Short-range Antiferromagnetic Research Articles

Ambient pressure synthesis and structure and magnetic properties of a new A- and B-site ordered multinary quadruple perovskite.

Quadruple perovskites with high magnetic transition temperatures are an interesting class of compounds but are synthesized typically under high pressure. Ambient pressure synthesis of new multinary quadruple perovskites having a high global instability index (GII) and transition temperature can be interesting for future exploration of high-TC oxides. A new A- and B-site ordered multinary quadruple perovskite, LaCu3Fe2RuSbO12, is synthesized by conventional solid-state reactions at ambient pressure. Rietveld structure refinement revealed that the compound crystallizes in the Pn3̄ space group with a lattice parameter of 7.4556(4) Å. The compound showed complete 1 : 3 ordering of La and Cu at the A-site and 1 : 1 rock-salt ordering of Fe with Ru/Sb at the B-site. The compound is also probed with scanning and transmission electron microscopy and XPS to investigate the chemical composition, microstructure, lattice and oxidation states of the elements. Magnetic studies revealed antiferromagnetic (AFM) correlations with magnetic ordering transitions at ∼170 and 40 K. Furthermore, the M-H hysteretic behavior at 100 and 5 K indicated ferrimagnetism due to short-range AFM interactions among Fe3+(3d5) and Ru4+(4d4) spins involving Cu2+(↑)-Fe3+(↓)-Ru4+(↑) triads. The specific heat data reaffirmed the magnetic signatures while electrical transport showed semiconducting behavior with variable range hopping. The details of synthesis and structural and compositional studies along with the magnetic and electrical transport properties of LaCu3Fe2RuSbO12 are reported in this paper.

Ground state properties of the periodic Anderson model with electron–phonon interactions

The periodic Anderson model (PAM) is a fundamental model describing heavy fermion systems’ behavior. In this paper, we investigate the PAM in the presence of electron–phonon interactions. By utilizing a novel analytical methodology based on operator inequalities, we demonstrate that the ground state at half-filling is unique and in a spin-singlet state. Additionally, we establish that the ground state exhibits short-range antiferromagnetism.

Magnetic incommensurability, short-range correlations, and properties ofHo7Rh3

The crystal structure, thermal properties, and magnetic state of the rare-earth intermetallic compound ${\mathrm{Ho}}_{7}{\mathrm{Rh}}_{3}$ was studied using the measurements of the AC and DC magnetic susceptibility, magnetization, specific heat and thermal expansion, as well as by neutron and synchrotron powder diffraction. Below the N\'eel temperature ${T}_{\mathrm{N}}=32$ K, an incommensurate antiferromagnetic (AFM) structure of the spin density wave (SDW) type was observed, described by the magnetic superspace group $Cmc{2}_{1.}{1}^{\ensuremath{'}}(00g)0sss$ and the propagation vector ${\mathbf{k}}_{\mathrm{IC}}=(0\phantom{\rule{0.16em}{0ex}}0\phantom{\rule{0.16em}{0ex}}0.389)$. Further cooling leads to the spin reorientation transition and squaring-up transformation of the SDW magnetic structure below ${T}_{t1}=22$ K. The spin reorientation transition is accompanied by the emergence of a ferromagnetic component in the incommensurate magnetic structure upon cooling below ${T}_{t2}=9$ K. Using neutron diffraction, the existence of a short-range antiferromagnetic order was revealed up to temperatures twice as high as ${T}_{\mathrm{N}}$. These short-range AFM correlations were found to affect the magnetic susceptibility and thermal expansion, while the crystal structure retains its hexagonal symmetry below and above the N\'eel temperature.

