Antiferromagnetic Reflections Research Articles

Magnetic and crystal structure of the antiferromagnetic skyrmion candidate GdSb0.71Te1.22

GdSb0.46Te1.48, a nonsymmorphic Dirac semimetal with Dirac nodes at the Fermi level, has a rich magnetic phase diagram with one of the phases predicted to be an antiferromagnetic skyrmion state. In the current work, we investigate GdSb0.71Te1.22 through bulk magnetization measurements, single-crystal, and powder synchrotron X-ray diffraction, as well as single-crystal hot-neutron diffraction. We resolve a weak orthorhombic distortion with respect to the tetragonal structure and charge density wave (CDW) satellites due to incommensurate modulations of the crystal structure. At 2 K the magnetic structure is modulated with two propagation vectors, kI = (0.45 0 0.45) and kII = (0.4 0 0), with all their arms visible. While kI persists up to the transition to the paramagnetic state at TN = 11.9 K, kII disappears above an intermediate magnetic transition at T1 = 5 K. Whereas magnetic field applied along the c-axis has only a weak effect on the intensity of antiferromagnetic reflections, it is effective in inducing an additional ferromagnetic component on Gd atoms. We refine possible magnetic structures of GdSb0.71Te1.22 and discuss the possibility of hosting magnetic textures with non-trivial 3D+ 2 topologies in the GdSb1−xTe1+x series.

Mn2VAl Heusler alloy thin films: appearance of antiferromagnetism and exchange bias in a layered structure with Fe

Mn2VAl Heusler alloy films were epitaxially grown on MgO(1 0 0) single-crystal substrates by ultra-high-vacuum magnetron sputtering. A2- and L21-type Mn2VAl order was controlled by the deposition temperature. A2-type Mn2VAl films showed no spontaneous magnetization, while L21-type Mn2VAl films showed ferrimagnetic behaviour with a maximum saturation magnetization of 220 emu cm−3 at room temperature (RT). An antiferromagnetic reflection was observed with neutron diffraction at RT for an A2-type Mn2VAl film deposited at 400 °C. A bilayer sample of the antiferromagnetic A2-type Mn2VAl and Fe showed an exchange bias of 120 Oe at 10 K.

The investigation of magnetic phase transition in cobaltite perovskites by high-resolution neutron powder diffraction under 14 T magnetic field

We carried out neutron powder diffraction (NPD) experiments on the layered perovskite cobaltite PrBaCo2O5.5+x (x = 0.24) at Super High Resolution Neutron Powder Diffractometer (SuperHRPD) with a newly installed magnet. At low temperatures, the antiferromagnetic (AFM) reflections of the NPD profile are suppressed whilst ferromagnetic (FM) reflections are enhanced under 14 T magnetic field. The magnetic-field-induced AFM-FM transition reveals the ground-state energy of FM is close to that of AFM.

Evidence for antiferromagnetic-type ordering off-electron multipoles inPrIr2Zn20

Neutron diffraction measurements conducted under applied magnetic fields evidence the ordered structure of ${\mathrm{PrIr}}_{2}{\mathrm{Zn}}_{20}$ below approximately 0.1 K. A two-channel (orbital) Kondo effect is expected to act within the non-Kramers doublet ground state of the Pr $4f$ electrons of this material in cubic symmetry. Antiferromagnetic reflections are clearly induced under the influence of applied magnetic fields, which are characterized by the propagation vector $\mathbit{q}=(1/2,1/2,1/2)$. This result indicates antiferromagnetic-type ordering of the Pr $f$-electron multipoles. The ${\mathrm{\ensuremath{\Gamma}}}_{3}$-type quadrupole, ${O}_{2}^{2}$, is the dominant order parameter deduced from the observed magnetic structure factor. We also discuss the entanglement of various finite-magnitude multipoles up to third rank, which are relevant to the low-energy crystalline-electric-field split levels in this material.

