Low-temperature Magnetization Data Research Articles

Mineralogical, magnetic and geochemical data constrain the pathways and extent of weathering of mineralized sedimentary rocks

The oxidative weathering of sulfidic rock can profoundly impact watersheds through the resulting export of acidity and metals. Weathering leaves a record of mineral transformation, particularly involving minor redox-sensitive phases, that can inform the development of conceptual and quantitative models. In sulfidic sedimentary rocks, however, variations in depositional history, diagenesis and mineralization can change or overprint the distributions of these trace minerals, complicating the interpretation of weathering signatures. Here we show that a combination of bulk mineralogical and geochemical techniques, micrometer-resolution X-ray fluorescence microprobe analysis and rock magnetic measurements, applied to drill core samples and single weathered fractures, can provide data that enable the development of a geochemically consistent weathering model.This work focused on one watershed in the Upper Colorado River Basin sitting within the Mesaverde Formation, a sedimentary sandstone bedrock with disseminated sulfide minerals, including pyrite and sphalerite, that were introduced during diagenesis and subsequent magmatic-hydrothermal mineralization. Combined analytical methods revealed the pathways of iron (Fe), carbonate and silicate mineral weathering and showed how pH controls element retention or release from the actively weathering fractured sandstone. Drill core logging, whole rock X-ray diffraction, and geochemical measurements document the progression from unweathered rock at depth to weathered rock at the surface. X-ray microprobe analyses of a 1-cm size weathering profile along a fracture surface are consistent with the mobilization of Fe(II) and Fe(III) into acidic pore water from the dissolution of primary pyrite, Fe-sphalerite, chlorite, and minor siderite and pyrrhotite. These reactions are followed by the precipitation of secondary minerals such as of goethite and jarosite, a Fe-(oxyhydr)oxide and hydrous Fe(III) sulfate, respectively. Microscale analyses also helped explain the weathering reactions responsible for the mineralogical transformations observed in the top and most weathered section of the drill core. For example, dissolution of feldspar and chlorite neutralizes the acidity generated by Fe and sulfide mineral oxidation, oversaturating the solution in both Fe-oxides. The combination of X-ray spectromicroscopy and magnetic measurements show that the Fe(III) product is goethite, mainly present either as a coatings on fracture surfaces in the actively weathering region of the core or more homogeneously contained within the unconsolidated regolith at the top of the core. Low-temperature magnetic data reveal the presence of ferromagnetic Fe-sulfide pyrrhotite that, although it occurs at trace concentrations, could provide a qualitative proxy for unweathered sulfide minerals because the loss of pyrrhotite is associated with the onset of oxidative weathering. Pyrrhotite loss and goethite formation are detectable through room-temperature magnetic coercivity changes, suggesting that rock magnetic measurements can determine weathering intensity in rock samples at many scales. This work contributes evidence that the weathering of sulfidic sedimentary rocks follows a geochemical pattern in which the abundance of sulfide minerals controls the generation of acidity and dissolved elements, and the pH-dependent mobility of these elements controls their export to the ground- and surface-water.

Crystal electric field and possible coupling with phonons in Kondo lattice CeCuGa3

We investigate the magnetic and crystal electric field (CEF) states of the Kondo lattice system CeCuGa3 by muon spin relaxation (muSR), neutron diffraction, and inelastic neutron scattering (INS) measurements. A noncentrosymmetric BaNiSn3-type tetragonal crystal structure (space group I4mm) is inferred from x-ray as well as from neutron powder diffraction. The low-temperature magnetic susceptibility and heat capacity data show an anomaly near 2.3 - 2.5~K associated with long range magnetic ordering, which is further confirmed by muSR and neutron diffraction data. The neutron powder diffraction collected at 1.7 K shows the presence of magnetic Bragg peaks indexed by an incommensurate magnetic propagation vector k = (0.148, 0.148, 0) and the magnetic structure is best described by a longitudinal spin density wave with ordered moments lying in ab-plane. An analysis of the INS data based on a CEF model reveals the presence of two magnetic excitations near 4.5 meV and 6.9 meV. The magnetic heat capacity data suggest an overall CEF splitting of 20.7 meV, however the excitation between 20 and 30 meV is very broad and weak in our INS data, but could provide an evidence of CEF level in this energy range in agreement with the magnetic entropy. Our analysis of INS data based on the CEF-phonon model indicates that the two excitations at 4.5 meV and 6.9 meV have their origin in CEF-phonon coupling (i.e. splitting of one CEF peak into two peaks, called vibron), with an overall splitting of 28.16 meV, similar to the case of CeCuAl3 and CeAuAl3.

