Antiferromagnetic Transition Temperature Research Articles

Evidence of Long-Range and Short-Range Magnetic Ordering in the Honeycomb Na3Mn2SbO6 Oxide

We present a comprehensive study of the synthesis, structure, and magnetic properties of the honeycomb oxide Na3Mn2SbO6 supported by neutron diffraction, heat capacity, and magnetization measurements. The refinements of the neutron diffraction patterns (150, 50, and 45 K) using the Rietveld method confirm the monoclinic (S. G. C2/m) structure. Temperature-dependent magnetic susceptibilities measured at varying fields along with the heat capacity measurements demonstrate the coexistence of long-range ordering (∼42 K) and short-range ordering (∼65 K). The field-dependent isothermal magnetization measurements at 5 K indicate a spin-flop transition around 5 T. Rietveld refinements of the low-temperature (below 45 K) neutron diffraction data further confirm the long-range magnetic ordering. In addition, the temperature variation of the lattice parameters obtained from the neutron powder diffraction analysis exhibited a distinct anomaly near the antiferromagnetic transition temperature. The appearance of the concomitant broadened backgrounds in the neutron powder diffraction data collected at 80, 50, and 45 K supports the short-range ordering. The resultant magnetic structure consists of spins that are aligned antiparallel with the nearest neighbors and also with the spins of the adjacent honeycomb layers. The occurrence of a fully ordered magnetic ground state (Neel antiferromagnetic (AFM)) in Na3Mn2SbO6 consolidates the significance of fabricating new honeycomb oxides.

Observation of Electronic Structure Modification in the Hidden Order Phase of CeCoSi

CeCoSi with no local inversion symmetric crystal structure (P4/nmm) exhibits a phase transition of unknown origin (Hidden Order: HO) at about 12 K (T0) above the antiferromagnetic transition temperature (TN = 9.4 K). The electronic structure change across T0 was investigated with high-precision optical reflection spectroscopy. The optical spectrum changed from a typical metallic behavior above T0 to a gap-like structure at around 15 meV below T0. The gap-like structure was unchanged across TN except for the narrowing of the Drude component of carriers due to the suppression of magnetic fluctuations. This result suggests a slight change from the typical metallic electronic structure above T0 to that with an energy gap near the Fermi level in the HO phase. The change in electronic structure in the HO phase was concluded to be due to electron/valence instability.

Nonreciprocity of Optical Absorption in the Magnetoelectric Antiferromagnet CuB2O4

The change in the absorption spectra due to reversal of the direction of light propagation (nonreciprocity of absorption) is a consequence of a simultaneous violation of both time-reversal and spatial-inversion symmetries. Here, we report on a high-resolution spectroscopic study of absorption nonreciprocity in the noncentrosymmetric multiferroic CuB2O4 below the antiferromagnetic transition temperature TN = 21 K in the commensurate phase in magnetic fields up to 0.5 T. The study was performed in a broad spectral region covering several exciton transitions, which all are followed by an anomalously rich structure due to the multiple exciton-magnon-phonon satellites. Two components were resolved for the spectral line near 1.4 eV corresponding to the exciton transition between the ground and the first excited state. A quantitative theory of the optical absorption and nonreciprocity at this line was developed. The theory takes into account the interference between the electric and magnetic dipole contributions to the absorption and gives an adequate explanation of the relevant effects.

