Magnetization and specific heat of the dimer system CuTe2O5

We report on magnetization and specific heat measurements on single-crystalline CuTe2O5. The experimental data are directly compared to theoretical results for two different spin structures, namely an alternating spin-chain and a two-dimensional (2D) coupled dimer model, obtained by Das et al. [Phys. Rev. B 77, 224437 (2008)]. While the analysis of the specific heat does not allow to distinguish between the two models, the magnetization data is in good agreement with the 2D coupled dimer model.Comment: 5 pages, 3 figure

Flux crystal growth of Cu<inf>2</inf>GaBO<inf>5</inf> and Cu<inf>2</inf>AlBO<inf>5</inf>

© 2020 Elsevier B.V. The results of growth of two oxyborate single crystals, Cu2GaBO5 and Cu2AlBO5, with ludwigite structure from different flux systems using the spontaneous nucleation technique are reported. We obtained large Cu2GaBO5 and Cu2AlBO5 crystals of dimensions up to 3 × 4 × 15 mm3 and 1 × 1 × 10 mm3, respectively. Trimolybdate-bismuth fluxes diluted with the sodium carbonate for both Cu2GaBO5 and Cu2AlBO5, as well as lithium-molybdate and lithium-borate fluxes for Cu2AlBO5, were used. It was observed that the growth of Cu2GaBO5 and Cu2AlBO5 is accompanied by the growth of CuO, Cu2Al6B4O17, and Cu2Al1-xGaxBO5 crystals as secondary phases. Structural and magnetic characterization of the crystals is also performed

Magnetic properties of ludwigite Mn<inf>2.25</inf>Co<inf>0.75</inf>BO<inf>5</inf>

Needle-shape single crystals of Mn2.25Co0.75BO5 ludwigite were synthesized by the flux technique and investigated by means of X-ray diffraction, static magnetic susceptibility and specific heat measurements. Magnetization and specific heat experiments showed the presence of ferrimagnetic ordering near TN≃61K. Below this temperature the magnetic properties demonstrated the angular dependence and the high magnetic hardness in a magnetic field applied perpendicular to the crystallographic c axis, which is similar to other cobalt-containing ludwigites. The effective magnetic moment per magnetic ion 4.8μB was calculated from the paramagnetic data. Analysis of the phonon contribution to the specific heat allowed to distinguish the magnetic contribution CM, which has two features. One of which was observed at TN and can be attributed to strong exchange interactions between spins of magnetic ions. The second one at T = 11.6 K is due to the effect of the ligands crystal field on a magnetic ion with S>1∕2

Synthesis, structure, magnetic behavior and dielectric relaxation of the La<inf>x</inf>Sr<inf>2-x</inf>Fe<inf>х</inf>Ti<inf>1-х</inf>O<inf>4</inf> (х ​= ​0.5, 0.7) oxide ceramic

© 2020 Elsevier Inc. This study is devoted to the investigation of the high dielectric constant causes in complex oxides with a structure of the K2NiF4 type. А new thermobaric treated ceramics on the basis conjugate LaxSr2-xFeхTi1-хO4 (х ​= ​0.5, 0.7) solid solutions was synthesized and the study their structure, microstructure, magnetic and dielectric properties was performed. It is shown that antiferromagnetic interactions coexist with ferromagnetic, which become dominant towards to low temperatures; the appearance of two types of magnetic interactions may be related to the presence of magnetic ions of different valences. Different values of the dielectric constants ε are observed in wide region of frequencies 10–107 ​Hz. In obtained at ambient pressure LaxSr2-xFeхTi1-хO4 (х ​= ​0.5, 0.7) ceramics the highest permittivity ε value is only 30–50 in the frequency range from 1 ​kHz to 1 ​MHz. After the samples treatment at 1273 ​K and P ​= ​4 ​GPa during 5 ​min ε increases to 5–102–103 ​at 293 ​К and independent of frequency in the range (102–106) Hz. At the temperature increase the permittivity as well increases and the ε value becomes ~106 at, approximately, f ​= ​100 ​Hz and T ​= ​750 ​K. An obvious change of samples microstructure and polyhedra structure anisotropy in LaxSr2-xFeхTi1-хO4 (х ​= ​0.5, 0.7) was observed after the thermobaric treatment. Described in this article performed dielectric properties investigations indicate that possible reasons of the high-permittivity origin are specifics of layered structure, microstructure and charge polarization associated with it, Maxwell-Wagner polarization at the grain boundaries and inhomogeneities and small polaron hopping conduction mechanism

Structure, magnetic and thermodynamic properties of heterometallic ludwigites: Cu<inf>2</inf>GaBO<inf>5</inf> and Cu<inf>2</inf>AlBO<inf>5</inf>