Short-range antiferromagnetic interaction and spin-phonon coupling in La2CoMnO6 double perovskite

Weak antiferromagnetic (AFM) interaction in the ferromagnetic (FM) partially ordered La2CoMnO6 (LCMO) was detected by Raman spectroscopy by monitoring spin-phonon coupling. Because of the sensibility to probe short-range disorder and lattice modifications, the Raman spectroscopy showed to be an useful tool to indicate less remarkable magnetic transitions in LCMO compound. Apart from the expected spin-phonon coupling due to the long-range FM superexchange (Tc ∼230 K), phonons parameters pointed out an additional spin-phonon coupling related to the short-range AFM interaction at Tc ∼135 K, which was not detected from the magnetic bulk response. These results reinforce the Raman spectroscopy as a powerful technique to detect antisite disorder into A2B′B’’O6 magnetic double perovskites, whose magnetic properties are driven by superexchange interactions.

Antiferromagnetic short-range order and cluster spin-glass state in diluted spinel ZnTiCoO4

The nature of magnetism in the doubly-diluted spinel ZnTiCoO4 = (Zn2+) A [Ti4+Co2+] B O4 is reported here employing the temperature and magnetic field (H) dependence of dc susceptibility (χ), ac susceptibilities (χ′ and χ″), and heat capacity (C p) measurements. Whereas antiferromagnetic (AFM) Néel temperature T N = 13.9 K is determined from the peak in the ∂(χT)/∂T vs T plot, the fit of the relaxation time τ (determined from the peak in the χ″ vs T data at different frequencies) to the Power law: τ = τ 0 [(T − T SG)/T SG]−zν yields the spin glass freezing temperature T SG = 12.9 K, z ν ∼ 11.75, and τ 0 ∼ 10−12 s. Since the magnitudes of τ 0 and z ν depend on the magnitude of T SG, a procedure is developed to find the optimum value of T SG = 12.9 K. A similar procedure is used to determine the optimum T 0 = 10.9 K in the Vogel–Fulcher law: τ = τ 0 exp[E a/k B(T − T 0)] yielding E a/k B = 95 K, and τ 0 = 1.6 × 10−13 s. It is argued that the comparatively large magnitude of the Mydosh parameter Ω = 0.026 and k B T 0/E a = 0.115 (≪1) suggests cluster spin-glass state in ZnTiCoO4 below TSG. In the C p vs T data from 1.9 K to 50 K, only a broad peak near 20 K is observed. This and absence of λ-type anomaly near T N or T SG combined with the reduced value of change in magnetic entropy from 50 K to 1.9 K suggests only short-range AFM ordering in the system, consistent with spin-glass state. The field dependence of T SG shows slight departure (ϕ ∼ 4.0) from the non-mean-field Almeida–Thouless line T SG(H) = T SG(0) (1 − AH 2/ϕ ). Strong temperature dependence of magnetic viscosity S and coercivity H C without exchange bias, both tending to zero on approach to T SG from below, further support the spin-glass state which results from magnetic dilution driven by diamagnetic Zn2+ and Ti4+ ions leading to magnetic frustration. Magnetic phase diagram in the H–T plane is established using the high-field magnetization data M(H, T) for T < T N which reveals rapid decrease of T SG with increase in H whereas decrease in T N with increase in H is weaker, typical of AFM systems. For T > T N, the data of χ vs T are fit to the modified Curie–Weiss law, χ = χ 0 + C/(T + θ), with χ 0 = 3.2 × 10−4 emu mol−1 Oe−1 yielding θ = 4 K and C = 2.70 emu K mol−1 Oe−1. This magnitude of C yields effective magnetic moment = 4.65 μ B for Co2+, characteristic of Co2+ ions with some contribution from spin–orbit coupling. Molecular field theory with effective spin S = 3/2 of Co2+ is used to determine the nearest-neighbor exchange constant J 1/k B = 2.39 K AFM and next-nearest-neighbor exchange constant J 2/k B = −0.66 K (ferromagnetic).

