Search

The magnetic structure of the intermetallic compound ErGa has been determined using high‐resolution neutron powder diffraction. This compound crystallizes in the orthorhombic (Cmcm, No. 63) CrB‐type structure and orders ferromagnetically at 32 (2) K, with the Er moments initially aligned along the b axis. Upon cooling below 16 K, the Er magnetic moments cant away from the b axis towards the c axis. At 3 K, the Er moment is 8.7 (3) μB and the Er magnetic moments point in the direction 31 (3)° away from the crystallographic b axis, within the bc plane. 166Er Mössbauer spectroscopy work supports this structure and shows clear signals of the spin‐reorientation in both the magnetic and electric quadrupole hyperfine interactions. [ABSTRACT FROM AUTHOR]

Knowledge of magnetic symmetry is vital for exploiting nontrivial surface states of magnetic topological materials. EuIn2As2 is an excellent example, as it is predicted to have collinear antiferromagnetic order where the magnetic moment direction determines either a topological-crystalline-insulator phase supporting axion electrodynamics or a higher-order-topological-insulator phase with chiral hinge states. Here, we use neutron diffraction, symmetry analysis, and density functional theory results to demonstrate that EuIn2As2 actually exhibits low-symmetry helical antiferromagnetic order which makes it a stoichiometric magnetic topological-crystalline axion insulator protected by the combination of a 180∘ rotation and time-reversal symmetries: C 2 × T = 2 ′ . Surfaces protected by 2 ′ are expected to have an exotic gapless Dirac cone which is unpinned to specific crystal momenta. All other surfaces have gapped Dirac cones and exhibit half-integer quantum anomalous Hall conductivity. We predict that the direction of a modest applied magnetic field of μ0H ≈ 1 to 2 T can tune between gapless and gapped surface states. Magnetic symmetry is a vital factor to determine exotic topological phases. Here, Riberolles et al. demonstrate a helical antiferromagnetic order in EuIn2As2 which makes it a magnetic topological-crystalline axion insulator. [ABSTRACT FROM AUTHOR]

In the orthorhombic manganites o-RMnO3, where R is a heavy rare earth (R = Gd-Yb), the Mn3+ sublattice is known to undergo two magnetic transitions. The low temperature phase has an antiferromagnetic structure (collinear or elliptical), which has been well characterized by neutron diffraction in most of these compounds. The intermediate phase, occurring in a narrow temperature range (a few K), is documented for R = Gd–Ho as a collinear modulated structure, incommensurate with the lattice spacings. We report here on a 57Fe Mössbauer study of 2% 57Fe doped o-YbMnO3, where the spin only Fe3+ ion plays the role of a magnetic probe. From the analysis of the shape of the magnetic hyperfine Mössbauer spectra, we show that the magnetic structure of the intermediate phase in o-YbMnO3 (38.0 K < T < 41.5 K) is also modulated and incommensurate. [ABSTRACT FROM AUTHOR]

Nd3Cu4Sn4, Nd3Ag4Sn4, and Ho3Cu4Sn4 have been studied using 119Sn Mössbauer spectroscopy. Contrary to recent neutron diffraction data, Nd3Cu4Sn4 shows a clear magnetic signal at 1.6 K and has an ordering temperature of 2.0(1) K. Nd3Ag4Sn4 orders at 4.8(1) K, in agreement with neutron diffraction measurements. We observe the ordering of the Ho 2d sublattice in Ho3Cu4Sn4 at 8.2(1) K but we also see some residual magnetic splitting up to 10.5(2) K, which was not previously detected by neutron scattering. [ABSTRACT FROM AUTHOR]

Nd3Cu4Sn4, Nd3Ag4Sn4, and Ho3Cu4Sn4 have been studied using 119Sn Mössbauer spectroscopy. Contrary to recent neutron diffraction data, Nd3Cu4Sn4 shows a clear magnetic signal at 1.6 K and has an ordering temperature of 2.0(1) K. Nd3Ag4Sn4 orders at 4.8(1) K, in agreement with neutron diffraction measurements. We observe the ordering of the Ho 2d sublattice in Ho3Cu4Sn4 at 8.2(1) K but we also see some residual magnetic splitting up to 10.5(2) K, which was not previously detected by neutron scattering. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of Ln2CoGe4O12 (Ln = Gd, Tb, Dy, Ho or Er) and LnBCoGe4O12 (B = Sc or Lu) have been prepared and characterised by a combination of magnetometry, 155Gd Mössbauer spectroscopy and, in the case of Tb2CoGe4O12 and TbScCoGe4O12, neutron diffraction. The holmium- and erbium-containing compositions remain paramagnetic down to 2 K, those containing dysprosium behave as spin glasses and the terbium and gadolinium-containing compounds show long-range magnetic order with transition temperatures below 4 K in all cases. The data can be rationalized qualitatively in terms of the interplay between magnetic anisotropy and crystal field effects. [ABSTRACT FROM AUTHOR]