Electrical Interrogation of Thickness‐Dependent Multiferroic Phase Transitions in the 2D Antiferromagnetic Semiconductor NiI2

Abstract2D magnetic materials hold promise for quantum and spintronic applications. 2D antiferromagnetic materials are of particular interest due to their relative insensitivity to external magnetic fields and higher switching speeds compared to 2D ferromagnets. However, their lack of macroscopic magnetization impedes detection and control of antiferromagnetic order, thus motivating magneto‐electrical measurements for these purposes. Additionally, many 2D magnetic materials are ambient‐reactive and electrically insulating or highly resistive below their magnetic ordering temperatures, which imposes severe constraints on electronic device fabrication and characterization. Herein, these issues are overcome via a fabrication protocol that achieves electrically conductive devices from the ambient‐reactive 2D antiferromagnetic semiconductor NiI2. The resulting gate‐tunable transistors show band‐like electronic transport below the antiferromagnetic and multiferroic transition temperatures of NiI2, revealing a Hall mobility of 15 cm2 V−1 s−1 at 1.7 K. These devices also allow direct electrical probing of the thickness‐dependent multiferroic phase transition temperature of NiI2 from 59 K (bulk) to 28 K (monolayer).

Abnormal magnetic phenomenon at low temperature in Zn doped <inline-formula><tex-math id="M1">\begin{document}$ \left[{(\mathbf{C}\mathbf{H}}_{3}{)}_{2}\mathbf{N}{\mathbf{H}}_{2}\right]{\mathbf{C}\mathbf{o}}_{\mathit{x}}{\mathbf{Z}\mathbf{n}}_{1-\mathit{x}}{\left[\mathbf{H}\mathbf{C}\mathbf{O}\mathbf{O}\right]}_{3} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221761_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221761_M1.png"/></alternatives></inline-formula> frameworks

Metal-organic framework (MOF) is a new type of inorganic-organic hybrid porous material composed of organic ligands bridging metal ions, and it has the characteristics of tunable functions, good stability and porosity. In this study, Zn doped Co-based metal organic frame works single-crystal samples<inline-formula><tex-math id="M2">\begin{document}$\left[{(\rm{C}\rm{H}}_{3}{)}_{2}\rm{N}{\rm{H}}_{2}\right]{\rm{C}\rm{o}}_{1-x}{\rm{Z}\rm{n}}_{x} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221761_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221761_M2.png"/></alternatives></inline-formula><inline-formula><tex-math id="M2-1">\begin{document}$ {\left[\rm{H}\rm{C}\rm{O}\rm{O}\right]}_{3}$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221761_M2-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="3-20221761_M2-1.png"/></alternatives></inline-formula>are synthesized by the solvothermal method with normal ratio <i>x</i> = 0, 0.1, 0.2, 0.3, 0.4, 0.5. Single crystal diffraction, scanning electron microscope and energy dispersive X-ray spectroscopy results show that Zn ions are uniformly doped into Co-based MOFs crystals. The field cooling curves show that antiferromagnetic phase transition temperature of Co-based MOFs decreases from 15 K for pure Co-MOF <i>x</i> = 0 to 12.8 K for <i>x</i> = 0.2. Abnormal large magnetic hysteresis is obtained for Zn doped crystals with large coercive field 3600 Oe (<i>x</i> = 0.3) compared with 450 Oe coercive field for pure Co-MOF (<i>x</i> = 0), and the hysteresis area of Zinc-doped sample is more than 3 times that of pure cobalt sample. On the other hand, we find a series of steps on the hysteresis loop of DMCo<sub>0.9</sub>Zn<sub>0.1</sub>F sample, which gradually disappears with the increase of temperature, similar to the quantum tunneling phenomenon of a single molecule magnet. Previous studies have shown that the long range magnetic interaction and the magnetic single-ion behavior competition coexist in these systems. It is believed that the doping of non-magnetic zinc ions weakens the long-range interaction between Co ions and makes Co ions show the step effect caused by quantum tunneling at low temperature.

Effect of doping concentration on the antiferromagnetic transition temperature of multiferroic YMnO3: A first-principles study

Hexagonal YMnO3 is an attractive multiferroic material whose polarization and magnetic orders are strongly coupled with each other. Doping different cations in hexagonal YMnO3 would influence its properties, especially the magnetic transition temperature (the Néel temperature). In this work, by using first-principles calculations, we not only studied the effects of doping Fe and Cr ions at the Mn-site on the Néel temperature, but also revealed that the variations of electronic structures and the extents of orbital coupling overlaps are both factors to determine the magnetic interaction strength and Néel temperature for YMn1-x(Fe,Cr)xO3 (0 ≤ x < 0.3). Besides the Mn-site, doping rare earth element (La) at the non-magnetic Y-site also influences the Néel temperature. These results are important to provide more understanding about the performance of multiferroic materials.

