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Hybrid organic–inorganic halides containing Bi and Sb generally exhibit higher stability and lower toxicity compared to Pb analogues. In this work, the synthesis, crystal and electronic structures and optical properties of a brand-new methylammonium bismuth iodide, (MA)4Bi6I22 (MA+ = CH3NH3+), are reported. Interestingly, we find that the presence of the HgI2 is necessary for the targeted preparation of (MA)4Bi6I22. (MA)4Bi6I22 contains isolated [Bi6I22]4− clusters made of six edge-sharing octahedral BiI6 units, which are separated by MA+ cations in its 0D crystal structure. A relatively low optical band gap of 1.9 eV was estimated for (MA)4Bi6I22 based on diffuse reflectance measurements. An intense photoluminescence peak emerges at 636 nm at low temperatures that supports the assigned band gap value. Electronic structure calculations show the presence of flat bands in the valence and conduction bands, consistent with the low-dimensional structure of (MA)4Bi6I22, and slightly indirect nature of the bandgap. Our findings suggest that the use of facilitator moieties such as HgI2 may provide a pathway to obtaining alternative methylammonium bismuth iodides to (MA)3Bi2I9.

Giant magnetostriction in insulating magnetic materials is highly required for applications but is rarely observed. Here we show that giant magnetostriction $(g1500\phantom{\rule{0.16em}{0ex}}\mathrm{ppm})$ can be achieved in an insulating transition metal oxide $\mathrm{CaBa}{\mathrm{Co}}_{4}{\mathrm{O}}_{7}$ where the ferrimagnetic ordering at ${T}_{\mathrm{C}}\ensuremath{\sim}62\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ is associated with a huge change in the lattice. Moreover, because this material is pyroelectric with a nonswitchable electric polarization ($P$), the giant magnetostriction results in a pronounced magnetoelectric effect---a huge change of electric polarization $(\mathrm{\ensuremath{\Delta}}P\ensuremath{\sim}1.6\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{C}/\mathrm{c}{\mathrm{m}}^{2})$ in response to the applied magnetic field up to 60 T. Geometric frustration as well as the orbital instability of ${\mathrm{Co}}^{2+}/{\mathrm{Co}}^{3+}$ ions is believed to play a crucial role in the giant magnetostriction. Our study provides insights on how to achieve both giant magnetostriction and pronounced magnetoelectric effect in insulating transition metal oxides.

International audience; We investigate giant magnetoelectric coupling at a Mn spin crossover in [MnL]BPh (L = (3,5-diBr-sal)323) with a field-induced permanent switching of the structural, electric, and magnetic properties. An applied magnetic field induces a first-order phase transition from a high spin/low spin (HS-LS) ordered phase to a HS-only phase at 87.5 K that remains after the field is removed. We observe this unusual effect for DC magnetic fields as low as 8.7 T. The spin-state switching driven by the magnetic field in the bistable molecular material is accompanied by a change in electric polarization amplitude and direction due to a symmetry-breaking phase transition between polar space groups. The magnetoelectric coupling occurs due to a γη coupling between the order parameter γ related to the spin-state bistability and the symmetry-breaking order parameter η responsible for the change of symmetry between polar structural phases. We also observe conductivity occurring during the spin crossover and evaluate the possibility that it results from conducting phase boundaries. We perform ab initio calculations to understand the origin of the electric polarization change as well as the conductivity during the spin crossover. Thus, we demonstrate a giant magnetoelectric effect with a field-induced electric polarization change that is 1/10 of the record for any material.

Ferrotoroidal order, which represents a spontaneous arrangement of toroidal moments, has recently been found in a few linear magnetoelectric materials. However, tuning toroidal moments in these materials is challenging. Here, we report switching between ferritoroidal and ferrotoroidal phases by a small magnetic field, in a chiral triangular-lattice magnet BaCoSiO4 with tri-spin vortices. Upon applying a magnetic field, we observe multi-stair metamagnetic transitions, characterized by equidistant steps in the net magnetic and toroidal moments. This highly unusual ferri-ferroic order appears to come as a result of an unusual hierarchy of frustrated isotropic exchange couplings revealed by first principle calculations, and the antisymmetric exchange interactions driven by the structural chirality. In contrast to the previously known toroidal materials identified via a linear magnetoelectric effect, BaCoSiO4 is a qualitatively new multiferroic with an unusual coupling between several different orders, and opens up new avenues for realizing easily tunable toroidal orders. Toroidal moments arise from vortex like spin arrangements. These moments can then interact, giving rise to ferri- or ferro-toroidal order, though controlling such order is difficult. Here, the authors demonstrate a ferri-toroidal state in BaCoSiO4, which under an applied magnetic field exhibits multiple toroidal and metamagnetic transitions.

