Commensurate Magnetic Structure Research Articles

Understanding unconventional magnetic order in a candidate axion insulator by resonant elastic x-ray scattering

Magnetic topological insulators and semimetals are a class of crystalline solids whose properties are strongly influenced by the coupling between non-trivial electronic topology and magnetic spin configurations. Such materials can host exotic electromagnetic responses. Among these are topological insulators with certain types of antiferromagnetic order which are predicted to realize axion electrodynamics. Here we investigate the highly unusual helimagnetic phases recently reported in EuIn2As2, which has been identified as a candidate for an axion insulator. Using resonant elastic x-ray scattering we show that the two types of magnetic order observed in EuIn2As2 are spatially uniform phases with commensurate chiral magnetic structures, ruling out a possible phase-separation scenario, and we propose that entropy associated with low energy spin fluctuations plays a significant role in driving the phase transition between them. Our results establish that the magnetic order in EuIn2As2 satisfies the symmetry requirements for an axion insulator.

Pressure tuning of magnetic states in elemental thulium

The magnetic and structural properties of elemental thulium were studied by means of neutron powder diffraction at pressures up to 5.5 GPa in the temperature range 7 – 290 K. At ambient pressure below TN = 52 K, the incommensurate magnetic state with a longitudinal sinusoidal modulation and propagation vector q = (0, 0, qz) was formed. The qz value increases on cooling from 0.279(2) and reaches the commensurate value of 2/7 at the temperature T1 = 24 K. The new magnetic arrangement is of an antiphase domain structure, composed of structural blocks involving three or four hexagonal layers with magnetic moment directions parallel within a given block and oppositely alternating from block to block along the c axis. Under high pressure, the TN value increases slightly up to 57 K at 5.5 GPa with a pressure coefficient dTN/dP = 0.9 K/GPa. The pressure dependence of the T1 temperature is more pronounced with a pressure coefficient dT1/dP = 2.9 K/GPa. The arrangement of commensurate magnetic structures formed below T1 is strongly pressure dependent. A formation of the complex magnetic states composed of structural blocks involving three or four hexagonal layers with magnetic moment signs alternating from block to block along the c axis with qz = 7/23 at 2 GPa and qz = 7/22 at 5.5 GPa was observed. The lattice compression of Tm at T = 7 K demonstrates a weak anisotropy with the most compressible c axis.

Neutron diffraction and linear Grüneisen parameter studies of magnetism in NdFe2Ga8

We study the magnetism in ${\mathrm{NdFe}}_{2}{\mathrm{Ga}}_{8}$ by the neutron-diffraction and temperature-modulated linear Gr\"uneisen parameter measurements. Previous thermodynamical measurements have demonstrated that there are two magnetic transitions at 10 and 14.5 K, respectively. Neutron-diffraction measurements confirm that the lower one is an antiferromagnetic (AFM) transition with a commensurate magnetic structure. Both the commensurate and the incommensurate (IC) magnetic peaks are found below the higher transition but their intensities only gradually increase with decreasing temperature. Below 10 K, the commensurate peak intensity increases quickly with decreasing temperature, signaling the AFM transition, while the IC peak intensity disappears below 5 K. The linear Gr\"uneisen parameter along the $c$ axis, ${\mathrm{\ensuremath{\Gamma}}}_{c}$, shows a hysteresis behavior that is different from the hysteresis behavior for the magnetization $M$. We give a discussion of the origin of the magnetism in ${\mathrm{NdFe}}_{2}{\mathrm{Ga}}_{8}$.