An unusual magnetic phenomenon in Mg doping [(CH3)2NH2] CoxMg1−x[HCOO]3 frameworks

In this study, Mg doping metal-organic frameworks (MOFs) [(CH3)2NH2] Co1−x Mg x [HCOO]3 single crystals were synthesized by solvothermal method with normal ratios x = 0, 0.1, 0.2, 0.3, 0.4, 0.6. Powder X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDX) results showed that Mg ion is uniformly doped into Co-based MOFs crystal. With the increase of diamagnetic magnesium ions doping, the antiferromagnetic phase transition temperature of Co-based MOFs for pure Co-MOF decreased from 15 K to 7.5 K for x = 0.4. Abnormal larger magnetic hysteresis was obtained for Mg doping crystals with a large coercive field 3100 Oe (x = 0.1), 3700 Oe (x = 0.2), 2900 Oe (x = 0.3) compared with 600 Oe coercive field for pure Co-MOFs (x = 0). At the same time, step-like behavior was first observed on Mg2+ doping sample with x = 0.1–0.3. This unusual magnetic phenomenon is well interpreted based on the coexistence of long-range canted antiferromagnetic order and isolated single-ion quantum magnets. The diamagnetic magnesium ions doping decreases the strong exchange coupling between neighboring Co ions and step-like behavior stemmed from the quantum tunneling of isolated Co ions.

Effects of the on-site energy on the electronic response of Sr3(Ir1−xMnx)2O7

We investigated the doping and temperature evolutions of the optical response of Sr3(Ir1−xMnx)2O7 single crystals with 0 ≤ x ≤ 0.36 by utilizing infrared spectroscopy. Substitution of 3d transition metal Mn ions into Sr3Ir2O7 is expected to induce an insulator-to-metal transition via the decrease in the magnitude of the spin–orbit coupling and the hole doping. In sharp contrast, our data reveal the resilience of the spin–orbit coupling and the incoherent character of the charge transport. Upon Mn substitution, an incoherent in-gap excitation at about 0.25 eV appeared with the decrease in the strength of the optical transitions between the effective total angular momentum Jeff bands of the Ir ions. The resonance energies of the optical transitions between the Jeff bands which are directly proportional to the magnitude of the spin–orbit coupling hardly varied. In addition to these evolutions of the low-energy response, Mn substitution led to the emergence of a distinct high-energy optical excitation at about 1.2 eV which is larger than the resonance energies of the optical transitions between the Jeff bands. This observation indicates that the Mn 3d states are located away from the Ir 5d states in energy and that the large difference in the on-site energies of the transition metal ions is responsible for the incoherent charge transport and the robustness of the spin–orbit coupling. The effect of Mn substitution was also registered in the temperature dependence of the electronic response. The anomaly in the optical response of the parent compound observed at the antiferromagnetic transition temperature is notably suppressed in the Mn-doped compounds despite the persistence of the long-range antiferromagnetic ordering. The suppression of the spin-charge coupling could be related to charge disproportionation of the Ir ions.