As part of our ongoing study of giant magnetocaloric compounds, we have determined the magnetic structure of Er5Si4 by high-resolution neutron powder diffraction, ac-susceptibility, and 166Er Mössbauer spectroscopy. The crystal space group is orthorhombic Pnma and the magnetic space group is Pn′ma′. The magnetic ordering temperature is 32(3) K and the magnetic structure is characterized by ferromagnetic order of the three Er sites (4c, 8d1, and 8d2) along [010], together with antiferromagnetic order of the 8d sites in the perpendicular (010) plane. The Er 4c magnetic mode is FY and the 8d magnetic mode is CX+FY+GZ+. At 3.6 K, the Er magnetic moments are 7.4(1), 6.9(2), and 7.6(2) μB at the 4c, 8d1, and 8d2 sites, respectively, and the corresponding 166Er hyperfine magnetic fields, at 5 K, are 715(5), 627(2), and 736(3) T. The neutron diffraction data show tentative evidence of a reorientation of the magnetic structure, most likely involving the development of an antiferromagnetic component at the 4c site, between 14 and 4 K. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

As part of our ongoing study of giant magnetocaloric compounds, we have determined the magnetic structure of Er5Si4 by high-resolution neutron powder diffraction, ac-susceptibility, and 166Er Mössbauer spectroscopy. The crystal space group is orthorhombic Pnma and the magnetic space group is Pn′ma′. The magnetic ordering temperature is 32(3) K and the magnetic structure is characterized by ferromagnetic order of the three Er sites (4c, 8d1, and 8d2) along [010], together with antiferromagnetic order of the 8d sites in the perpendicular (010) plane. The Er 4c magnetic mode is FY and the 8d magnetic mode is CX+FY+GZ+. At 3.6 K, the Er magnetic moments are 7.4(1), 6.9(2), and 7.6(2) μB at the 4c, 8d1, and 8d2 sites, respectively, and the corresponding 166Er hyperfine magnetic fields, at 5 K, are 715(5), 627(2), and 736(3) T. The neutron diffraction data show tentative evidence of a reorientation of the magnetic structure, most likely involving the development of an antiferromagnetic component at the 4c site, between 14 and 4 K. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have used neutron powder diffraction to demonstrate the existence of long-range antiferromagnetic order of Ising-like Dy moments in the DyCd6 quasicrystal approximant phase. This cubic compound undergoes a slight distortion to a monoclinic cell at low temperatures. The Néel temperature is 18.0(2) K and the magnetic order of the Dy sublattice may be described in the parent cubic I m 3 ¯ structure using a combination of two propagation vectors, k1 = [0 0 0] and k 2 = [ 1 2 0 1 2 ] , yielding 'anti-I' order. Alternatively, when referred to the monoclinic C2/c cell, the magnetic structure may be described by a single propagation vector: k = [1 0 0]. [ABSTRACT FROM AUTHOR]

We have used neutron powder diffraction to demonstrate the existence of long-range antiferromagnetic order of Ising-like Dy moments in the DyCd6 quasicrystal approximant phase. This cubic compound undergoes a slight distortion to a monoclinic cell at low temperatures. The Néel temperature is 18.0(2) K and the magnetic order of the Dy sublattice may be described in the parent cubic I m 3 ¯ structure using a combination of two propagation vectors, k1 = [0 0 0] and k 2 = [ 1 2 0 1 2 ] , yielding 'anti-I' order. Alternatively, when referred to the monoclinic C2/c cell, the magnetic structure may be described by a single propagation vector: k = [1 0 0]. [ABSTRACT FROM AUTHOR]

155Gd Mössbauer spectroscopy and neutron powder diffraction have been used to study magnetic ordering in Gd5Ir2Bi and Gd5Ir2Sb. Despite the hyperfine fields (Bhf) at the two Gd sites differing by more than a factor of two for both compounds, the moments derived from neutron diffraction are essentially equal in Gd5Ir2Bi. This implies an unusual departure from the commonly assumed scaling between BhfGd and μGd. Neutron powder diffraction shows that Gd5Ir2Bi is a c-axis ferromagnet at 3.6 K. We find no evidence for a FM→AF transition. [ABSTRACT FROM AUTHOR]

The magnetic ordering of nanocrystalline gadolinium (crystallite sizes of 21 nm and 38 nm) has been studied using neutron diffraction and compared with that of a reference (~ 1 μm) sample. In contrast with bulk gadolinium in which the moments order initially parallel to the c-axis and then cant by as much as 60° away from the c-axis below 250 K, before rotating back towards the c-axis on further cooling, both nanocrystalline samples order with their moments canted by about 50° from the c-axis, and this canting angle is largely temperature independent. [ABSTRACT FROM AUTHOR]