Commensurate and incommensurate magnetic structure of the moderately frustrated antiferromagnet Li2M(WO4)2 with M=Co,Ni

We have investigated the magnetic structure of ${\mathrm{Li}}_{2}\mathrm{Co}{({\mathrm{WO}}_{4})}_{2}$ via magnetic susceptibility, and neutron diffraction measurements. Two magnetic transitions are observed in magnetic susceptibility at ${T}_{N1}\ensuremath{\sim}9.5\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${T}_{N2}\ensuremath{\sim}7.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Neutron diffraction reveals an incommensurate magnetic order with a wave vector ${k}_{\text{ICM}}=(\ensuremath{\sim}0.46,\ensuremath{\sim}0.27,\ensuremath{\sim}0.24$) between ${T}_{N1}$ and ${T}_{N2}$ and a commensurate magnetic order with a wave vector ${k}_{\text{CM}}=(0.5,0.25,0.25)$ below ${T}_{N2}$. The magnetic periodicity in the commensurate phase is four times larger than the nuclear unit cell length along the $b$- and $c$-axis directions with a saturated magnetic moment equal to $\ensuremath{\approx}2.92\phantom{\rule{4pt}{0ex}}{\ensuremath{\mu}}_{B}$. Below ${T}_{N1}$, the ICM wave vector for ${\mathrm{Li}}_{2}\mathrm{Co}{({\mathrm{WO}}_{4})}_{2}$ varies with decreasing temperature and locked into commensurate at ${T}_{N2}$, whereas weaker temperature dependence of ${k}_{\text{ICM}}=(0.46,0.17,0.33)$ is observed for ${\mathrm{Li}}_{2}\mathrm{Ni}{({\mathrm{WO}}_{4})}_{2}$.

Investigation of the magnetic ground state of GaV4S8 using powder neutron diffraction

The magnetic ground state of polycrystalline Néel skyrmion hosting material GaV4S8 has been investigated using ac susceptibility and powder neutron diffraction. In the absence of an applied magnetic field GaV4S8 undergoes a transition from a paramagnetic to a cycloidal state below 13 K and then to a ferromagnetic-like state below 6 K. With evidence from ac susceptibility and powder neutron diffraction, we have identified the commensurate magnetic structure at 1.5 K, with ordered magnetic moments of 0.23(2) μ B on the V1 sites and 0.22(1) μ B on the V2 sites. These moments have ferromagnetic-like alignment but with a 39(8)° canting of the magnetic moments on the V2 sites away from the V4 cluster. In the incommensurate magnetic phase that exists between 6 and 13 K, we provide a thorough and careful analysis of the cycloidal magnetic structure exhibited by this material using powder neutron diffraction.

Magnetic ground states of Ce3TiSb5, Pr3TiSb5 and Nd3TiSb5 determined by neutron powder diffraction and magnetic measurements

The R 3TiSb5 ternary compounds, with R a light rare earth (La to Sm) have been reported to crystallize with the anti-Hf5CuSn3-type hexagonal structure (Pearson’s symbol hP18; space-group P63/mcm, N. 193). An early article that reported possible superconductivity in some of these intermetallic phases (namely those with R = La, Ce, and Nd) caught our attention. In this work, we have now refined the crystal structure of the R 3TiSb5 compounds with R = Ce, Pr and Nd by Rietveld methods using high-resolution neutron powder diffraction data. The magnetic ground states of these intermetallics have been investigated by low-temperature magnetization and high-intensity neutron diffraction. We find two different magnetic transitions corresponding to two related magnetic structures at T N1 = 4.8 K (k 1 = [0, 1/2, 1/8]) and T N2 = 3.4 K (k 2 = [0, 0, 1/8]), respectively for Ce3TiSb5. However, the magnetic ordering appears to occur following a peculiar hysteresis: the k 2-type magnetic structure develops only after the k 1-type phase fraction has first slowly ordered with time and the size of the ordered Ce3+ magnetic moment has become large enough to induce the second magnetic transition. At T = 1.5 K the maximum amplitude of the Ce moment in the coexisting phases amounts to μ Ce = 2.15 μ B. For Nd3TiSb5 an antiferromagnetic ordering below T N = 5.2 K into a relatively simpler commensurate magnetic structure with a magnetic moment of μ Nd = 2.14(3) μ B and magnetic propagation vector of k = [0, 0, 0], was determined. No evidence of superconductivity has been found in Nd3TiSb5. Finally, Pr3TiSb5 does not show any ordering down to 1.5 K in neutron diffraction while an antiferromagnetic ground state is detected in magnetization measurements. There is no sign of magnetic contribution from Ti atoms found in any of the studied compounds.