Insights into the structural symmetry of YCrO3 from synchrotron X-ray diffraction

A high-resolution synchrotron X-ray diffraction study of a single-crystal YCrO3 compound was employed to obtain its crystallographic information, such as lattice parameters, atomic positions, bond lengths and angles, and local crystalline distortion size and mode. The measurements were taken at 120 K (below the antiferromagnetic transition temperature T N ≃ 141.5 K), 300 K (between T N and the ferroelectric transition temperature T C ≃ 473 K) and 500 K (above T C). Using the high intensity of synchrotron X-rays, it was possible to refine collected patterns with the previously proposed noncentrosymmetric monoclinic structural model (P1211, No. 4) and determine detailed structural parameters. Meanwhile, for a controlled study, the data were refined with the centrosymmetric orthorhombic space group (Pmnb, No. 62). The lattice constants a, b and c and the unit-cell volume increased nearly linearly upon heating. With the P1211 space group, the distributions of bond lengths and angles, as well as local distortion strengths, were observed to be more dispersed. This implies that (i) the local distortion mode of Cr2O6 at 120 K correlates with the formation of canted antiferromagnetic order by Cr1–Cr2 spin interactions, primarily via intermediate O3 and O4 ions; and (ii) the previously reported dielectric anomaly may have a microscopic origin in the strain-balanced Cr1—O3(O4) and Cr2—O5(O6) bonds as well as the local distortion modes of Cr1O6 and Cr2O6 octahedra at 300 K. Local crystalline distortion is shown to be an important factor in the formation of ferroelectric order. The comprehensive set of crystallographic information reported here allows for a complete understanding of the unique magnetic and ferroelectric properties of YCrO3.

First principles investigation of spin-orbit coupling driven magnetism of the 3d−5d double-perovskite (Sr/Ca)2FeIrO6

The interplay of spin-orbit coupling (SOC) with the other energy scales gives rise to various novel and interesting quantum phenomena in the Ir based double perovskites. In recent findings the double-perovskites ${\mathrm{Sr}}_{2}{\mathrm{FeIrO}}_{6}$ (SFIO) and ${\mathrm{Ca}}_{2}{\mathrm{FeIrO}}_{6}$ (CFIO) have been reported to fall under the category of a SOC driven antiferromagnetic (AFM) Mott insulator. Using density functional theory based first principles calculations, we have performed a comparative electronic structure investigation of these compounds. We reveal the microscopic origin of the difference in the AFM transition temperature observed in the experiments through the calculated exchange interactions and the Wannier functions. We addressed the role of SOC in dictating the ground state properties of these two compounds. Although both of the compounds are isoelectronic and isovalent, however, the effective strength and the impact of SOC is very different and nonmonotonic in these compounds, due to the delicate balance with the other energy scales. Our study advances the understanding of the nontrivial role of SOC in driving ground state magnetic properties of the Ir based oxides in general and explores the opportunities for further designing of the SOC driven quantum phases.

Unconventional magneto-transport properties of the layered antiferromagnet Fe1/3NbS2

Recently, magnetically intercalated layered transition metal dichalcogenide Fe1/3NbS2 has attracted considerable attention due to its promise for spintronics applications, especially for the demonstration of reversible resistance switching by electrical stimulation below the antiferromagnetic transition temperature. Magneto-transport properties and their correlation to the underlying magnetic configurations are yet to be clarified in Fe1/3NbS2. Herein, we investigate the magneto-transport behavior of antiferromagnet Fe1/3NbS2, demonstrating a complex behavior of the magnetoresistance and unconventional Hall effect. The resistance of this compound displayed metallic behavior and an abrupt decrease at TN. Of particular interest, the positive magnetoresistance is enhanced and it reaches a maximum in the vicinity of Néel temperature as a function of the out-of-plane magnetic field, which is in contrast to most of the antiferromagnets. Meanwhile, the Hall signal showed an unusual nonlinear field-dependence in the same temperature range. Moreover, the magnetoresistance exhibits a significant anisotropy, up to 14% near the Néel temperature. We attributed these unconventional magneto-transport behaviors to the field induced formation of a complex spin texture in Fe1/3NbS2. Our work motivates further efforts on antiferromagnetic spintronic devices based on this intercalated layered transition metal dichalcogenide.