Reciprocating Thermal Behavior in Multichannel Relaxation of Cobalt(II) Based Single Ion Magnets

A series of mononuclear Co(II) complexes showing slow magnetic relaxation is assessed from the point of view of relaxation mechanisms. In certain cases, the reciprocating thermal behavior is detected: On cooling, the slow relaxation time is prolonged until a certain limit and then, unexpectedly, is accelerated. The low-temperature magnetic data can be successfully fitted by assuming Raman and/or phonon bottleneck mechanisms of the slow magnetic relaxation for the high-frequency relaxation channel. An additional term with the negative temperature exponent is capable of reproducing the whole experimental dataset.

Evidence of Weak Ferromagnetism, Space Charge Polarization, and Metal to Insulator Transition in Dy-Doped CaMnO3

The effect of Dy doping on CaMnO3 (CDMO) has been thoroughly investigated. The room-temperature structure, low-temperature magnetic transitions, and high-temperature electrical properties of CDMO were studied using X-ray diffraction, magnetization, and dielectric techniques. The CDMO exhibits an orthorhombic structure with Pnma symmetry. The low-temperature magnetic susceptibility data show the ferromagnetic domains embedded in the antiferromagnetic structure (G-type), and it confirms the Neel temperature (TN) approximately 55 K. Temperature-dependent dielectric data measured using a few selected frequencies show a high dielectric constant ~ 29,108,808 at 1 kHz. The presence of a high dielectric constant at the lower frequency side can be attributed to the space charge polarization (SCP) and compositional disorder (heterogeneity) in the compounds. The impedance cole-cole plot shows a depressed semicircle; mathematically these data were fitted by the Kohlrausch-Williams-Watt model. From this model obtained two mechanisms: (i) the electric modulus divulges the CDMO ceramic tails the Non-Debye type of relaxation and (ii) the electric modulus peak shifting evidence the charge carrier mobility from long range to short range. High-temperature dielectric, resistivity, and conductivity data show a clear anomaly around 461 K, owing to metal to insulator transition.

Comprehensive structural and magnetic properties of iron oxide nanoparticles synthesized through chemical routes

Magnetite (Fe3O4) is one of the most widely explored ceramic materials for the applications in various industrial and biomedical levels. Applications towards specific field require tuning of its properties, which can be modulated by controlling particle size as well as different synthesis parameters and conditions. In present work, we have chosen six different chemical synthesis routes and performed a comparative study on variations in structural and physical properties. Present results show that all the synthesis methods provide particles of nanometer range, but the average size of the particle and particle size distribution is different for each method. Present analyses of room temperature and low temperature magnetic data confirm the possibility of presence of superparamagnetic state in 6–8 nm particles. Moreover, the interaction effects are dominant above blocking temperature. From the magnetization data it is also shown how the exchange term evolves as the particle size increases. Additionally, high temperature magnetic measurements are also carried out to compare size dependent magnetic response towards increasing temperature. Since the finite size effects dominate in this range of particles, we believe present study can provide a guideline to choose particular synthesis method for specific application.

Impact of Gd Doping on the Microstructural-, Electronic-, Magnetotransport, and Magnetic Properties of Pr0.6Gd0.1Sr0.3MnO₃ Nanomanganite.

