antiferromagnetic ordering between 0.47 and 1.00 K. At temperatures ranging from 1.00 up to 1.50 K an additional incommensurate magnetic structure was observed. The propagation vector k=(0;0;0.074) was proposed to describe magnetic reflections within the amplitude modulated magnetic structure. Basing on specific heat studies the crystal field levels splitting scheme and magnetic entropy were calculated.     

Evidence for the helical spin structure due to antisymmetric exchange interaction in Cr13NbS2

It is pointed out that the helical spin structure due to antisymmetric exchange interaction can be distinguished from the one of usual origin by observing its behavior under the external magnetic field. This type of helical structure is shown to be realized in Cr_{$\text{1}\text{3}$}NbS₂ from analyses of magnetic and neutron diffraction measurements.     

Magnetic ordering in the garner NaCa2Mn2V3O12

The magnetic structure of the garnet NaCa₂Mn₂V₃O₁₂ with Mn²⁺ ions at 16a positions has been determined by neutron diffraction. Also measurements of Young's modulus and the inverse susceptibility have been made. The magnetic ordering is the same as in the corresponding Co, Ni, Cr-garnets.     

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.     

Crystals and magnetic structure of RMn2Si2 (R = Pr, Nd, Y) and YMn2Ge2

Crystallographic and magnetic properties of PrMn₂Si₂, NdMn₂Si₂, YMn₂Si₂ and YMn₂Ge₂ intermetallics were studied by X-ray, neutron diffraction and magnetometric measurements. The crystal structure of all four compounds was confirmed to be body-centered tetragonal (space group I4/mmm). All were found to be antiferromagnetic with Néel points at 368, 380, 460 and 395 K respectively. Neutron diffraction results indicate that their magnetic structure consists of ferromagnetic layers composed of Mn ions piled up along the c-axis. Each layer is antiferromagnetically coupled to adjacent layer. The magnetic space group is I_p4/m′m′m′. No magnetic ordering of the R sublattice was observed at 1.8 K in the case of R = Pr and Nd.     

Magnetic dimensionality of Y(2−x)DyxBaCuO5

In this communication, we report the effect that doping Y₂BaCuO₅ with Dy has on its two-dimensional (2D) magnetic structure. Pure samples at both ends of the series, as well as samples doped with 1, 5, 10 and 25% dysprosium, have been characterised using X-ray diffraction, and AC susceptibility together with neutron diffraction studies on the 1 and 5% samples, which were used to measure the magnetic ordering at low temperatures. The results show that 1% Dy is enough to disrupt the 2D magnetic ordering turning it into a 3D array. The low dysprosium concentration indicates that the 3D ordering is achieved without the existence of a rare earth magnetic sublattice. The change in the ordering temperature from 27 K for the pure Y₂BaCuO₅ to 16 K for the 1 and 5% Dy compounds, together with the parameters from the AC susceptibility fittings, reveal that the effect of the Dy doping affects the electronic structure of the Cu ions that become involved in the superexchange pathways. The discrepancy between the parameters obtained by the Curie-Weiss fittings of the real part of the AC susceptibility and the neutron diffraction results, shows that the exchange mechanism deviates from the mean field model for all dysprosium concentrations.     

Magnetic ordering and low-temperature thermodynamic properties of ErFe2Ge2

Polycrystalline sample of ErFe₂Ge₂ was investigated by means of magnetic susceptibility, heat capacity and electrical resistivity measurements, as well as by powder neutron diffraction. All these experiments yielded an evidence of magnetic ordering setting at about 3 K. The low-temperature neutron data revealed the formation of a sine-modulated commensurate antiferromagnetic structure characterized by the propagation vector k=(0, 0, ). The erbium magnetic moment is aligned parallel to the crystallographic a-axis. At T=1.55 K it is equal to 7.06(5) μ_B.     

Magnetic properties of UT2Si2 and UT2Ge2 (T = Co,Ni, Cu) intermetallic systems

Neutron diffraction and magnetization measurements indicate that, at low temperatures, long-range magnetic order is present in UCO₂Si₂, UNi₂Si₂, UCu₂Si₂, UNi₂Ge₂, and UCo₂Ge₂. UCo₂Si₂ and UNi₂Ge₂ are simple collinear antiferromagnets of +-+- type, UCu₂Si₂ a simple collinear ferromagnet. In UNi₂Si₂, a magnetic phase transition from a LSW type structure to collinear antiferromagnetism of +-+- type was found, while in UCu₂Ge₂, the antiferromagnetic structure of ++-- transforms into collinear ferromagnetism. Crystal structure and magnetic parameters are given. No magnetic moment on transition metal ions was found within the accuracy of a powder neutron diffraction experiment. The stability of particular magnetic ordering schemes is discussed in terms of an isotropic RKKY mechanism.     

Magnetic ordering in La0.75Sr0.25CrO3: A neutron diffraction study

Low-temperature neutron diffraction measurements were carried out on a powder sample of the compound La_0.75Sr_0.25CrO₃ in order to elucidate its magnetic structure. Rietveld analysis of the neutron diffraction data, as a function of temperature, showed that it possesses a G-type antiferromagnetic alignment of Cr spins at all temperatures below 300 K. Down to the lowest achievable temperature, viz. 17 K, the Cr site moments were found to be the weighted average of the 75% Cr³⁺ and 25% Cr⁴⁺ spin-only ionic moments. At 17 K, the Cr site moment was 2.71(5) μ_B/Cr ion. There is no observable change in the Cr–O bond lengths as a function of temperature. The tilt angles of the CrO₆ octahedra marginally increase with decreasing temperature.     

Reinvestigation of the magnetic structure of Ca3Mn2Ge3O12

Precise neutron diffraction experiments performed on powdered antiferromagnetic garnet Ca₃Mn₂Ge₃O₁₂ lead to a complex non collinear magnetic structure. In the absence of magnetic field, it is three dimensional with eight spin directions and belongs to ¹I_41/a. At a critical magnetic field spin-flop mechanism occurs with a lowering of the magnetic symmetry which becomes triclinic. In addition to tetragonal anisotropy, both single ion orthorhombic anisotropy and its antisymmetrical counterpart for definite pairs of ions are required to explain both the observed structure and its behaviour in a magnetic field.