Strain tuned magnetotransport of Jeff=1/2 antiferromagnetic Sr2IrO4 thin films

In this work, we report observation of strain effect on physical properties of Sr2IrO4 thin films grown on SrTiO3 (001) and LaAlO3 (001) substrates. It is found that the film on LaAlO3 with compressive strain has a lower antiferromagnetic transition temperature (TN~ 210 K) than the film on SrTiO3 (TN ~ 230 K) with tensile strain, which is probably caused by modified interlayer coupling. Interestingly, magnetoresistance due to pseudospin-flip of the film on LaAlO3 is much larger than that of tensile-strained film on SrTiO3, and robust anisotropic magnetoresistance is observed in the former, but H-driven reversal behavior is seen in the latter. By performing first principles calculations, it is revealed that epitaxial strain plays an efficient role in tuning the canting angle of Jeff = 1/2 moments and thus net moment at every IrO2 layer, responsible for the difference in magnetoresistance between the films. The reversal of anisotropic magnetoresistance of the thin film on SrTiO3 can be ascribed to bandgap engineering due to the rotation of Jeff = 1/2 moments. However, theoretical calculations reveal much higher magnetocrystalline anisotropy energy in the film on LaAlO3. This causes difficulties to drive the Jeff = 1/2 moments to reach the diagonal and thereby the metastable state, explaining the distinct anisotropic magnetoresistance between two samples in a qualitative sense. Our findings indicate that strain can be a highly efficient mean to engineer the functionalities of Jeff = 1/2 antiferromagnet Sr2IrO4.

Observation of quantum criticality in antiferromagnetic based (Ce1Y )2Ir3Ge5 Kondo-Lattice system

• The chemical substitution dependencies of the three power law parameters have very similar behavior. • The minimum n exponent, maximum A coefficient, and ρo residual resistivity are at the same critical concentration x cr , expecting the sign for QCP in a non-Fermi Liquid (nFL) region. • Above x cr , the A values drop abruptly and the n values increase only slightly, indicating a transition from strongly to weakly correlated regime near the critical concentration x cr . We have carried out a detailed study of the (Ce 1 −x Y x ) 2 Ir 3 Ge 5 anti-ferromagnetic compounds across the entire range of substitution 0 ≤ x ≤ 0.33 and report the results of powder X-ray diffraction, magnetic susceptibility, heat capacity, and electrical resistivity measurements to exhibit the anti-ferromagnetic phase temperature ( T N ) versus substitution x phase diagram. The pure Ce 2 Ir 3 Ge 5 system indicates anti-ferromagnetic behavior below T N = 9.5 K. Substitution of Y into (Ce 1 −x Y x ) 2 Ir 3 Ge 5 compound leads to a decrease in the anti-ferromagnetic phase temperature ( T N ). Near x = 0.3, the anti-ferromagnetic transition temperature is suppressed to zero kelvin at an apparent anti-ferromagnetic quantum critical point, without the superconductivity sign, where the temperature dependence of the heat capacity and electrical resistivity in this region reveal non-Fermi Liquid behavior. The above results, for example, the suppressing of T N, maybe a new way to find low-temperature superconductivity in these compounds.

Relaxor ferroelectric nature and magnetoelectric coupling of the one dimensional frustrated Ca3CoMnO6

The typical ↑↑↓↓ spin order of the one-dimensional frustrated Ca 3 CoMnO 6 breaks the inversion symmetry and results in the ferroelectricity. But the previous calculations predict a much larger ferroelectric polarization than the experimental observation. To comprehend the divergence, Ca 3 CoMnO 6 ceramics were prepared and the magnetic, dielectric properties were studied. In accordance with the formation of short range magnetic correlation, around the antiferromagnetic transition temperature T N the Ca 3 CoMnO 6 ceramics present weak relaxor ferroelectric nature. It implies the existence of polar nanoregions. Thus, the destruction of long range ferroelectric order and the formed polar nanoregions should be responsible for the suppressed macroscopic ferroelectric polarization. The activation energy and static freezing temperature of Ca 3 CoMnO 6 are also calculated. The obtained values are E a = 6.31 × 10 −3 eV and T f = 1.5 K, respectively. Both of them are lower about two orders of magnitude than the conventional relaxor ferroelectrics. Magnetic field dependent dielectric permittivity manifests the large magnetodielectric coupling of Ca 3 CoMnO 6 . Under the application of field of 7 T, the dielectric permittivity reduces by about 10%. • Around the antiferromagnetic transition temperature T N the Ca 3 CoMnO 6 ceramics present weak relaxor ferroelectric nature. • The Ca 3 CoMnO 6 ceramicspresent weak relaxor ferroelectric nature. • Magnetic field dependent dielectric permittivity manifests the largemagnetodielectric coupling.