Magnetic Neutron Diffraction of Quasi-Two-Dimensional Magnets

This study is devoted to magnetic neutron diffraction analysis (elastic neutron scattering yielding information about spin ordering in magnetic materials). Experimental approaches to magnetism are intensely developed mainly due to the discovery of new functional materials with unusual properties. Nevertheless, magnetic neutron diffraction analysis is a unique method, which makes it possible to directly determine magnetic structures (i.e., values and mutual orientations of magnetic moments and their orientations relative to the crystallographic axes). Neutron diffraction proved to be a good instrument for studying both simple commensurate magnetic structures in bulk samples and more complex noncollinear spiral magnets. Magnetic neutron diffraction is widely applied for studying magnetic structures in nanoscale multilayer film materials. However, bulk samples with a layered crystal structure, which can be considered as natural quasi-two-dimensional objects due to the weakness of interlayer couplings, are of greater interest for physics of low-dimensional magnetism. Our neutron diffraction studies on quasi-two-dimensional magnets, transition-metal oxides A3M2SbO6 (A = Li or Na, M = Co or Ni) and rare-earth intermetallic compounds La1–xTbx(Ni1–xMnx)2Si2, are briefly considered.

Neutron powder diffraction study of NaMn2O4 and Li0.92Mn2O4 : Insights on spin-charge-orbital ordering

The high-pressure synthesized quasi-one-dimensional compounds NaMn$_2$O$_4$ and Li$_{0.92}$Mn$_2$O$_4$ are both antiferromagnetic insulators, and here their atomic and magnetic structures were investigated using neutron powder diffraction. The present crystal structural analyses of NaMn2O4 reveal that Mn3+/Mn4+ charge-ordering state exist even at low temperature (down to 1.5 K). It is evident from one of the Mn sites shows a strongly distorted Mn3+ octahedra due to the Jahn-Teller effect. Above TN = 39 K, a two-dimensional short-range correlation is observed, as indicated by an asymmetric diffuse scattering. Below TN, two antiferromagnetic transitions are observed (i) a commensurate long-range Mn3+ spin ordering below 39 K, and (ii) an incommensurate Mn4+ spin ordering below 10 K. The commensurate magnetic structure (kC = 0.5, -0.5, 0.5) follows the magnetic anisotropy of the local easy axes of Mn3+, while the incommensurate one shows a spin-density-wave order with kIC = (0,0,0.216). For Li$_{0.92}$Mn$_2$O$_4$, on the other hand, absence of a long-range spin ordered state down to 1.5 K is confirmed.

Origin of negative magnetization phenomena in (Tm1−xMnx)MnO3 : A neutron diffraction study