Pressure-driven electronic and structural phase transition in intrinsic magnetic topological insulator MnSb2Te4

Intrinsic magnetic topological insulators provide an ideal platform to achieve various exciting physical phenomena. However, this kind of materials and related research are still very rare. In this work, we reported the electronic and structural phase transitions in the intrinsic magnetic topological insulator $\mathrm{Mn}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{4}$ driven by hydrostatic pressure. Electric transport results revealed that temperature dependent resistance showed a minimum value near short-range antiferromagnetic (AFM) ordering temperature ${{T}_{N}}^{\ensuremath{'}}$, which declines with pressure. The short-range AFM ordering was sensitive to pressure and fully suppressed above 11.5 GPa. The intensity of three Raman vibration modes in $\mathrm{Mn}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{4}$ declined quickly starting from 7.5 GPa and these modes become undetectable above 9 GPa, suggesting possible insulator-metal transition, which is further confirmed by theoretical calculation. In situ x-ray diffraction demonstrated that an extra diffraction peak appears near 9.1 GPa and $\mathrm{Mn}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{4}$ started to enter an amorphouslike state above 16.6 GPa, suggesting the structural origin of suppressed AFM ordering and metallization. This work has demonstrated the correlation among interlayer interaction, magnetic ordering, and electric behavior, which could be benefit the understanding of the fundamental properties of this kind of materials and devices.

Defect-induced ferromagnetism in a S\u2009=\u20091/2 quasi-one-dimensional Heisenberg antiferromagnetic chain compound

We present evidences that defects in the spin S = 1/2 Heisenberg antiferromagnetic chain (HAFC) compound can lead to ferromagnetism by studying the magnetic and thermal properties of the newly discovered quasi-one-dimensional (1D) metal–organic framework [CH3NH3][Cu(HCOO)3] (MACuF). Our findings suggest that the long-range ferromagnetic order at 3.7 K can be attributed to Cu2+ ions from the 2D networks constructed by the endpoints of the broken chains. In such a case, the intrinsic magnetism can emerge in this quasi-1D Heisenberg chain system at the background of the short-range antiferromagnetism. This unusual ferromagnetism found in HAFC not only enriches magnetic features in the low-dimensional systems, but helps to understand some of the exotic magnetic phenomena in other real quasi-1D magnetic materials.

Successive magnetic ordering in two CoII-ladder metal-organic frameworks

Metal-organic frameworks showing successive magnetic ordering are far less common than inorganic compounds. Here, we report two metal-organic frameworks [CoII(ox)(bphy)•0.1(DMF)•0.1(MeOH)] n ( 1 ) and [CoII3(ox)3(bphy)2(DMF)2] n ( 2 ) comprised of zigzag and necklace CoII-ladders, respectively. Together with a previously reported compound [CoII(ox)(bphy)•0.2(DMF)] n ( 3 ) consisting of spiraling zigzag CoII-ladders, these three compounds provide a good system for comparative structural and magnetic studies. Comprehensive magnetic analysis reveals that the three compounds undergo long-range magnetic ordering at ~2.6 K but exhibit vastly different short-range magnetic correlations: compound 1 shows short-range spin-canted antiferromagnetism ordering at ~14.0 K; compound 2 demonstrates successive short-range antiferromagnetism ordering at ~15.5 and ~12.6 K; compound 3 shows slow magnetic relaxation with T b≈ 4.6 K. These results demonstrate long-range magnetic ordering is readily accessible in the frameworks of ox2− bridging CoII-ladders linked by bphy, where short-range magnetic correlations can be systematicly tuned by the CoII-ladder structures.

Magnetic field dependence of the Schottky anomaly in filled skutterudites Pr1−xEuxPt4Ge12