Field-induced magnetic states in holmium tetraboride

A study of the zero field and field induced magnetic states of the frustrated rare earth tetraboride, HoB$_4$, has been carried out using single crystal neutron diffraction complemented by magnetisation measurements. In zero field, HoB$_4$ shows magnetic phase transitions at $T_{\mathrm{N1}}$ = 7.1 K to an incommensurate state with a propagation vector ($\delta$, $\delta$, $\delta'$), where $\delta$ = 0.02 and $\delta'$ = 0.43 and at $T_{\mathrm{N2}}$ = 5.7 K to a non-collinear commensurate antiferromagnetic structure. Polarised neutron diffraction measurements in zero field have revealed that the incommensurate reflections, albeit much reduced in intensity, persist down to 1.5 K despite antiferromagnetic ordering at 5.7 K. At lower temperatures, application of a magnetic field along the $c$-axis initially re-establishes the incommensurate phase as the dominant magnetic state in a narrow field range, just prior to HoB$_4$ ordering with an up-up-down ferrimagnetic structure characterised by the $(h,k,\frac{1}{3})$-type reflections between 18 and 24 kOe. This field range is marked by the previously reported $M/M_{\mathrm{sat}}$= $\frac{1}{3}$ magnetisation plateau, which we also see in our magnetisation measurements. The region between 21 and 33 kOe is characterised by the increase in the intensity of the antiferromagnetic reflections, such as (100), the maximum of which coincides with the appearance of the narrow magnetisation plateau with $M/M_{\mathrm{sat}}\approx$ $\frac{3}{5}$. Further increase of the magnetic field results in the stabilisation of a polarised state above 33 kOe, while the incommensurate reflections are clearly present in all fields up to 59 kOe. We propose the $H-T$ phase diagram of HoB$_4$ for the $H \parallel c$ containing both stationary and transitionary magnetic phases which overlap and show significant history dependence.

Antiferromagnetism in NiO Observed by Transmission Electron Diffraction

Neutron diffraction has been used to investigate antiferromagnetism since 1949. Here, we show that antiferromagnetic reflections can also be seen in transmission electron diffraction patterns from NiO. The diffraction patterns taken here came from regions as small as 10.5nm, and such patterns could be used to form an image of the antiferromagnetic structure with a nanometer resolution.

Evolution of three-dimensional correlations during the photoinduced melting of antiferromagnetic order in La0.5Sr1.5MnO4

Using time-resolved resonant soft x-ray diffraction, we measure the evolution of the full three-dimensional scattering volume of the antiferromagnetic superlattice reflection in the single-layer manganite La${}_{0.5}$Sr${}_{1.5}$MnO${}_{4}$on femtosecond time scales following photoexcitation. We find that the in-plane correlations are unchanged as a metastable state is entered, however there are subtle changes in the $c$-axis correlations. We observe a transient shift of the scattering ellipsoid along ($00L$) at very short times, and at longer time scales the short-range $c$-axis correlations are more robust than they are in equilibrium. Such results are not obtainable with any other techniques and hint at previously unresolved processes in the dynamics of photomelting in strongly correlated systems.

Reply to “Comment on `Details of Sample Dependence and Transport Properties of URu2Si2”'