Magnetic frustration can produce exotic spin configurations and dynamics. Here, the authors explore the seemingly simple competition between ferromagnetic nearest- and antiferromagnetic next-nearest neighbor interactions along Ising spin chains, as realized in the magnetoelectric compound Lu${}_{2}$CoMnO${}_{6}$. Commonly, this situation is described by the axial next-nearest-neighbor Ising model. For the first time, the authors measure and calculate its correlated magnetic dynamics, resulting from a characteristic fractal set of first-order phase boundaries. Experiments and Monte Carlo simulations reveal a dynamics slowdown while approaching the phase transition regime.

Complex high-precision mechanical devices can be fabricated using a three-dimensional printing technology with the help of computer-aided design. Using 3D stereolithography, we have constructed a cryogenic goniometer for measurements in pulsed magnetic fields of up to 100 T, at temperatures as low as 0.5 K. We review the properties of several materials tested in developing the goniometer and report on its design and performance. The goniometer allows samples to be rotated in situ to a precision of 0.2° so that the field can be applied at many different angles to the samples' symmetry directions. Following its success, we establish that 3D printing is now a viable technology for pulsed field and other cryogenic probes.

We bring together magnetization, infrared spectroscopy, and lattice dynamics calculations to uncover the magnetic field-temperature (B-T) phase diagrams and vibrational properties of the [(CH3)2NH2]M(HCOO)3 (M = Mn2+, Co2+, Ni2+) family of multiferroics. While the magnetically driven transition to the fully saturated state in [(CH3)2NH2]Mn(HCOO)3 takes place at 15.3 T, substitution with Ni or Co drives the critical fields up toward 100 T, an unexpectedly high energy scale for these compounds. Analysis of the infrared spectrum of the Mn and Ni compounds across TC reveals doublet splitting of the formate bending mode which functions as an order parameter of the ferroelectric transition. By contrast, [(CH3)2NH2]Co(HCOO)3 reveals a surprising framework rigidity across the order−disorder transition due to modest distortions around the Co2+ centers. The transition to the ferroelectric state is thus driven by the dimethylammonium cation freezing and the resulting hydrogen bonding. Under applied field, the Mn (an...

${\mathrm{Sm}\mathrm{B}}_{6}$ is a candidate topological Kondo insulator that displays surface conduction at low temperatures. Here, we perform torque magnetization measurements as a means to detect de Haas--van Alphen (dHvA) oscillations in ${\mathrm{SmB}}_{6}$ crystals grown by aluminum flux. We find that dHvA oscillations occur in single crystals containing embedded aluminum, originating from the flux used to synthesize ${\mathrm{SmB}}_{6}$. Measurements on a sample with multiple, unconnected aluminum inclusions show that aluminum crystallizes in a preferred orientation within the ${\mathrm{SmB}}_{6}$ cubic lattice. The presence of aluminum is confirmed through bulk susceptibility measurements, but does not show a signature in transport measurements. We discuss the ramifications of our results.

The field of double perovskites is now advancing to three magnetic elements on the A, B and ${\mathrm{B}}^{\ensuremath{'}}$ sites. A series of iridium-based double perovskite compounds, $L{n}_{2}{\mathrm{CoIrO}}_{6}$ $(Ln=\mathrm{Eu}, \mathrm{Tb}, \mathrm{Ho})$, with three magnetic elements was synthesized as polycrystalline samples. The compounds crystalize in monoclinic structures with the space group $P{2}_{1}/n$. Magnetic properties of these hetero-tri-spin $3d\text{\ensuremath{-}}5d\text{\ensuremath{-}}4f$ systems were studied by magnetic susceptibility and field dependent magnetization in both DC and pulsed magnetic fields. All these compounds show ferrimagnetic transitions at temperatures ${T}_{C}$ above 100 K, which are attributable to antiferromagnetic coupling between ${\mathrm{Co}}^{2+}$ and ${\mathrm{Ir}}^{4+}$ spins. For ${\mathrm{Eu}}_{2}{\mathrm{CoIrO}}_{6}$, the magnetic properties are similar to those of ${\mathrm{La}}_{2}{\mathrm{CoIrO}}_{6}$. The ${\mathrm{Eu}}^{3+}$ spins show Van Vleck paramagnetism, and do not significantly interact with transition-metal cations. In contrast, ${\mathrm{Tb}}_{2}{\mathrm{CoIrO}}_{6}$ and ${\mathrm{Ho}}_{2}{\mathrm{CoIrO}}_{6}$ reveal a second transition to antiferromagnetic order below a lower temperature ${T}_{N}$. The temperature-induced ferrimagnetic-to-antiferromagnetic phase transition might be explained by a spin-reorientation transition. Moreover, a magnetic-field-induced spin-flop-like transition with a small hysteresis was observed below ${T}_{N}$ in these two compounds. The magnetic moments of all three compounds do not saturate up to 60 T at low temperatures. A moderate magnetocaloric effect was also observed in all three compounds. Our results should motivate further investigation of the spin configuration on single crystals of these iridium-based double perovskites.