Synthesis conditions of off-stoichiometric BaFe9LiO15 polycrystalline and single-crystal samples

We have determined the phase diagrams of BaO-Li2O-Fe2O3 about BaFe9LiO15, which we initially came across with unfamiliar Bragg peaks through our attempts to synthesize a kind of Y-type hexaferrite, Ba2Me2Fe12O22 with Me2 = LiFe. The initial composition of Ba: Fe: Li = 2.5: 23: 2 allowed us to obtain the single phase of BaFe9LiO15 despite its off-stoichiometry. The conditions for the formation of the single phase of BaFe9LiO15 were confirmed by synthesizing about 40 initial composition samples around Ba: Fe: Li = 2.5: 23: 2 at 1000, 1050, and 1100°C, respectively. Single crystals of BaFe9LiO15 were separated from the internal part of a disk-shaped sample with the initial composition of Ba: Fe: Li = 2.5: 23: 2 sintered at 1200°C. X-ray crystallography for a single crystal showed that the oxide has an orthorhombic structure (space group: Cmca) with a = 11.527(8) Å,b = 10.253(7) Å, and c = 9.450(6) Å, which is consistent with the previously-reported Rietveld analysis result of synchrotron-radiation X-ray diffraction experiments on BaFe9LiO15 powder. The temperature dependence of magnetization at μ0H = 0.1 T showed a slight change in slope around 200°C, consistent with the previously-reported antiferromagnetic transition temperature determined by Mössbauer spectroscopy.

Identifying the octupole antiferromagnetic domain orientation in Mn3NiN by scanning anomalous Nernst effect microscopy

The intrinsic anomalous Nernst effect in a magnetic material is governed by the Berry curvature at the Fermi energy and can be realized in non-collinear antiferromagnets with vanishing magnetization. Thin films of (001)-oriented Mn3NiN have their chiral antiferromagnetic structure located in the (111) plane facilitating the anomalous Nernst effect unusually in two orthogonal in-plane directions. The sign of each component of the anomalous Nernst effect is determined by the local antiferromagnetic domain state. In this work, a temperature gradient is induced in a 50 nm thick Mn3NiN two micrometer-size Hall cross by a focused scanning laser beam, and the spatial distribution of the anomalous Nernst voltage is used to image and identify the octupole macrodomain arrangement. Although the focused laser beam width may span many individual domains, cooling from room temperature to the antiferromagnetic transition temperature in an in-plane magnetic field prepares the domain state, producing a checkerboard pattern resulting from the convolution of contributions from each domain. These images together with atomistic and micromagnetic simulations suggest an average macrodomain of the order of 1 μm2.

Rb2FeGe3S8 and Cs2FeGe3S8: New layered chalcogenides in A2MIIMIV3Q8 family with antiferromagnetic property

Two new layered chalcogenides Rb2FeGe3S8 and Cs2FeGe3S8 were designed and synthesized in A2MIIMIV3Q8 family. These two isostructural compounds belong to the monoclinic space group P21/c. Their 2D layer structure was composed of [FeS4] tetrahedra and [GeS4] tetrahedra in the ab plane. The UV–vis diffuse reflectance spectra indicated that their optical band gaps are 1.64 ​eV and 1.80 ​eV, respectively. Magnetic properties research show that Rb2FeGe3S8 and Cs2FeGe3S8 have antiferromagnetic properties, and their antiferromagnetic transition temperatures are TN ​= ​10.77 ​K and 8.64 ​K, respectively.