A neutron powder diffraction study of EuFe2P2 at a wavelength of 2.3672(1) Å shows that the 6.6(3) μB Eu2+ moments order ferromagnetically at TC=30(1) K and are canted at an angle of 17(3)° from the c axis. No evidence for the previously proposed antiferromagnetic or helimagnetic structures was found. The almost axial ferromagnetic structure of EuFe2P2 contrasts sharply with the planar antiferromagnetism seen in EuFe2As2 and many other europium-transition metal pnictides, suggesting a delicate interplay between the Eu 4f and transition metal 3d electrons. [ABSTRACT FROM AUTHOR]

The magnetic ordering of superconducting single crystals of K0.80Fe1.76Se2.00 has been studied between 10 and 550 K using 57Fe Mössbauer spectroscopy. Despite being superconducting below Tsc∼30 K, the iron sublattice in K0.80Fe1.76Se2.00 clearly exhibits magnetic order from well below Tsc to its Néel temperature of TN=532±2 K. The iron moments are ordered almost parallel to the crystal c axis. The order collapses rapidly above 500 K and the accompanying growth of a paramagnetic component suggests that the magnetic transition may be first order, which may explain the unusual temperature dependence reported in recent neutron diffraction studies. [ABSTRACT FROM AUTHOR]

We review the complementary roles that 119Sn Mössbauer spectroscopy and neutron diffraction are playing in developing a complete description of magnetic ordering in the R3 Cu4Sn4 and R3Ag4Sn4 intermetallic compound series. We show that the two techniques yield consistent pictures of the order, and in many cases both are essential to obtaining a complete description. The recent neutron diffraction work on Sm3Cu4Sn4, Sm3Ag4Sn4 and Gd3Ag4Sn4 is highlighted. [ABSTRACT FROM AUTHOR]

The increasing availability of ³He-based cryostats is making it possible to add sub-Kelvin capabilities to powder diffraction instruments. However, there are many problems associated with cooling powders below 1 K, and if great care is not taken, the sample temperature may be far higher than that reported by a thermometer attached to the sample holder. This contribution describes two practical and effective strategies for mounting powder samples that yield equilibration times of at most a few ten of minutes. [ABSTRACT FROM AUTHOR]

The extreme absorption cross section of natural gadolinium has so far precluded routine neutron diffraction work on its alloys and compounds. However, it is shown here that an easily constructed flat-plate sample holder with silicon single-crystal windows can be used to place a thin layer of material in a neutron beam and obtain Rietveld refinement quality diffraction data in a modest time. The flat-plate geometry uses a large area to compensate for the necessarily thin sample. Demonstration data are presented on two intermetallic compounds, Sm3Ag4Sn4 and Gd3Ag4Sn4, and it is shown that both structural and magnetic information can be derived from the diffraction patterns. By working at a wavelength of 2.37 A, it is possible to observe the low-Q diffraction peaks associated with magnetic ordering. This simple methodology should now enable routine measurements on even the most highly absorbing materials. [ABSTRACT FROM AUTHOR]

Neutron diffraction measurements on weakly scattering or highly absorbing samples may demand custom mounting solutions. Two low-background sample holders based on inexpensive single-crystal silicon are described. One uses a conventional cylindrical geometry and is optimized for weakly scattering materials, while the other has a large-area flat-plate geometry and is designed for use with highly absorbing samples. Both holders yield much lower backgrounds than more conventional null-matrix or null-scattering materials and are essentially free from interfering Bragg peaks. [ABSTRACT FROM AUTHOR]

The magnetic structure and ordering temperatures of three intermetallic compounds which crystallize in the tetragonal ThCr2Si2 structure, TbCr2Si2, HoCr2Si2 and ErCr2Si2, have been determined by neutron diffraction, differential scanning calorimetry and magnetization measurements. The Cr-sublattice orders anti-ferromagnetically with Néel temperatures of 758 K for TbCr2Si2, 718 K for HoCr2Si2 and 692 K for ErCr2Si2. Chromium atoms located at 4d crystallographic sites are aligned anti-parallel along the c-axis, with GZCr magnetic modes. In contrast with metallic bcc Cr, the refined room temperature value of the ordered Cr moment is anomalously large for all three compounds. No long range magnetic order of the R sublattice in TbCr2Si2 and HoCr2Si2 is observed, whilst the Er sublattice in ErCr2Si2 orders independently of the Cr sublattice below 2.4 K with moments ferromagnetically aligned in the basal plane. [ABSTRACT FROM AUTHOR]

The magnetic structure of the TiNiSi-type GdNiSn compound has been studied by both 155Gd Mössbauer spectrocopy and neutron powder diffraction. The results suggest a square-wave modulated magnetic structure characterized by the propagation vector k = [0.426, 0.351, 0] and Gd magnetic moments of 6.52(15)μB (at 3.6 K) oriented along the c-axis. The results are compared with those of the isotypic RNiSn compounds and with the possible magnetic structures of GdNiSn proposed from earlier 155Gd Mössbauer work. [ABSTRACT FROM AUTHOR]