Pyrochlore Oxide Hg2Os2O7 on Verge of Metal–Insulator Boundary

Semimetallic osmium pyrochlore oxide Cd2Os2O7 undergoes a magnetic transition to an all-in-all-out (AIAO)-type order at 227 K, followed by a crossover to an AIAO insulator at around 210 K. Here, we studied the isostructural and isoelectronic compound Hg2Os2O7 through thermodynamic measurements, µSR spectroscopy and neutron diffraction experiments. A similar magnetic transition, probably to an AIAO-type order, was observed at 88 K, while the resistivity showed a decrease at the transition and remained metallic down to 2 K. Thus, the ground state of Hg2Os2O7 is most likely an AIAO semimetal, which is analogous to the intermediate-temperature state of Cd2Os2O7. Hg2Os2O7 exists on the verge of the metal–insulator boundary on the metal side and provides an excellent platform for studying the electronic instability of 5d electrons with moderate electron correlations and strong spin–orbit interactions.

A new device for autonomous space devices based on a three-component quantum variometer

The necessity of additional study of magnetic field variations in the magnetic transition layer, in the magnetopause, as well as in the plasma layer and in the tail of the magnetosphere in a wide range of distances from the Earth is substantiated. To obtain additional information in comparison with the studies that are being carried out in outer space at the present time, it is necessary to simultaneously monitor the magnetic field at various points in outer space. It is also necessary to register the dynamics of changes in the magnetic field in time in space by three components. To accomplish this task, a small-sized three-component quantum variometer with autonomous power supply has been developed for space devices, which can be lost in the course of short-term research. The results of the operation of a quantum variometer are presented.

Reconfigurable single-material Peltier effect using magnetic-phase junctions

Peltier effects, which produce a heat flux at the junction of two different materials, have been an important technology for heating and cooling by electrical means. Whereas Peltier devices have advantages such as cleanliness, silence, compactness, flexibility, reliability, and efficiency, relatively complicated modular structures are unavoidable, leading to a higher cost than that of commonly used refrigeration technology. Here, we provide a concept of a Peltier device composed of a single magnetic material exhibiting a first-order magnetic transition. Our concept is based on a controllable junction structure consisting of two magnetic phases with opposite Peltier coefficients instead of a semiconductor junction. Using $${\mathrm{Mn}}_{1.96}{\mathrm{Cr}}_{0.04}\mathrm{Sb}$$ Mn 1.96 Cr 0.04 Sb samples with the first-order magnetic transition between ferrimagnetic (FI) and antiferromagnetic (AF) states, we successfully made a stable junction structure of AF/FI/AF by a pulse heating method and achieved a maximum Peltier coefficient of 0.58 mV. Our device concept was further verified by a numerical simulation based on a finite element method. The single-material Peltier effect reported here avoids a complex device design involving material junctions and is importantly reconfigurable.

Coexistence of ferromagnetism and superconductivity in MWCNT/Bi2SiO5 nanocomposites

This work explores the temperature and field-dependent magnetic properties of Bi2SiO5 (BSO)/multiwall carbon nanotube (MWCNT) nanocomposites prepared by hydrothermal method using different content of magnetic MWCNT (from 1 to 20 wt%). A pure BSO prepared by the same method was also studied as a reference. Phase purity and structure of the pure BSO and CBSO nanocomposites were analyzed by employing the Rietveld refinement of an X-ray diffraction pattern. DC magnetization analysis confirms the co-existence of multiple magnetic phases in CBSO nanocomposites, where a paramagnetic (PM) to ferromagnetic (FM) transition experiences at ~33 K, and a cluster spin glass behavior at near Curie temperature (i.e., TC ~25 K). A weak superconducting transition (TSC) at around ~23 K was observed for all the CBSO nanocomposites samples (i.e., 2.5 wt% MWCNT and above samples). Moreover, a novel feature of these nanocomposites is that they exhibit a complex magnetism corresponding to the co-existence of ferromagnetism and superconductivity. This behavior can be exploited to engineer a magnetic CBSO composites system with the magnetic transition tune by compositional structure, with interesting potential applications.

Effect of Co and Mg doping at Cu site on structural, magnetic and dielectric properties of α-Cu2V2O7

We have studied the effect of doping of both magnetic (Co) and nonmagnetic (Mg) ions at the Cu site on phase transition in polycrystalline α-Cu2V2O7 through structural, magnetic, and electrical measurements. x-ray diffraction reveals that Mg doping triggers an onset of α- to β-phase structural transition in Cu2−xMgxV2O7 above a critical Mg concentration xc=0.15, and both the phases coexist up to x=0.25. Cu2V2O7 possesses a non-centrosymmetric(NCSM) crystal structure and antiferromagnetic (AFM) ordering along with a non-collinear spin structure in the α phase, originated from the microscopic Dzyaloshinskii-Moriya(DM) interaction between the neighboring Cu spins. Accordingly, a weak ferromagnetic behavior has been observed up to x=0.25. However, beyond this concentration, Cu2−xMgxV2O7 exhibits complex magnetic properties. A clear dielectric anomaly is observed in α-Cu2−xMgxV2O7 around the magnetic transition temperature, which loses its prominence with the increase in Mg doping. The analysis of experimental data shows that the magnetoelectric coupling is nonlinear, which is in agreement with the Landau theory of continuous phase transitions. Co doping, on the other hand, initiates a sharp α to β phase transition around the same critical concentration xc=0.15 in Cu2−xCoxV2O7 but the ferromagnetic behavior is very weak and can be detected only up to x=0.10. We have drawn the magnetic phase diagram which indicates that the rate of suppression in transition temperature is the same for both types of doping, magnetic (Co) and nonmagnetic (Zn/Mg).

Fеatures of exchange interactions of the B-sublattice ions in the La0,5Sr0,5Co1–x Nix O3–d system

A comprehensive study of the crystal structure, magnetic and magnetotransport properties of the La0.5Sr0.5Co1–x Nix O3–d cobaltite system (x = 0.1–0.16) was carried out. The X-ray measurement results indicate that the unit cell of all solid solutions of the system is cubic and is described by the space group Pm3m. It is found that with an increase in the 540 Doklady of the National Academy of Sciences of Belarus, 2021, vol. 65, no. 5, рр. 539–545 Ni content, the Curie temperature (TC) decreases from 230 to 180 K, as well as magnetization values. The magnetic transition is blurred across the field. The iodometric studies show that the concentration of Co4+ ions in all samples does not exceed 35 %. The chemical substitution of Co ions by Ni ones does not result in significant modification of the unit cell parameters, which may indicate a spin crossover of Co ions. The temperature dependence of resistivity is metallic in character, which indicates the stability of the main conducting ferromagnetic phase. The nature of exchange interactions of different signs between B-sublattice ions completely determines the behavior of the system. An increase in the content of Ni ions leads both to decrease the component of ferromagnetic exchange interactions between Co3+ ions in the intermediate spin state and to increase the fraction of antiferromagnetic and weaker ferromagnetic interactions. In addition, presumably the Co4+ ion can stabilize the high spin state of the closestCo3+ ion and in the next two coordination spheres it can stabilize the Co3+ ion in the low spin state, i. e. the ferromagnetic complexes Co4+–Co3+ (HS) are shielded by the diamagnetic shell of low spin Co3+ ions, which results in decreasing the magnetization values.