$(\mathrm{T}{\mathrm{m}}_{1\ensuremath{-}x}\mathrm{M}{\mathrm{n}}_{x})\mathrm{Mn}{\mathrm{O}}_{3}$ solid solutions were synthesized at a high pressure of 6 GPa and a high temperature of about 1570--1670 K for 2 h for $x=0$, 0.1, 0.2, and 0.3. Magnetic, dielectric, and neutron diffraction measurements revealed that the introduction of magnetic ${\mathrm{Mn}}^{2+}$ cations into the A site leads to an incommensurate spin structure for $x=0.1$ and to a ferrimagnetic structure for $x\ensuremath{\ge}0.2$. Commensurate magnetic structures have a much larger correlation length $(\ensuremath{\sim}400\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ for $x=0,\ensuremath{\sim}600\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ for $x=0.3)$ than the incommensurate magnetic structure $(\ensuremath{\sim}12\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$ for $x=0.1)$. The presence of ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Mn}}^{2+}$ (with different sizes) at the A site causes significant microstrain effects along the $a$ direction which are absent for $x=0$ and get stronger with increasing $x$. Magnetic ordering occurs at the N\'eel temperature ${T}_{N}=37\phantom{\rule{0.28em}{0ex}}\mathrm{K}\phantom{\rule{4pt}{0ex}}(x=0.1)$ and at the ferrimagnetic Curie temperatures ${T}_{C}=75\phantom{\rule{0.28em}{0ex}}\mathrm{K}\phantom{\rule{4pt}{0ex}}(x=0.2)$ and ${T}_{C}=104\phantom{\rule{0.28em}{0ex}}\mathrm{K}\phantom{\rule{4pt}{0ex}}(x=0.3)$. Ordering of magnetic Mn moments triggers short-range order (for $x=0.1)$ and long-range order (for $x\ensuremath{\ge}0.2)$ of the ${\mathrm{Tm}}^{3+}$ cations at the same temperature---an unusual situation in perovskite materials with a simple ${\mathrm{GdFeO}}_{3}$-type $Pnma$ structure. For $x=0.1$, long-range IC magnetic order [with propagation vector $\mathbf{k}=({k}_{0},0,0)$ and ${k}_{0}\ensuremath{\approx}0.40]$ of ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ cations at the B site coexists with short-range order of ${\mathrm{Tm}}^{3+}$ and ${\mathrm{Mn}}^{2+}$ moments at the A site. Short-range order is induced at the N\'eel temperature ${T}_{N}=37\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, increases towards an additional specific heat anomaly at $T=4\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, and remains at lower temperature. The ferrimagnetic structure [with propagation vector $\mathbf{k}=(0,\phantom{\rule{0.28em}{0ex}}0,\phantom{\rule{0.28em}{0ex}}0)]$ consists of ferromagnetically ordered ${\mathrm{Mn}}^{3+}$ and ${\mathrm{Mn}}^{4+}$ cations at the B site which are coupled antiferromagnetically with ordered ${\mathrm{Mn}}^{2+}$ moments at the A site. ${\mathrm{Tm}}^{3+}$ moments adopt a zigzag magnetic structure which contains a macroscopic ferromagnetic moment that aligns with the direction of the ordered ${\mathrm{Mn}}^{2+}$ moments. Towards low temperature, the ordered ${\mathrm{Tm}}^{3+}$ moments strongly increase and overcome the saturated magnetic Mn moments at the B site, and this behavior results in the observation of magnetization reversal or negative magnetization phenomena with a compensation temperature of about 15 K at small magnetic fields in the $x=0.2$ and 0.3 samples. This is a classical mechanism of the magnetization reversal effects for ferrimagnets.

Origin of ferroelectricity in orthorhombic LuFeO3

We demonstrate that small but finite ferroelectric polarization ($\sim$0.01 $\mu$C/cm$^2$) emerges in orthorhombic LuFeO$_3$ ($Pnma$) at $T_N$ ($\sim$600 K) because of commensurate (k = 0) and collinear magnetic structure. The synchrotron x-ray and neutron diffraction data suggest that the polarization could originate from enhanced bond covalency together with subtle contribution from lattice. The theoretical calculations indicate enhancement of bond covalency as well as the possibility of structural transition to the polar $Pna2_1$ phase below $T_N$. The $Pna2_1$ phase, in fact, is found to be energetically favorable below $T_N$ in orthorhombic LuFeO$_3$ ($albeit$ with very small energy difference) than in isostructural and nonferroelectric LaFeO$_3$ or NdFeO$_3$. Application of electric field induces finite piezostriction in LuFeO$_3$ via electrostriction resulting in clear domain contrast images in piezoresponse force microscopy.

Magnetic properties and magnetic structures of Nd2TGe6 (T = Ni, Cu)

ABSTRACTThe magnetic properties and magnetic structures of Nd2TGe6 (T = Ni and Cu) were studied by magnetometric and neutron diffraction measurements. Both compounds have an orthorhombic crystal structure of the Ce2CuGe6-type and are antiferromagnetic with the Néel temperatures of 6.4 K (Nd2NiGe6) and 9.8 K (Nd2CuGe6). Based on the neutron diffraction data the magnetic structures were determined. In the investigated compounds all magnetic moments are localized on the Nd atoms and form a collinear commensurate magnetic structure with the magnetic unit cell equal to the crystal one. The moments are parallel to the b-axis (T = Ni) or to the c-axis (T = Cu). The obtained magnetic structures are discussed on the basis of competition between the RKKY-type interactions and influence of Crystalline Electric Field (CEF).