A thermoreflectance method was used to measure intragranular thermal diffusivity and conductivity of samples having a composition of U-50 wt%Zr (U–50Zr). Three phases at this composition were investigated: the high temperature γ phase, the low temperature δ phase, and the metastable ω phase. This approach uses a tightly focused laser to inject micron scale thermal waves and a second tightly focused laser to monitor the temperature distribution. The thermal properties are extracted by comparing experimental temperature profiles to an analytical heat diffusion model. The probe laser can monitor the temperature field in orthogonal directions along the surface of the sample and is well suited to measure thermal anisotropy. We show that the δ phase exhibits significant thermal anisotropy. The γ phase has the highest thermal conductivity. The higher conductivity of the γ phase is thought to be due to the presence of Zr precipitates that slightly change the stoichiometry of the γ matrix. The highly disordered ω phase appears to be thermally isotropic and has a lower conductivity than the δ phase. Both observations are likely due to the presence of γ domains that reside between ω domains. This supposition is supported by the presence of thermal heterogeneities that appear as noise in the measured signals.

We present a high resolution method for measuring magnetostriction in millisecond pulsed magnetic fields at cryogenic temperatures with a sensitivity of $1.11\times10^{-11}/\sqrt{\rm Hz}$. The sample is bonded to a thin piezoelectric plate, such that when the sample's length changes, it strains the piezoelectric and induces a voltage change. This method is more sensitive than a fiber-Bragg grating method. It measures two axes simultaneously instead of one. The gauge is small and versatile, functioning in DC and millisecond pulsed magnetic fields. We demonstrate its use by measuring the magnetostriction of Ca$_3$Co$_{1.03}$Mn$_{0.97}$O$_6$ single crystals in pulsed magnetic fields. By comparing our data to new and previously published results from a fiber-Bragg grating magnetostriction setup, we confirm that this method detects magnetostriction effects. We also demonstrate the small size and versatility of this technique by measuring angle dependence with respect to the applied magnetic field in a rotator probe in 65 T millisecond pulsed magnetic fields.

We investigated the Josephson effect between the conventional superconductor Pb0.7In0.3 and Ba0.4K0.6 (FeAs)2 single crystals by performing directional point-contact experiments. The junctions were irradiated with microwaves and the behavior of the Shapiro steps as a function of the square root of the microwave power was studied by means of the RSJ model extended to the nonautonomous case with an rf current-source term. The analysis reveals that, for current injection along the ab plane, the current-phase relation deviates from being simply described by the standard sin(ϕ) (as we indeed observed along the c axis) and a dominant sin(2ϕ) component is observed. The results are compared with a theory of the dc Josephson effect, formulated by using a method based on the calculation of temperature Green’s function in the junction within the tight-binding model (Burmistrova et al., Phys. Rev. B 91, 214501, 2015). The comparison shows that the experimental results here presented strongly favor an s ±-wave symmetry of the order parameter in this compound.

We report a high-pressure $^{75}\mathrm{As}$ NMR study on the heavily hole-doped iron pnictide superconductor ${\mathrm{KFe}}_{2}{\mathrm{As}}_{2}$ (${T}_{c}\ensuremath{\approx}3.8$ K). The low-energy spin fluctuations are found to decrease with applied pressure up to 2 GPa, but then to increase again, changing in lockstep with the pressure-induced evolution of ${T}_{c}$. Their diverging nature suggests close proximity to a magnetic quantum critical point at a negative pressure of $P\ensuremath{\simeq}\ensuremath{-}0.6$ GPa. Above 2.2 GPa, the $^{75}\mathrm{As}$ satellite spectra split below 40 K, indicating a breaking of As site symmetry and an incipient charge order. These pressure-controlled phenomena demonstrate the presence of nearly critical fluctuations in both spin and charge, providing essential input for the origin of superconductivity.

Domain wall motion is detected for the first time during the transition to a ferroelastic and spin state ordered phase of a spin crossover complex. Single‐crystal X‐ray diffraction and resonant ultrasound spectroscopy (RUS) revealed two distinct symmetry‐breaking phase transitions in the mononuclear Mn3+ compound [Mn(3,5‐diBr‐sal2(323))]BPh4, 1. The first at 250 K, involves the space group change Cc→Pc and is thermodynamically continuous, while the second, Pc→P1 at 85 K, is discontinuous and related to spin crossover and spin state ordering. Stress‐induced domain wall mobility was interpreted on the basis of a steep increase in acoustic loss immediately below the the Pc‐P1 transition, Stresses and strains: Domain wall motion is detected for the first time in a spin crossover crystal. Mobility of ferroelastic domain walls was interpreted on the basis of a steep increase in acoustic loss below a first order transition. Spin state ordering and domain formation is associated with collapse of the Jahn–Teller distortion on switching from the spin quintet to spin triplet form of a mononuclear Mn3+ complex.