The comment from Butch et al. gives the view of physicists who have carefully studied the effects of hydrostatic pressure (P) conditions on a specific crystal. In our article, we do not discuss this problem but we concentrate on the single crystal properties. The main reason is that it is a delicate point as pressure experiments are usually conducted with a constant volume in a clamp cell. For example, the combined effects of the solidification of the pressure medium and even feedback at the phase transition [for example here, hidden order (HO)] when the material may expand or contract in different directions can cause a departure from ideal hydrostatic conditions. As an observed experimental rule, the best approach to hydrostaticity is given when the crystal size is small in compared with the volume of the pressure cell, a condition which is never realized in pressure inelastic neutron scattering experiments. A key point in a detailed study of the pressure conditions to succeed is to realize comparative measurements in the same pressure cell as used in neutron scattering, as well as in situ pressure measurements. Such condition was realized in neutron scattering experiments, where a strain gauge was glued on the crystal face to trace where macroscopic phase transition occurs, and even to estimate pressure inhomogeneity. The work presented in our article was realized to characterize the sample quality at most and to be able to select samples for quantum oscillation experiments (Shubnikov–de Haas (SdH) and de Haas–van Alphen effect) to precisely determine the feedback between HO and antiferromagnetic (AF) properties on the Fermi Surface. The residual resistivity ratio (RRR) for URu2Si2 is a simple and an effective criterion for selecting the best material to enhance the quantum oscillation signal, even if RRR is estimated from the value at 2K and validity of Matthiesen’s rule can be discussed. In our experience, for example, no SdH signal was detected for samples with low RRR of below 50. It should be noted that complementary information is given by specific heat measurement. Because of the large extinction observed in the neutron diffraction pattern of crystals, the determination of an absolute value of the extrinsic tiny sublattice magnetization via the intensity of ‘‘residual’’ AF reflections is a difficult and delicate task. Electron microscopy up to now has not been sensitive enough in the characterization of strongly correlated uranium intermetallic compounds, as shown by contradictory results on UPt3 for example. 7,8) As suggested in our paper, electronic correlation may generate a new type of extended defects. In the article by Butch et al., the neutron diffraction experiments were realized under isobar conditions where the pressure in the pressure cell was estimated from the pressure applied through a capillary. At least for us, it is not obvious whether the isobar conditions are realized on the crystal as no direct measurement of the pressure is achieved on the crystal’s location in the pressure cell at low temperatures. Furthermore, the resistivity measurement was realized independently in a classical piston cylinder cell in a commercial cryostat with a conventional medium of a 1 : 1 volume mixture of n-pentane/isoamyl alcohol. The interesting point is that the disappearance of HO and of superconductivity occurs at Px, as already obtained from ac susceptibility measurements. Our experimental observation of P measurements on different crystals indicates that the collapse of the SC transition never coincides with Px obtained through resistivity measurements and varies from crystal to crystal with no simple relation with the RRR value. This is quite different from the data obtained by Butch et al. which shows a coincidence with Px. Figure 1 shows the resistivity data of (a) the crystal examined by the Butch et al. and (b) a crystal with RRR 1⁄4 270. As can be seen, a nice anomaly at HO is detected in (a), but quite different behavior is detected between the single crystals (a) and (b) at low temperatures T < 10K. It must be noted that in our article the RRR domain near 30 is the range in which the power law dependence seems to reach a minimum, suggesting a correlation between the electronic mean free path and the 1 10 10

Structural and magnetic transitions inGd5SixGe4−x(0≤x≤0.9)from neutron powder diffraction

Gd5SixGe4�x 0x 0.9 has been studied using neutron powder diffraction at a wavelength of 2.3724 A. Antiferromagnetic ordering of the full 7 B Gd moments in the Pnma magnetic space group is seen for Gd5Ge4, with the moments predominantly parallel to the c axis, with a significant a-axis component at the Gd 8d2 site. The remarkably strong 010 antiferromagnetic reflection has been used to map out the structural and magnetic phase diagram for this system and show that the OII → OI structural transformation never proceeds to completion in zero field. The absence of scattering that could be attributed to long-range FM order in the OI modification suggests that an externally applied field may be needed to stabilize the ferromagnetic state.

Soft X-ray resonant scattering study of single-crystal LaSr2Mn2O7

Soft X-ray resonant scattering studies at the Mn $L_{\texttt{II, III}}$- and the La $M_{\texttt{IV, V}}$- edges of single-crystal LaSr$_2$Mn$_2$O$_7$ are reported. At low temperatures, below $T_\texttt{N} \approx 160$ K, energy scans with a fixed momentum transfer at the \emph{A}-type antiferromagnetic (0 0 1) reflection around the Mn $L_{\texttt{II, III}}$-edges with incident linear $\sigma$ and $\pi$ polarizations show strong resonant enhancements. The splitting of the energy spectra around the Mn $L_{\texttt{II, III}}$-edges may indicate the presence of a mixed valence state, e.g., Mn$^{3+}$/Mn$^{4+}$. The relative intensities of the resonance and the clear shoulder-feature as well as the strong incident $\sigma$ and $\pi$ polarization dependences strongly indicate its complex electronic origin. Unexpected enhancement of the charge Bragg (0 0 2) reflection at the La $M_{\texttt{IV, V}}$-edges with $\sigma$ polarization has been observed up to 300 K, with an anomaly appearing around the orbital-ordering transition temperature, $T_{\texttt{OO}} \approx 220$ K, suggesting a strong coupling (competition) between them.