Structural disorder and magnetic correlations driven by oxygen doping in Nd2NiO4+δ ( δ∼0.11 )

We investigated the influence of oxygen over-stoichiometry on apical oxygen disorder and magnetic correlations in Nd2NiO4+d (d~0.11) in the temperature range of 2-300 K by means of synchrotron x-ray powder diffraction, neutron single crystal and powder diffraction studies, combined with macroscopic magnetic measurements. In the investigated temperature range, the compound crystalizes in a tetragonal commensurate structure with the P42/ncm space group with excess oxygen atoms occupy the 4b (3/4 1/4 1/4) interstitial sites, coordinated by four apical oxygen atoms. Large and anisotropic thermal displacement parameters are found for equatorial and apical oxygen atoms, which are strongly reduced on an absolute scale compared to the Nd2NiO4.23 phase. Maximum Entropy analysis of the neutron single crystal diffraction data uncovered anharmonic contributions to the displacement parameters of the apical oxygen atoms, toward the nearest vacant 4b interstitial site, related to the phonon assisted oxygen diffusion mechanism. Macroscopic magnetization measurements and neutron powder diffraction studies reveal long-range antiferromagnetic ordering of the Ni-sublattice at TN ~ 53 K with a weak ferromagnetic component along the c-axis, while the long-range magnetic ordering of the Nd-sublattice occurs below 10 K. Temperature dependent neutron diffraction patterns show the appearance of a commensurate magnetic order at TN with the propagation vector k = (100) and the emergence of an additional incommensurate phase below 30 K, while both phases coexist at 2 K. The commensurate magnetic structure is best described by the P42/nc`m` Shubnikov space group. Refined magnetic moments of the Ni and Nd-sites at 2 K are 1.144(76) muB and 1.632(52) muB respectively. A possible origin of the incommensurate phase is discussed and a tentative magnetic phase diagram is proposed.

Debye temperature of single-crystal Cr with incommensurate and commensurate magnetic structure

Single crystals of Cr and Cr3%Mn doped with ∼0.2 at.% 119Sn were studied by means of 119Sn-site Mössbauer spectroscopy. Mössbauer spectra recorded in the temperature range of 78–300 K were analyzed using a hyperfine field distribution method. Additionally, the spectra recorded on the Cr3%Mn sample were analyzed in terms of three sextets. Derived therefrom values of a center shift, CS, were fitted to the Debye model yielded values of the Debye temperature, for Cr and for Cr3%Mn. The difference in the -value can be regarded as evidence that a spin-phonon coupling is different for the incommensurate and commensurate antiferromagnetic magnetic structure of chromium.

Magnetic properties and magnetic structures of R2TGe6 (T = Ni, Cu; R = Tb, Ho and Er)

The magnetic properties and magnetic structures of the R2TGe6 compounds (T = Ni and Cu, R = Tb, Ho and Er) were studied by magnetometric and neutron diffraction measurements. All compounds have an orthorhombic crystal structure of the Ce2CuGe6-type and are antiferromagnetic with the Néel temperatures ranging from 6 K for Er2CuGe6 up to 42 K for Tb2NiGe6. Based on the neutron diffraction data the magnetic structures were determined for R2NiGe6 (R = Tb, Er) and R2CuGe6 (R = Ho, Er). In these compounds the magnetic moments localized on the rare earth element form a collinear commensurate magnetic structure. The magnetic unit cell is equal to the crystal one in R2NiGe6 (R = Tb, Er) while it is doubled along the a-axis (propagation vector k = (½, 0, 0)) in R2CuGe6 (R = Ho and Er). The obtained magnetic structures are discussed on the basis of competition between the RKKY-type interactions and influence of Crystalline Electric Field (CEF).