Vacancy-Induced Temperature-Dependent Thermal and Magnetic Properties of Holmium-Substituted Bismuth Ferrite Nanoparticle Compacts.

Multiferroics have gained widespread acceptance for room-temperature applications such as in spintronics, ferroelectric random access memory, and transistors because of their intrinsic magnetic and ferroelectric coupling. However, a comprehensive study, establishing a correlation between the magnetic and thermal transport properties of multiferroics, is still missing from the literature. To fill the void, this work reports the temperature-dependent thermal and magnetic properties of holmium-substituted bismuth ferrite (BiFeO3) and their dependencies on oxygen vacancies and structural modifications. Two distinct magnetic transitions on temperature-dependent magnetic and heat capacity responses are identified. Experimental analysis suggests that the excess of oxygen vacancies shifts the magnetic transition temperature by ∼64 K. The holmium substitution-induced structural modification increases BiFeO3 heat capacity by 30% up to the antiferromagnetic phase transition temperature. Furthermore, an unsaturated heat capacity even at temperatures as high as 850 K is observed and is ascribed to anharmonicity and partial densification of the nanoparticles used during heat capacity measurements. The room-temperature thermal conductivity of BiFeO3 is ∼0.33 ± 0.11 W m-1 K-1 and remains unchanged at high temperatures due to defect scattering from porosities.

Pressured-induced superconducting phase with large upper critical field and concomitant enhancement of antiferromagnetic transition in EuTe2

We report an unusual pressure-induced superconducting state that coexists with an antiferromagnetic ordering of Eu2+ moments and shows a large upper critical field comparable to the Pauli paramagnetic limit in EuTe2. In concomitant with the emergence of superconductivity with Tc ≈ 3–5 K above Pc ≈ 6 GPa, the antiferromagnetic transition temperature TN(P) experiences a quicker rise with the slope increased dramatically from dTN/dP = 0.85(14) K/GPa for P ≤ Pc to 3.7(2) K/GPa for P ≥ Pc. Moreover, the superconducting state can survive in the spin-flop state with a net ferromagnetic component of the Eu2+ sublattice under moderate magnetic fields μ0H ≥ 2 T. Our findings establish the pressurized EuTe2 as a rare magnetic superconductor possessing an intimated interplay between magnetism and superconductivity.

Ferroquadrupolar ordering in a magnetically ordered state in ErNiAl

We conducted ultrasonic measurements to clarify whether a phase transition exists in ErNiAl, a hexagonal compound, below the antiferromagnetic transition temperature, ${T}_{\mathrm{N}}\ensuremath{\sim}6$ K. We discovered a significant elastic softening of the transverse modulus, ${C}_{66}$, accompanied by a significant ultrasonic attenuation toward ${T}_{\mathrm{Q}}=3.4$ K, which is the temperature of a sharp downward peak in other moduli, indicating a phase transition at ${T}_{\mathrm{Q}}$. The crystal field analysis reveals that the softening of ${C}_{66}$ below 80 K is due to an interlevel ${O}_{xy}$-type quadrupole interaction with a positive quadrupole-quadrupole coupling constant between the ground and excited Kramers doublets. A spontaneous expectation value of ${O}_{xy}$ emerges at ${T}_{\mathrm{Q}}$ in our crystal field model with the mean-field approximation. No quadrupolar ordering occurs in a magnetically ordered state because the degeneracy of quadrupoles is lifted by an internal magnetic field of magnetic ordering. However, our experimental and calculated results suggest that the driving force of the phase transition at ${T}_{\mathrm{Q}}$ is ${O}_{xy}$-type ferroquadrupolar ordering, implying a quadrupolar ordering in a magnetically ordered state at zero magnetic field.