Superexchange Interaction in Insulating EuZn2_{2}P2_{2}

We report magnetic and transport properties of single-crystalline EuZn$_{2}$P$_{2}$, which has trigonal CaAl$_2$Si$_2$-type crystal structure and orders antiferromagnetically at $\approx$23~K. Easy $ab$-plane magneto-crystalline anisotropy was confirmed from the magnetization isotherms, measured with a magnetic field applied along different crystallographic directions ($ab$-plane and $c$-axis). Positive Curie-Weiss temperature indicates dominating ferromagnetic correlations. Electrical resistivity displays insulating behavior with a band-gap of $\approx\,$0.177~eV, which decreases to $\approx\,$0.13~eV upon application of a high magnetic field. We explained the intriguing presence of magnetic interactions in an intermetallic insulator by the mechanism of extended superexchange, with phosphorus as an anion mediator, which is further supported by our analysis of the charge and spin density distributions. We constructed the effective Heisenberg model, with exchange parameters derived from the \textit{ab initio} DFT calculations, and employed it in Monte-Carlo simulations, which correctly reproduced the experimental value of N\'eel temperature

Magnetic and Transport Properties of Possibly Topologically Nontrivial Half-Heusler Bismuthides RMBi (R = Y, Gd, Dy, Ho, Lu; M = Pd, Pt)

High quality single crystals of some representatives of half-Heusler family were grown from Bi-flux. For single crystals characterization, X-ray diffraction and scanning electron microscopy techniques were used. The low-temperature physical properties of the synthesized crystals were determined by means of magnetization, magnetic susceptibility, electrical resistivity and heat capacity measurements. For each compound but LuPtBi, the electrical resistivity varies in a semimetallic manner at high temperatures, and exhibits a metallic character at low temperatures. LuPtBi is metallic in the whole temperature range studied. The bismuthides HoPdBi, LuPdBi, LuPtBi and YPtBi were found superconducting below the critical temperature $T_{c}$ = 0.7, 1.8, 0.9, and 0.96 K, respectively. For the compounds GdPdBi, DyPdBi and HoPdBi, an antiferromagnetic ordering was found to set in below $T_{N}$ = 12.8, 3.7, and 1.9 K, respectively. HoPdBi is thus an intriguing material in which both cooperative phenomena coexist

Magnetic Order and SdH Effect in Half-Heusler Phase ErPdBi

Single crystals of ErPdBi were grown from Bi-flux. The crystal structure of MgAgAs-type was confirmed using X-ray diffraction. Magnetization, magnetic susceptibility, electrical resistance and heat capacity measurements revealed an antiferromagnetic phase transition at $T_{N}$ = 1.2 K. At high temperatures, the electrical resistance has a semiconducting-like character (dR/dT < 0 ). The resistance starts decreasing with decreasing T below 15 K and shows a very sharp drop below $T_{N}$ but remains finite down to 0.4 K. Hence, no obvious evidence of superconductivity was found in the electrical transport data. On the other hand, the real part of AC magnetic susceptibility is negative below $T_{C}$ = 1.6 K and its imaginary component has a clear maximum at this temperature that might be associated with the onset of superconducting state. The electrical resistance revealed Shubnikov-de Haas oscillations in magnetic fields 8-33 T. Their amplitude decreases with increasing T and disappears above 10 K. Cyclotron mass determined from this dependence is 0.21 $m_{e}$

Antiferromagnetic order in the half-Heusler phase TbPdBi

Single crystals of TbPdBi, a representative of the group of half-Heusler bismuthides, were studied by means of magnetic susceptibility, heat capacity, electrical resistivity, magnetostriction and thermal expansion measurements. The compound was characterized as an antiferromagnet with the Néel temperature T_{N} ≈5.3 K. Neutron diffraction experiment confirmed the antiferromagnetic ordering and yielded the propagation vector k=(1/2,1/2,1/2). Remarkably, this k vector is in accord with the recently developed theory of antiferromagnetic topological insulators

Giant Magnetoresistance and Shubnikov-de Haas Effect in LuSb

Single-crystals of LuSb were investigated by means of electrical resistivity and magnetoresistance measurements. The compound was found to exhibit giant magnetoresistance exceeding 3000%, low-temperature resistivity plateau, and Shubnikov-de Haas oscillations. It was characterized as a semimetal with nearly balanced contributions of electron and hole carriers to the magnetotransport properties. The experimental findings, supported by the results of electronic structure calculations, proved that the magnetotransport in LuSb can be described in the scope of 3D multi-band Fermi surface model without topologically non-trivial electronic states

Metamagnetism and crystal-field splitting in pseudohexagonal CeRh₃Si₂

CeRh3Si2 has been reported to exhibit metamagnetic transitions below 5 K, a giant crystal field splitting, and anisotropic magnetic properties from single crystal magnetization and heat capacity measurements. Here we report results of neutron and x-ray scattering studies of the magnetic structure and crystal-field excitations to further understand the magnetism of this compound. Inelastic neutron scattering and resonant inelastic x-ray scattering reveal a Jz = 1/2 ground state for Ce when considering the crystallographic a direction as quantization axis, thus explaining the anisotropy of the static susceptibility. Furthermore, we find a total splitting of 78 meV for the J = 5/2 multiplet. The neutron diffraction study in zero field reveals that, on cooling from the paramagnetic state, the system first orders at TN1 = 4.7 K in a longitudinal spin density wave with ordered Ce moments along the b axis (i.e., the [0 1 0] crystal direction) and an incommensurate propagation vector k = (0, 0.43, 0). Below the lower-temperature transition TN2 = 4.48 K, the propagation vector locks to the commensurate value k = (0, 0.5, 0), with a so-called lock-in transition. Our neutron diffraction study in applied magnetic field H II b axis shows a change in the commensurate propagation vector and development of a ferromagnetic component at H = 3 kOe, followed by a series of transitions before the fully field-induced ferromagnetic phase is reached at H = 7 kOe. This explains the nature of the steps previously reported in field-dependent magnetization measurements. A very similar behavior is also observed for the H II [0 1 1] crystal direction