By performing a series of thermodynamic measurements in an applied magnetic field $H_{\textrm{ext}}$, we investigated the effects of Eu substitution on the Pr sites in filled skutterudite compound Pr$_{1-x}$Eu$_x$Pt$_4$Ge$_{12}$ ($ 0 \leq x \leq 1$). A heat capacity Schottky anomaly is present over the whole doping range. For the samples with $x > 0.5$, these Schottky anomaly peaks shift to lower temperature with increasing $H_{\textrm{ext}}$. We argue that this behavior reflects the antiferromagnetic (AFM) ordering of the Eu moments, as the AFM transition is suppressed by $H_{\textrm{ext}}$. The Schottky peaks in the samples with $x \leq 0.5$ shift to higher temperatures with increasing magnetic field, signaling the presence of an internal magnetic field due to short-range AFM correlations induced by magnetic moments of neighboring Eu sites. In low $H_{\textrm{ext}}$, the Schottky gaps show a non-linear relationship with $H_{\textrm{ext}}$ as the magnetic moments become weakly magnetized. In high $H_{\textrm{ext}}$, the magnetic moments of Eu sites become completely aligned with $H_{\textrm{ext}}$. Thus, increasing $H_{\textrm{ext}}$ does not further increase the magnetization, hence the Schottky gaps increase linearly with $H_{\textrm{ext}}$

Atomic-scale fragmentation and collapse of antiferromagnetic order in a doped Mott insulator

Disentangling the relationship between the insulating state with a charge gap and the magnetic order in an antiferromagnetic (AF) Mott insulator remains difficult due to inherent phase separation as the Mott state is perturbed. Measuring magnetic and electronic properties at the atomic length scales would provide crucial insight, but this is yet to be experimentally achieved. Here we use spectroscopic-imaging spin-polarized scanning tunneling microscopy (SP-STM) to visualize periodic spin-resolved modulations originating from the AF order in a relativistic Mott insulator Sr2IrO4, and study these as a function of doping. We find that near insulator-to-metal transition (IMT), the long-range AF order melts into a fragmented state with short-range AF correlations. Crucially, we discover that the short-range AF order is locally uncorrelated with the observed spectral gap magnitude. This strongly suggests that short range AF correlations are unlikely to be the culprit behind inhomogeneous gap closing and the emergence of pseudogap regions near IMT. Our work establishes SP-STM as a powerful tool for revealing atomic-scale magnetic information in complex oxides.

Antiferromagnetic Semiconductor BaFMn0.5Te with Unique Mn Ordering and Red Photoluminescence.

Semiconductors possessing both magnetic and optoelectronic properties are rare and promise applications in opto-spintronics. Here we report the mixed-anion semiconductor BaFMn0.5Te with a band gap of 1.76 eV and a work function of 5.08 eV, harboring both antiferromagnetism (AFM) and strong red photoluminescence (PL). The synthesis of BaFMn0.5Te in quantitative yield was accomplished using the "panoramic synthesis" technique and synchrotron radiation to obtain the full reaction map, from which we determined that the compound forms upon heating at 850 °C via an intermediate unknown phase. The structure refinement required the use of a (3+1)-dimensional superspace group Cmme(α01/2)0ss. The material crystallizes into a ZrCuSiAs-like structure with alternating [BaF]+ and [Mn0.5Te]- layers and has a commensurately modulated structure with the q-vector of 1/6a* + 1/6b* + 1/2c* at room temperature arising from the unique ordering pattern of Mn2+ cations. Long-range AFM order emerges below 90 K, with two-dimensional short-range AFM correlations above the transition temperature. First-principles calculations indicate that BaFMn0.5Te is an indirect band gap semiconductor with the gap opening between Te 5p and Mn 3d orbitals, and the magnetic interactions between nearest-neighbor Mn2+ atoms are antiferromagnetic. Steady-state PL spectra show a broad strong emission centered at ∼700 nm, which we believe originates from the energy manifolds of the modulated Mn2+ sublattice and its defects. Time-resolved PL measurements reveal an increase in excited-state lifetimes with longer probe wavelengths, from 93 ns (at 650 nm) to 345 ns (at 800 nm), and a delayed growth (6.5 ± 0.3 ns) in the kinetics at 800 nm with a concomitant decay (4.1 ± 0.1 ns) at 675 nm. Together, these observations suggest that there are multiple emissive states, with higher energy states populating lower energy states by energy transfer.