Hard x-ray resonant scattering study of Ni81Fe19(111)/CoO(111) exchange biased bilayer

We have employed hard x-ray resonant magnetic scattering to study the bulk antiferromagnetic domain state of the archetypal epitaxial Ni81Fe19(111)/CoO(111) exchange biased bilayer (Ni81Fe19 = Permalloy = Py). Tuning the x-ray energy to the Co K-edge, we were able to detect the () antiferromagnetic magnetic Bragg reflection from a 2000 Å thick CoO film covered by a 120 Å Py layer and capped by 50 Å gold. The temperature dependence of the () Bragg intensity and the rocking-width agrees well with previous neutron diffraction data. The average lateral size of antiferromagnetic domains is about 40 nm close to TN = 291 K.

Field induced magnetic order in the frustrated magnet gadolinium gallium garnet

Gd3Ga5O12, (GGG), has an extraordinary magnetic phase diagram, where no long range order is found down to 25 mK despite ΘCW ≈2 K. However, long range order is induced by an applied field of around 1 T. Motivated by recent theoretical developments and the experimental results for a closely related hyperkagome system, we have performed neutron diffraction measurements on a single crystal sample of GGG in an applied magnetic field. The measurements reveal that the H - T phase diagram of GGG is much more complicated than previously assumed. The application of an external field at low T results in an intensity change for most of the magnetic peaks which can be divided into three distinct sets: ferromagnetic, commensurate antiferromagnetic, and incommensurate antiferromagnetic. The ferromagnetic peaks (e.g. (112), (440) and (220)) have intensities that increase with the field and saturate at high field. The antiferromagnetic reflections have intensities that grow in low fields, reach a maximum at an intermediate field (apart from the (002) peak which shows two local maxima) and then decrease and disappear above 2 T. These AFM peaks appear, disappear and reach maxima in different fields. We conclude that the competition between magnetic interactions and alternative ground states prevents GGG from ordering in zero field. It is, however, on the verge of ordering and an applied magnetic field can be used to crystallise ordered components. The range of ferromagnetic (FM) and antiferromagnetic (AFM) propagation vectors found reflects the complex frustration in GGG.

Magnetic Correlation in the Ordered Phase of CeOs4Sb12

We performed neutron diffraction and magnetization measurements to reveal the nature of phase transition of a Kondo semiconductor CeOs 4 Sb 12 . Weak antiferromagnetic (AFM) reflections characterized by a wave vector q = (1 0 0) were observed, and the ordered moment value is around 0.07µ B /Ce at zero magnetic field. The AFM structure is rapidly suppressed by magnetic field of 1 T, in contrast to the transition temperature suggested to be enhanced by magnetic field. Only ferromagnetic correlation is observed above 1 T. Such drastic variation of the magnetic correlation is closely connected into the transport properties; the AFM ordered phase below 1 T and the induced ferromagnetic state above 1 T correspond to the semiconducting and metallic states, respectively.

Crystallographic phase transition within the magnetically ordered state ofCe2Fe17

X-ray diffraction experiments were performed on polycrystalline and single-crystal specimens of Ce{sub 2}Fe{sub 17} at temperatures between 10 and 300 K. Below T{sub t}=118{+-}2 K, additional weak superstructure reflections were observed in the antiferromagnetically ordered state. The superstructure can be described by a doubling of the chemical unit cell along the c direction in hexagonal notation with the same space group R3m as the room-temperature structure. The additional antiferromagnetic satellite reflections observed in earlier neutron diffraction experiments can be conclusively related to the appearance of this superstructure.