Understanding the magnetism in noncentrosymmetric CeIrGe3 : Muon spin relaxation and neutron scattering studies

The magnetic properties of a pressure induced noncentrosymmetric heavy-fermion superconductor CeIrGe$_3$ have been investigated by muon spin relaxation ($\mu$SR), powder neutron diffraction (ND) and inelastic neutron scattering (INS) techniques at ambient pressure. For completeness we have also measured the ac magnetic susceptibility $\chi_{\rm ac}(T)$, dc magnetic susceptibility $\chi(T)$, dc isothermal magnetization $M(H)$ and heat capacity $C_{\rm p}(T,H)$ down to 2 K. CeIrGe$_{3}$ is known to exhibit pressure induced superconductivity ($T_{\rm c}\approx 1.5$ K) at a pressure of 20 GPa and antiferromagnetic ordering at 8.7 K, 4.7 K and 0.7 K at ambient pressure. Our $\chi_{\rm ac}(T)$ and $\chi(T)$ data show an additional anomaly near 6.2 K which is also captured in $C_{\rm p}(T)$ data. From $\chi_{\rm ac}(T)$, $\chi(T)$ and $C_{\rm p}(T)$ measurements we infer three antiferromagnetic transitions above 2 K at $T_{\rm N1}= 8.5$ K, $T_{\rm N2}= 6.0$ K and $T_{\rm N3}= 4.6$ K. Our $\mu$SR study also confirms the presence of three transitions through the observation of one frequency for $T_{\rm N2} < T\leq T_{\rm N1}$, two frequencies for $T_{\rm N3} < T\leq T_{\rm N2}$ and three frequencies for $T\leq T_{\rm N3}$ in the oscillatory asymmetry. The ND data reveal an incommensurate nature of the magnetic ordering at $T=7$ K with the propagation vector k = (0,0,0.688(3)), and a commensurate magnetic structure at $T=1.5$ K with the propagation vector locked to the value k = (0,0,2/3) and magnetic moments oriented along the $c$ axis. The commensurate structure couples a macroscopic ferromagnetic component, resulting in a strong dependence of the lock-in transition temperature on external magnetic field. The INS data show two well defined crystal electric field (CEF) excitations arising from the CEF-split Kramers doublet ground state of Ce$^{3+}$.

Magnetic order, hysteresis, and phase coexistence in magnetoelectric LiCoPO4

The magnetic phase diagram of magnetoelectric LiCoPO$_4$ is established using neutron diffraction and magnetometry in fields up to 25.9T applied along the crystallographic $b$-axis. For fields greater than 11.9T the magnetic unit cell triples in size with propagation vector Q = (0, 1/3, 0). A magnetized elliptic cycloid is formed with spins in the $(b,c)$-plane and the major axis oriented along $b$. Such a structure allows for the magnetoelectric effect with an electric polarization along $c$ induced by magnetic fields applied along $b$. Intriguingly, additional ordering vectors Q $\approx$ (0, 1/4, 0) and Q $\approx$ (0, 1/2, 0) appear for increasing fields in the hysteresis region below the transition field. Traces of this behavior are also observed in the magnetization. A simple model based on a mean-field approach is proposed to explain these additional ordering vectors. In the field interval 20.5-21.0T, the propagation vector Q = (0, 1/3, 0) remains but the spins orient differently compared to the cycloid phase. Above 21.0T and up until saturation a commensurate magnetic structure exists with a ferromagnetic component along $b$ and an antiferromagnetic component along $c$.

Complex magnetic incommensurability and electronic charge transfer through the ferroelectric transition in multiferroic Co3TeO6

Polarized and unpolarized neutron diffractions have been carried out to investigate the nature of the magnetic structures and transitions in monoclinic Co3TeO6. As the temperature is lowered below 26 K long range order develops, which is fully incommensurate (ICM) in all three crystallographic directions. Below 19.5 K additional commensurate magnetic peaks develop, consistent with the Γ4 irreducible representation, along with a splitting of the ICM peaks along the h direction which indicates that there are two separate sets of magnetic modulation vectors. Below 18 K, this small additional magnetic incommensurability disappears, ferroelectricity develops, an additional commensurate magnetic structure consistent with Γ3 irreducible representation appears, and the k component of the ICM wave vector disappears. Synchrotron x-ray diffraction measurements demonstrate that there is a significant shift of the electronic charge distribution from the Te ions at the crystallographic 8 f sites to the neighboring Co and O ions. These results, together with the unusually small electric polarization, its strong magnetic field dependence, and the negative thermal expansion in all three lattice parameters, suggest this material is an antiferroelectric. Below15 K the k component of the ICM structure reappears, along with second-order ICM Bragg peaks, which polarized neutron data demonstrate are magnetic in origin.