Gadolinium doping effects on structural-, electronic transport and magnetic properties of Pr0.6Gd0.1Sr0.3MnO₃ (PGSMO) nanomanganite (40-65 nm) have been investigated. We have considered the core-shell structure of our PGSMO nanoparticles, which can explain its intriguing magnetic and transport properties. It is reported 65 nm sample exhibits higher metal to insulator transition temperature, TP (∼215 K) and less resistive behavior compare to its nano counterparts. Enhanced low-field magnetoresistance (LFMR) is observed with a reduction of particle size; however maximum change in magnetoresistance (MR), ∼72% is recorded for 65 nm sample around TP at 60 kOe field. Low-temperature magnetization data reveals the existence of glassy phase in the compound. It is revealed that substitution of optimal Gd doping at A site on nanometric scale promotes exotic magnetic and transport properties on nanoscale without adding any external physical perturbation or introducing any significant lattice distortion.

Spin-singlet formation in the spin-tetramer layered organic-inorganic hybridCH3NH3Cu2Cl5

We report spin-singlet formation in an organic-inorganic hybrid identified as ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}{\mathrm{Cu}}_{2}{\mathrm{Cl}}_{5}$. The hybrid adopts a layered structure in which ${{\mathrm{Cu}}_{2}{\mathrm{Cl}}_{5}}^{\ensuremath{-}}$ layers are separated by ${{\mathrm{CH}}_{3}{\mathrm{NH}}_{3}}^{+}$ layers. The inorganic layers consist of corner- and edge-sharing ${\mathrm{CuCl}}_{6}$ octahedra, forming edge-sharing tetramers. Magnetic susceptibility measurements indicate strong antiferromagnetic interactions within the tetramers, whereas the coupling between the tetramers is weak. Low-temperature magnetic susceptibility data as well as electron spin resonance measurements suggest a nonmagnetic ground state with a large spin gap of $\ensuremath{\sim}130\phantom{\rule{0.28em}{0ex}}\mathrm{K}$, in apparent contradiction with ferromagnetic interactions between nearest-neighbor spins. We discuss a spin-tetramer model in which antiferromagnetic next-nearest-neighbor interactions lead to a spin-singlet state.

Mechanochemical synthesis, structural, magnetic, optical and electrooptical properties of CuFeS2 nanoparticles

The rapid mechanochemical synthesis of nanocrystalline CuFeS2 particles prepared by high-energy milling for 60 min in a planetary mill from copper, iron and sulphur elements is reported. The CuFeS2 nanoparticles crystallize in tetragonal structure with mean crystallite size of about 38 ± 1 nm determined by XRD analysis. HRTEM study also revealed the presence of nanocrystals with the size of 5–30 nm with the tendency to form agglomerates. The Raman spectrum confirms the chalcopyrite structure. Low temperature magnetic data for CuFeS2 support the coexistence of antiferromagnetic and paramagnetic spin structure. Moreover, the hysteresis loops taken at temperatures from 5 K to 300 K revealed a presence of very small amount of ferromagnetic phase, which seems to be associated with the non-consumed elemental Fe in as-prepared nanoparticles. The optical band gap of CuFeS2 nanoparticles has been detected to be 1.05 eV, larger than band gap of the bulk material. The wider gap possibly resulted from the nano-size effect. Photoresponses of CuFeS2 nanoparticles were confirmed by I-V measurements under dark and light illumination. It was demonstrated that mechanochemical synthesis can be successfully employed in the one step preparation of nanocrystalline CuFeS2 with good structural, magnetic, optical and electrooptical properties.

Structural, Magnetization and Spin Wave Analysis in Layered 5d Iridate Sr2IrO4

Magnetic behavior has been studied in 5d layered compound Sr2IrO4. The material shows reasonable spin-orbit coupling effect. A canted type antiferromagnetic spin ordering induced by Dzyaloshinskii-Moriya antisymmetric interaction arising from IrO6 octahedral distortion is observed. Our structural analysis shows a rotation of IrO6 octahedra by ∼11.3° around c axis which works as precursor for (canted) weak ferromagnetic phase. Temperature dependant magnetization shows transition temperature ∼225 K and field dependent magnetization shows low moment 0.055 μB/f.u. Our spin-wave analysis of low temperature magnetization data shows very high stiffness constant ∼3365 meVÅ2, which is interesting for this low moment spin canting system.