Structure-property relationship in layered BaMn2Sb2 and Ba2Mn3Sb2O2

Layered transition-metal compounds have received great attention owing to their novel physical properties. Here, we present the structural, electronic, thermal, and magnetic properties of BaMn2Sb2 and Ba2Mn3Sb2O2 single crystals, both with the layered structure analogous to high-temperature superconductors. While the Mn moment in the MnSb4 tetrahedral environment forms G-type antiferromagnetic (AFM) ordering in both BaMn2Sb2 (TN1~443 K) and Ba2Mn3Sb2O2 (TN1~314 K), a short-range AFM order is found in the intercalated MnO2 layer at a much lower temperature (TN2~60 K) in Ba2Mn3Sb2O2. The directions of the ordered moments in these two magnetic sub-lattices of Ba2Mn3Sb2O2 are perpendicular to each other, even though the system is electrically conductive. This indicates that the large magnetic moments in these compounds are highly localized, leading to negligible coupling between MnSb4 and MnO2 layers in Ba2Mn3Sb2O2. These findings provide an insight into the structure-magnetism-based design principle for new superconductors.

Anomalous effects of Sc substitution and processing on magnetism and structure of (Gd1−xScx)5Ge4

Abstract The kinetic arrest observed in the parent Gd5Ge4 gradually vanishes when a small fraction (x = 0.025, 0.05 and 0.10) of Gd is replaced by Sc in (Gd1−xScx)5Ge4, and the magnetic ground state changes from antiferromagnetic (AFM) to ferromagnetic (FM). A first order phase transition coupled with the FM-AFM transition occurs at TC = 41 K for x = 0.05 and at TC = 53 K for x = 0.10 during heating in applied magnetic field of 1 kOe, and the thermal hysteresis is near 10 K. The first-order magnetic transition is coupled with the structural Sm5Ge4-type to Gd5Si4-type transformation. The magnetization measured as a function of applied magnetic field shows sharp metamagnetic-like behavior. At the same time, the AFM to paramagnetic transition in (Gd1−xScx)5Ge4 with x = 0.10, is uncharacteristically broad indicating development of strong short-range AFM correlations above the Neel temperature. Comparison of the magnetization data of bulk, powdered, and metal-varnish composite samples of (Gd0.95Sc0.05)5Ge4 shows that mechanical grinding and fabrication of a composite have little effect on the temperature of the first-order transformation, but short-range ordering and AFM/FM ratio below TC are surprisingly strongly affected.

Low‐Dimensional Magnetic Properties of Natural and Synthetic Mixite (Bi,Ca)Cu6(OH)6(AsO4)3·nH2O (n ≈ 3) and Goudeyite YCu6(OH)6(AsO4)3·nH2O (n ≈ 3)

The structural, vibrational, and especially the magnetic properties of natural and synthetic polycrystalline samples of the minerals mixite with composition (Bi,Ca)Cu6(OH)6(AsO4)3·nH2O (n ≈ 3) and goudeyite with composition YCu6(OH)6(AsO4)3·nH2O (n ≈ 3) were investigated. The magnetic susceptibilities are characterized by low‐dimensional antiferromagnetic short range ordering and can be well fitted by the theoretical susceptibilities of a spin S = 1/2 alternating Heisenberg chain with nearest‐neighbor spin exchange ranging between 200 K and 130 K for natural mixite and synthetic goudeyite, respectively. The alternation parameters, i.e. the ratios of nearest and next‐nearest neighbor spin exchange range between 0.52 for natural mixite and 0.75 for synthetic mixite and goudeyite, respectively. The experimentally observed spin exchange parameters are consistent with DFT calculations of the spin exchange parameters.