© 2020 Elsevier B.V. We present an extensive study of the structural, magnetic and thermodynamic properties of high-quality monocrystals of two heterometallic oxyborates from the ludwigite family: Cu2GaBO5 and Cu2AlBO5 in the temperature range above 2 K. The distinctive feature of the investigated structures is the selective distribution of Cu and Ga/Al cations. The unit cell of Cu2GaBO5 and Cu2AlBO5 contains four nonequivalent crystallographic sites of metal ions. Two sites in the structure of Cu2GaBO5 are fully occupied by Cu atoms which form the quasi one-dimensional chains along the a-axis. For Cu2AlBO5 all sites are partially occupied by Al and Cu atoms. The joint analysis of low-temperature data on magnetic susceptibility and magnetic contribution to the specific heat showed that Cu2AlBO5 and Cu2GaBO5 exhibit an antiferromagnetic transition at TN=2.4 and 4.1 K, respectively. The magnetic response below TN can be represented as the sum of two contributions: the ordered component and the paramagnetic contribution from defects of the same relative weight. It is shown that the external magnetic field above 2.5 T and 2.8 T for Cu2GaBO5 and Cu2AlBO5, respectively, leads to a broadening of the magnetic phase transition indicating suppression of the long-range antiferromagnetic order

Iron oxidation state in La<inf>0.7</inf>Sr<inf>1.3</inf>Fe<inf>0.7</inf>Ti<inf>0.3</inf>O<inf>4</inf> and La<inf>0.5</inf>Sr<inf>1.5</inf>Fe<inf>0.5</inf>Ti<inf>0.5</inf>O<inf>4</inf> layered perovskites: Magnetic properties

La0.5Sr1.5Fe0.5Ti0.5O4 and La0.7Sr1.3Fe0.7Ti0.3O4 solid solutions with the layered perovskite structure were synthesized using a solid state method. Structural properties of obtained samples were characterized using X-ray diffraction and X-ray fluorescence analyses. Magnetic properties were investigated using magnetometry, electron spin resonance (ESR) and Mössbauer spectroscopy methods. Based on magnetization and ESR measurements it was suggested the presence of Fe4+ ions in addition to trivalent iron ions that was exactly confirmed by Mössbauer spectroscopy investigations. Based on all experimental results one can suggest the presence of the electronic phase separation in the investigated samples – the simultaneous existence of the paramagnetic phase and magnetically correlated regions, which form due to the mixed-valence iron ions. So the paramagnetic phase with strong antiferromagnetic correlation exists in both samples, while the second phase is ferromagnetically and ferrimagnetically correlated regions in La0.5Sr1.5Fe0.5Ti0.5O4 and La0.7Sr1.3Fe0.7Ti0.3O4, respectively

Analysis of nanostructured cobalt ion beam-modified Ge surface for high capacity Li-ion battery anodes by X-ray photoelectron spectroscopy

© 2020 Published under licence by IOP Publishing Ltd. The results of the study of nanostructured germanium (Ge), intended for its subsequent use as electrodes of lithium-ion batteries are presented. Single-crystal germanium plate was irradiated by cobalt ions with an energy of 40 keV in the dose 4×1016 Co+ / cm2 for the nanostructuring. The changes in the elemental composition occurring during the electrochemical lithiation of manufactured germanium electrode were investigated by X-ray photoelectron spectroscopy (XPS)

Magnetic properties and vanadium oxidation state in α-Li<inf>3</inf>V<inf>2</inf>(PO<inf>4</inf>)<inf>3</inf>/C composite: Magnetization and ESR measurements

Here we present the magnetization and electron spin resonance (ESR) measurements of α-Li3V2(PO4)3/C composite, which can be potentially used as a cathode material in a lithium ion battery. Magnetization measurements of α-Li3V2(PO4)3/C indicate that the investigated sample is in paramagnetic state and exhibits Curie-Weiss like behavior above T = 50K. The negative value of the Curie-Weiss temperature θCW = −22 K suggests the presence of the antiferromagnetic interactions between magnetic spins of V3+ ions (3 d2, S = 1). At the same time, the presence of the magnetic phase transition was not observed in the investigated temperature range from 2 K up to room temperature. The nonlinear behavior of the field dependence of the magnetization was observed only at T = 2 K suggesting the possible magnetic ordering below this temperature. ESR measurements were performed both for as-prepared α-Li3V2(PO4)3/C composite and for α-Li3V2(PO4)3/C sample after Li deintercalation and intercalation processes. The complete reduction of vanadium ions to the initial valence state V3+ after the first charge/discharge cycle was determined indicating the reversible intercalation of all lithium ions to the structure during the first delithiation/lithiation cycle in the investigated α-Li3V2(PO4)3/C composite

Formation of Pores in Thin Germanium Films under Implantation by Ge⁺ Ions

© 2020, Pleiades Publishing, Ltd. Abstract: Results are presented of a study of the morphology of germanium films nanostructured by ion implantation. Film samples were grown by magnetron sputtering in an ultrahigh-vacuum installation and then irradiated with 40 keV Ge+ ions at fluences in the range of (1.8–8) × 1016 ions/cm2. Scanning electron microscopy demonstrated that vacancy complexes with diameters of ~50–150 nm are gradually formed in the bulk of implanted germanium with increasing implantation fluence. After a certain implantation fluence is reached, the complexes emerge on the surface, thereby forming a developed surface profile of the irradiated films