Non-collinear magnetic structure of manganese quadruple perovskite CdMn7O12

We report on the magnetic structure of CdMn7O12 determined by powder neutron diffraction. We were able to measure the magnetic structure of this Cd containing and highly neutron absorbing material by optimizing the sample geometry and by blending the CdMn7O12 with Aluminum powder. Below its Néel temperature TN1 all magnetic reflections can be indexed by a single commensurate propagation vector k = (0, 0, 1). This is different to the case of CaMn7O12 where the propagation vector is incommensurate and where an in-plane helical magnetic structure has been found. We observe a commensurate non-collinear magnetic structure in CdMn7O12 with in-plane aligned magnetic moments resembling the ones in CaMn7O12. However, the commensurate propagation vector prevents the appearance of a helical magnetic structure in CdMn7O12. Finally, we also observe a third structural phase transition below ~60 K that can be attributed to phase separation.

Determination of the magnetic structure of CePt2In7 by means of neutron diffraction

The magnetic structure of the heavy fermion antiferromagnet CePt$_2$In$_7$ is determined using neutron diffraction. We find a magnetic wave vector $\mathbf{q}_M = (1/2,1/2,1/2)$, which is temperature independent up to $T_N =$ 5.5 K. A staggered moment of 0.45(1)$\mu_B$ at 2 K resides on the Ce ion. The nearest-neighbor moments in the tetragonal basal plane are aligned antiferromagnetically. The moments rotate by 90$^\circ$ from one CeIn$_3$ plane to another along the $c$ axis. A much weaker satellite peak with an incommensurate magnetic wave vector $\mathbf{q}_M = (1/2,1/2,0.47)$ seems to develop at low temperature. However, the experimental data available so far are not sufficient to draw a definitive conclusion about the possible co-existence of commensurate and incommensurate magnetic structures in this material.

MAGNDATA: towards a database of magnetic structures. II. The incommensurate case

A free web page under the name MAGNDATA, which provides detailed quantitative information on more than 400 published magnetic structures, has been made available at the Bilbao Crystallographic Server (http://www.cryst.ehu.es). It includes both commensurate and incommensurate structures. In the first article in this series, the information available on commensurate magnetic structures was presented [Gallego, Perez-Mato, Elcoro, Tasci, Hanson, Momma, Aroyo &amp; Madariaga (2016). J. Appl. Cryst. 49, 1750–1776]. In this second article, the subset of the database devoted to incommensurate magnetic structures is discussed. These structures are described using magnetic superspace groups, i.e. a direct extension of the non-magnetic superspace groups, which is the standard approach in the description of aperiodic crystals. The use of magnetic superspace symmetry ensures a robust and unambiguous description of both atomic positions and magnetic moments within a common unique formalism. The point-group symmetry of each structure is derived from its magnetic superspace group, and any macroscopic tensor property of interest governed by this point-group symmetry can be retrieved through direct links to other programs of the Bilbao Crystallographic Server. The fact that incommensurate magnetic structures are often reported with ambiguous or incomplete information has made it impossible to include in this collection a good number of the published structures which were initially considered. However, as a proof of concept, the published data of about 30 structures have been re-interpreted and transformed, and together with ten structures where the superspace formalism was directly employed, they form this section of MAGNDATA. The relevant symmetry of most of the structures could be identified with an epikernel or isotropy subgroup of one irreducible representation of the space group of the parent phase, but in some cases several irreducible representations are active. Any entry of the collection can be visualized using the online tools available on the Bilbao server or can be retrieved as a magCIF file, a file format under development by the International Union of Crystallography. These CIF-like files are supported by visualization programs like Jmol and by analysis programs like JANA and ISODISTORT.