Evolution from Griffiths like phase to non-Griffiths like phase with Y doping in [formula omitted

Detailed analysis of the temperature dependent dc susceptibility data shows the modification from the Griffiths like phase (GP) to non-Griffiths like phase (non-GP) in (La1-xYx)0.7Ca0.3MnO3(x=0,0.3,0.4,0.5,0.6) compounds with x. The existence of non-Griffiths phase is revealed from the upward deviation of the inverse susceptibility (1/χ) versus temperature plot from the Curie-Weiss behavior for the compounds with x⩾0.5. Whereas Griffiths phase is identified from the downturn of 1/χ versus T plot from the Curie-Weiss line in the compounds with x=0.3,0.4. The increased lattice distortion (with x) decreases the M-O-Mn bond angle and at the same time increase the electron-phonon (e-ph) coupling which in turn decreases the ferromagnetic double exchange (DE) interactions and enhances the effective short-range antiferromagnetic superexchange interactions between Mn3+/Mn3+ and Mn4+/Mn4+ ions above the Curie temperature (TC). The enhancement of this short-range antiferromagnetic (SR-AFM) interactions have been attributed to the conversions from GP to non-GP phase. The increased SR-AFM interactions with Y doping has also been substantiated from the magnetocaloric study.

Relationship between Magnetic Anisotropy below Pseudogap Temperature and Short-Range Antiferromagnetic Order in High-Temperature Cuprate Superconductor

The central issue in high-temperature cuprate superconductors is the pseudogap state appearing below the pseudogap temperature $T^*$, which is well above the superconducting transition temperature. In this study, we theoretically investigate the rapid increase of the magnetic anisotropy below the pseudogap temperature detected by the recent torque-magnetometry measurements on YBa$_2$Cu$_3$O$_y$ [Y. Sato et al., Nat. Phys., 13, 1074 (2017)]. Applying the spin Green's function formalism including the Dzyaloshinskii--Moriya interaction arising from the buckling of the CuO$_2$ plane, we obtain results that are in good agreement with the experiment and find a scaling relationship. Our analysis suggests that the characteristic temperature associated with the magnetic anisotropy, which coincides with $T^*$, is not a phase transition temperature but a crossover temperature associated with the short-range antiferromagnetic order.

Enhanced moments of Eu in single crystals of the metallic helical antiferromagnetEuCo2−yAs2

The compound EuCo{2-y}As2 with the tetragonal ThCr2Si2 structure is known to contain Eu{+2} ions with spin S = 7/2 that order below a temperature TN = 47 K into an antiferromagnetic (AFM) proper helical structure with the ordered moments aligned in the tetragonal ab plane, perpendicular to the helix axis along the c axis, with no contribution from the Co atoms. Here we carry out a detailed investigation of the properties of single crystals. Enhanced ordered and effective moments of the Eu spins are found in most of our crystals. Electronic structure calculations indicate that the enhanced moments arise from polarization of the d bands, as occurs in ferromagnetic Gd metal. Electrical resistivity measurements indicate metallic behavior. The low-field in-plane magnetic susceptibilities chi{ab}(T < TN) for several crystals are reported that are fitted well by unified molecular field theory (MFT), and the Eu-Eu exchange interactions Jij are extracted from the fits. High-field magnetization M data for magnetic fields H||ab reveal what appears to be a first-order spin-flop transition followed at higher field by a second-order metamagnetic transition of unknown origin, and then by another second-order transition to the paramagnetic (PM) state. For H||c, the magnetization shows only a second-order transition from the canted AFM to the PM state, as expected. The critical fields for the AFM to PM transition are in approximate agreement with the predictions of MFT. Heat capacity Cp measurements in zero and high H are reported. Phase diagrams for H||c and H||ab versus T are constructed from the high-field M(H,T) and Cp(H,T) measurements. The magnetic part Cmag(T, H = 0) of Cp(T, H = 0) is extracted and is fitted rather well below TN by MFT, although dynamic short-range AFM order is apparent in Cmag(T) up to about 70 K, where the molar entropy attains its high-T limit of R ln8.