Metamagnetism and crystal-field splitting in pseudohexagonal CeRh3Si2

CeRh 3 Si 2 has been reported to exhibit metamagnetic transitions below 5 K, a giant crystal field splitting, and anisotropic magnetic properties from single crystal magnetization and heat capacity measurements. Here we report results of neutron and x-ray scattering studies of the magnetic structure and crystal-field excitations to further understand the magnetism of this compound. Inelastic neutron scattering and resonant inelastic x-ray scattering reveal a J z = 1 / 2 ground state for Ce when considering the crystallographic a direction as quantization axis, thus explaining the anisotropy of the static susceptibility. Furthermore, we find a total splitting of 78 meV for the J = 5 / 2 multiplet. The neutron diffraction study in zero field reveals that, on cooling from the paramagnetic state, the system first orders at T N 1 = 4.7 K in a longitudinal spin density wave with ordered Ce moments along the b axis (i.e., the [0 1 0] crystal direction) and an incommensurate propagation vector k = ( 0 , 0.43 , 0 ). Below the lower-temperature transition T N 2 = 4.48 K , the propagation vector locks to the commensurate value k = ( 0 , 0.5 , 0 ) , with a so-called lock-in transition. Our neutron diffraction study in applied magnetic field H ∥ b axis shows a change in the commensurate propagation vector and development of a ferromagnetic component at H = 3 kOe , followed by a series of transitions before the fully field-induced ferromagnetic phase is reached at H = 7 kOe . This explains the nature of the steps previously reported in field-dependent magnetization measurements. A very similar behavior is also observed for the H ∥ [0 1 1] crystal direction

Tuning the parity mixing of singlet-septet pairing in a half-Heusler superconductor

International audienceIn superconductors, electrons with spin s ¼ 1=2 form Cooper pairs whose spin structure is usually singlet (S ¼ 0) or triplet (S ¼ 1). When the electronic structure near the Fermi level is characterized by fermions with angular momentum j ¼ 3=2 due to strong spin-orbit interactions, novel pairing states such as even-parity quintet (J ¼ 2) and odd-parity septet (J ¼ 3) states are allowed. Prime candidates for such exotic states are half-Heusler superconductors, which exhibit unconventional superconducting properties, but their pairing nature remains unsettled. Here, we show that the superconductivity in the noncentrosymmetric half-Heusler LuPdBi can be consistently described by the admixture of isotropic even-parity singlet and anisotropic odd-parity septet pairing, whose ratio can be tuned by electron irradiation. From magnetotransport and penetration depth measurements, we find that carrier concentrations and impurity scattering both increase with irradiation, resulting in a nonmonotonic change of the superconducting gap structure. Our findings shed new light on our fundamental understanding of unconventional superconducting states in topological materials

Physical Review Materials

New materials discovery is the driving force for progress in solid state physics and chemistry. Here we solve the crystal structure and comprehensively study physical properties of ZnVSb in the polycrystalline form. Synchrotron x-ray diffraction reveals that the compound attains a layered ZrSiS-type structure (P4/nmm, a = 4.09021(2) Å, c = 6.42027(4) Å). The unit cell is composed of a 2D vanadium network separated by Zn-Sb blocks that are slightly distorted from the ideal cubic arrangement. A considerable amount of vacancies were observed on the vanadium and antimony positions; the experimental composition is ZnV0.91Sb0.96. Low-temperature x-ray diffraction shows very subtle discontinuity in the lattice parameters around 175 K. Bonding V-V distance is below the critical separation of 2.97 Å known from the literature, which allows for V-V orbital overlap and subsequent metallic conductivity. From ab initio calculations, we found that ZnVSb is a pseudogap material with an expected dominant vanadium contribution to the density of states at the Fermi level. The energy difference between the antiferromagnetic and nonordered magnetic configurations is rather small (0.34 eV/f.u.). X-ray photoelectron spectroscopy fully corroborates the results of the band structure calculations. Magnetic susceptibility uncovered that, in ZnVSb, itinerant charge carriers coexist with a small, localized magnetic moment of ca. 0.25 μB. The itinerant electrons arise from the ordered part of the vanadium lattice. Fractional localization, in turn, was attributed to V atoms neighboring vacancies, which hinder full V-V orbital overlap. Furthermore, the susceptibility and electrical resistivity showed a large hysteresis between 120 K and 160 K. The effect is not sensitive to magnetic fields up to 9 T. Curie-Weiss fitting revealed that the amount of itinerant charge carriers in ZnVSb drops with decreasing temperature below 160 K, which is accompanied by a concurrent rise in the localized magnetic moment. This observation together with the overall shape of the hysteresis in the resistivity allows for suggesting a plausible origin of the effect as a charge-transfer metal-insulator transition. Ab initio phonon calculations show the formation of a collective phonon mode at 2.8 THz (134 K). The experimental heat capacity reflected this feature by a boson peak with Einstein temperature of 116 K. Analysis of the heat capacity with both an ab initio perspective and Debye-Einstein model revealed a sizable anharmonic contribution to heat capacity, in line with disordered nature of the material. Further investigation of the electron and phonon properties for ZnVSb is likely to provide valuable insight into the relation between structural disorder and the physical properties of transition-metal-bearing compounds. © 2021 American Physical Society