Phase transition of geometrically frustratedTbNiAlin a magnetic field

The phase transitions of the geometrically frustrated antiferromagnet $\mathrm{TbNiAl}$ in a magnetic field are studied by means of neutron powder diffraction, ac susceptibility, and muon spin relaxation $(\ensuremath{\mu}\mathrm{SR})$ measurements. Neutron powder diffraction reveals that, in addition to antiferromagnetic order, ferromagnetic order is induced in a field as low as $B\ensuremath{\sim}0.02\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. At higher fields, ferromagnetic and antiferromagnetic order coexist in different domains in the sample, and the domain balance depends on both magnetic field and temperature. Antiferromagnetic Bragg reflections are observed below a N\'eel temperature of ${T}_{\mathrm{N}}=47\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ which is independent of the field. Ferromagnetic Bragg peaks are observed below a field-dependent Curie temperature which increases from ${T}_{\mathrm{C}}=52\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ at $B=0.2\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ to ${T}_{\mathrm{C}}=70\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ at $B=5\phantom{\rule{0.3em}{0ex}}\mathrm{T}$. Both phase transitions are concurrently observed in ac susceptibility and $\ensuremath{\mu}\mathrm{SR}$ measurements.

Structure and magnetic properties of R-P phase Sr3Mn2− xFexO7−δ (0.10 ≤x≤ 0.5)

Double layer R-P (Ruddlesden-Popper) manganate phases were stabilized in an air atmosphere by partial substitution of Mn by Fe. The crystal structures and magnetic structures of the R-P phase Sr 3 Mn 2-x Fe x O 7-δ (x = 0.1, 0.2, and 0.5) have been refined from the room temperature and low temperature neutron diffraction data. All of these samples adopt space group 14/mmm at room temperature. 10 K diffraction patterns showed antiferromagnetic ordering and magnetic superlattice reflection pattern that can be indexed on a 2a 0 x 2a 0 x c 0 supercell for x = 0.1 and x = 0.2 samples. The temperature dependence of the ZFC (zero field cooled) and FC (field cooled) molar magnetic susceptibility curve showed divergence for x = 0.5 samples which implies that this double R-P phase shows spin-glass transition.

Pressure–temperature phase diagram of the heavy-electron superconductor [formula omitted

The pressure–temperature phase diagram of the heavy-electron superconductor URu 2 Si 2 has been reinvestigated by AC-susceptibility and elastic neutron-scattering (NS) measurements performed on a small single-crystalline rod ( 2 mm in diameter, 6 mm in length) in a Cu–Be clamp-type high-pressure cell ( P < 1.1 GPa ) . At ambient pressure, this sample shows the weakest antiferromagnetic (AF) Bragg reflections reported so far, corresponding to the volume-averaged staggered moment of μ o ∼ 0.011 μ B / U . Under applied pressure, the AF scattering intensity exhibits a sharp increase at P ∼ 0.7 GPa at low temperatures. The saturation value of the AF scattering intensity above 0.7 GPa corresponds to μ o ∼ 0.41 μ B / U , which is in good agreement with that ( ∼ 0.39 μ B / U ) observed above 1.5 GPa in our previous NS measurements. The superconductivity is dramatically suppressed by the evolution of AF phase, indicating that the superconducting state coexists only with the hidden order phase. The presence of parasitic ferro- and/or antiferromagnetic phases with transition temperatures T 1 ⋆ = 120 ( 5 ) , T 2 ⋆ = 36 ( 3 ) and T 3 ⋆ = 16.5 ( 5 ) K and their relationship to the low- T ordered phases are also discussed.