Antiferromagnetism in semiconductingSrMn2Sb2andBaMn2Sb2single crystals

Crystals of ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ and ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$ were grown using Sn flux and characterized by powder and single-crystal x-ray diffraction, respectively, and by single-crystal electrical resistivity $\ensuremath{\rho}$, heat capacity ${C}_{\mathrm{p}}$, and magnetic susceptibility $\ensuremath{\chi}$ measurements versus temperature $T$, and magnetization versus field $M(H)$ isotherm measurements. ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ adopts the trigonal ${\mathrm{CaAl}}_{2}{\mathrm{Si}}_{2}$-type structure, whereas ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$ crystallizes in the tetragonal ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$-type structure. The $\ensuremath{\rho}(T)$ data indicate semiconducting behaviors for both compounds with activation energies of $\ensuremath{\gtrsim}0.35$ eV for ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ and 0.16 eV for ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$. The $\ensuremath{\chi}(T)$ and ${C}_{\mathrm{p}}(T)$ data reveal antiferromagnetic (AFM) ordering at ${T}_{\mathrm{N}}$ = 110 K for ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ and 450 K for ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$. The anisotropic $\ensuremath{\chi}(T\ensuremath{\le}{T}_{\mathrm{N}})$ data also show that the ordered moments in ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ are aligned in the hexagonal $ab$ plane, whereas the ordered moments in ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$ are aligned collinearly along the tetragonal $c$ axis. The $ab$-plane $M(H)$ data for ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ exhibit a continuous metamagnetic transition at low fields $0&lt;H\ensuremath{\lesssim}1$ T, whereas ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$ exhibits no metamagnetic transitions up to 5.5 T. The $\ensuremath{\chi}(T)$ and ${C}_{{}_{\mathrm{p}}}(T)$ data for both ${\mathrm{SrMn}}_{2}{\mathrm{Sb}}_{2}$ and ${\mathrm{BaMn}}_{2}{\mathrm{Sb}}_{2}$ indicate strong dynamic short-range AFM correlations above their respective ${T}_{\mathrm{N}}$ up to at least 900 K within a local-moment picture, corresponding to quasi-two-dimensional magnetic behavior. The present results and a survey of the literature for Mn pnictides with the ${\mathrm{CaAl}}_{2}{\mathrm{Si}}_{2}$ and ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$ crystal structures show that the ${T}_{\mathrm{N}}$ values for the ${\mathrm{CaAl}}_{2}{\mathrm{Si}}_{2}$-type compounds are much smaller than those for the ${\mathrm{ThCr}}_{2}{\mathrm{Si}}_{2}$-type materials.

Evolution of Hall resistivity and spectral function with doping in the SU(2) theory of cuprates

Recent transport experiments in the cuprate superconductors linked the opening of the pseudogap to a change in electronic dispersion [S. Badoux et al., Nature 531, 210 (2015)]. Transport measurements showed that the carrier density sharply changes from $x$ to $1+x$ at the pseudogap critical doping, in accordance with the change from Fermi arcs at low doping to a large hole Fermi surface at high doping. The SU(2) theory of cuprates shows that antiferromagnetic short range interactions cause the arising of both charge and superconducting orders, which are related by an SU(2) symmetry. The fluctuations associated with this symmetry form a pseudogap phase. Here we derive the renormalised electronic propagator under the SU(2) dome, and calculate the spectral functions and transport quantities of the renormalised bands. We show that their evolution with doping matches both spectral and transport measurements.

Ultrasound propagation in bond frustrated HgCr2S4 spinel in magnetic fields

Ultrasound and magnetization studies of bond frustrated spinel HgCr2S4 are performed as a function of temperature in static magnetic fields. Beside the anharmonic effect, the sound velocity shows pronounced anomaly at the antiferromagnetic (AFM) transition at TN = 23 K with an additional significant increase of the order of 0.5% indicating a strong spin-lattice coupling. External magnetic fields enhance the ferromagnetic (FM) correlations and shift the anomalies to lower temperatures concomitantly with the reduction of the Néel temperature. The constructed H–T phase diagram beside the long-range AFM states reveals the state with induced FM order and regimes with short-range AFM and FM correlations as well.