Neutron scattering study of magnetic structure and metamagnetic transition between low- and high-moment states ofNpNiGa5

Systematic neutron scattering experiments have been carried out in order to reveal the magnetic properties of $\mathrm{Np}\mathrm{Ni}{\mathrm{Ga}}_{5}$. We have observed a ferromagnetic transition with the magnetic moment parallel to the tetragonal $c$ axis at ${T}_{\mathrm{C}}=30\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We have also observed antiferromagnetic reflections with the propagation vector $\mathbit{q}=(1∕2\phantom{\rule{0.3em}{0ex}}1∕2\phantom{\rule{0.3em}{0ex}}1∕2)$, coexisting with the ferromagnetic component below ${T}_{\mathrm{N}}=18\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The direction of the antiferromagnetic component is perpendicular to the $c$ axis, most likely ${\ensuremath{\mu}}^{\mathrm{AF}}\ensuremath{\Vert}⟨1\phantom{\rule{0.3em}{0ex}}1\phantom{\rule{0.3em}{0ex}}0⟩$. Spin-polarized neutron scattering experiments have revealed that only Np carries a magnetic moment. The polarization of Ni atom is less than $0.03\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}∕\mathrm{Ni}$, judging from our experimental accuracy. Thus, we conclude that the magnetic moments of Np atoms exhibit the simple ferromagnetic ordering, ${T}_{\mathrm{N}}&lt;T&lt;{T}_{\mathrm{C}}$, while a canted antiferromagnetic structure appears where $T&lt;{T}_{\mathrm{N}}$. A cant angle $\ensuremath{\theta}$ of $\ensuremath{\sim}90\ifmmode^\circ\else\textdegree\fi{}$ between two adjacent Np moments and a magnetic moment $\ensuremath{\mu}$ of $\ensuremath{\sim}0.8\phantom{\rule{0.3em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}∕\mathrm{Np}$ at $3\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ have been estimated. The temperature and the magnetic field dependences of these two components have also been quantitatively analyzed. (i) It is quite unusual that the Np total moment increases with the transition from the ferromagnetic to canted antiferromagnetic structure. (ii) The metamagnetic transition cannot be explained in terms of a simple spin-flip mechanism with competing interactions and anisotropy. (iii) Furthermore, an unusual reduction of the Np magnetic moment is accompanied with the metamagnetic transition. From these results, we concluded that a remarkable change in the $5f$ electronic state between the ferromagnetic low-moment state and the canted antiferromagnetic high-moment state takes place at ${T}_{\mathrm{N}}$ and metamagnetic transition.

Uniform magnetic excitations in NiO nanoparticles

A sample of isolated disc shaped NiO nanoparticles was studied at the RITA-II triple axis spectrometer at SINQ (PSI) using the newly implemented multi-analyser blade imaging mode. The particles were 13 nm in diameter and had a thickness of about 2.5 nm. A non-dispersive spin excitation was observed at the antiferromagnetic ( 1 2 1 2 1 2 ) reflection at a scattering vector of κ = 1.30 Å - 1 , at an energy of 0.51 ± 0.02 meV . This is shown to be due to uniform magnetic excitations in the nanoparticles.

Magnetic, specific heat and powder neutron diffraction studies of Ho [formula omitted]In

The successive magnetic transitions and magnetic structure of hexagonal Ho 2 In compound have been investigated by the magnetic, specific heat and powder X-ray and neutron diffraction measurements. Two magnetic phase transitions have been observed at the paramagnetic to ferromagnetic transition temperature T c = 85.0 ( 2 ) K and the magnetic order–order transition temperature T t = 32.5 ( 2 ) K. No antiferromagnetic reflections have been observed in the neutron diffraction patterns. The Rietveld analysis has indicated that the Ho atoms possess different moment values at two inequivalent sites: 8.8(2) μ B and 9.0(2) μ B at 2 K and 7.0(2) μ B and 7.4(2) μ B at 45 K, respectively. The moment direction from the hexagonal c -axis is 41 ( 10 ) ∘ at 2 K. At 45 K, the reliability factor takes so shallow minimum at around 26 ( 20 ) ∘ that one cannot exclude the alignment of moments along the c -axis in the higher temperature phase. A model is suggested for the magnetic structure change at T t .