Structural and Microstructural Correlations of Physical Properties in Natural Almandine-Pyrope Solid Solution: Al70Py29

Garnets are naturally occurring minerals with the general formula X3Y2Z3O12 having various applications. In the present study, the structural and physical properties of a garnet mineral obtained from Indian Rare Earth Ltd., Manavalakurichi, Tamil Nadu, India were comprehensively investigated. The compositional analysis using electron probe micro analysis (EPMA) revealed that the mineral belongs to almandine-pyrope solid solution (Al70Py29) with the chemical formula (Fe1.72Mg0.8Mn0.01Ca0.02) (Fe0.04Al2.36) Si2.93O12. Rietveld refinement of the x-ray diffraction pattern confirms that the space group is $$ Ia{ - }\overline{3} d $$ with refined cubic lattice parameter a = 11.550(4) A. The refined occupancy values of multiple cations in the dodecahedral and octahedral sites are in agreement with the EPMA data. Fourier transform infrared and FT Raman spectra show bands corresponding to almandine-pyrope solid solution. Peak splitting of IR and Raman bands confirms presence of multiple cations in the dodecahedral site. Thermogravimetric/differential thermal analysis shows that the mineral is stable up to 600°C in spite of the presence of Fe2+ ions. Low temperature magnetic susceptibility data is in agreement with the amount of Fe2+ ions present in the mineral. The dielectric constant of the mineral varied from 6 to 16.5 when sintered at temperatures ranging from 600°C to 1250°C.

Carbonate-Bridged Lanthanoid Triangles: Single-Molecule Magnet Behavior, Inelastic Neutron Scattering, and Ab Initio Studies.

Optimization of literature synthetic procedures has afforded, in moderate yield, homogeneous and crystalline samples of the five analogues Na11[{RE(OH2)}3CO3(PW9O34)2] (1-RE; RE = Y, Tb, Dy, Ho, and Er). Phase-transfer methods have allowed isolation of the mixed salts (Et4N)9Na2[{RE(OH2)}3CO3(PW9O34)2] (2-RE; RE = Y and Er). The isostructural polyanions in these compounds are comprised of a triangular arrangement of trivalent rare-earth ions bridged by a μ3-carbonate ligand and sandwiched between two trilacunary Keggin {PW9O34} polyoxometalate ligands. Alternating-current (ac) magnetic susceptibility studies of 1-Dy, 1-Er, and 2-Er reveal the onset of frequency dependence for the out-of-phase susceptibility in the presence of an applied magnetic field at the lowest measured temperatures. Inelastic neutron scattering (INS) spectra of 1-Ho and 1-Er exhibit transitions between the lowest-lying crystal-field (CF) split states of the respective J = 8 and (15)/2 ground-state spin-orbit multiplets of the Ho(III) and Er(III) ions. Complementary ab initio calculations performed for these two analogues allow excellent reproduction of the experimental magnetic susceptibility and low-temperature magnetization data and are in reasonable agreement with the experimental INS data. The ab initio calculations reveal that the slight difference in coordination environments of the three Ln(III) ions in each complex gives rise to differences in the CF splitting that are not insignificant. This theoretical result is consistent with the observation of multiple relaxation processes by ac magnetic susceptibility and the broadness of the measured INS peaks. The ab initio calculations also indicate substantial mixing of the MJ contributions to the CF split energy levels of each Ln(III) ion. Calculations indicate that the CF ground states of the Ho(III) centers in 1-Ho are predominantly comprised of contributions from small MJ, while those of the Er(III) centers in 1-Er are predominantly comprised of contributions from large MJ, giving rise to slow magnetic relaxation. Although no direct evidence for intramolecular RE···RE magnetic coupling is observed in either magnetic or INS studies, on the basis of the ab initio calculations, we find noncollinear magnetic axes in 1-Er that are coplanar with the erbium triangle and radially arranged with respect to the triangle's centroid; thus, we argue that the absence of magnetic coupling in this system arises from dipolar and antiferromagnetic superexchange interactions that cancel each other out.

Magnetic Properties of Helicobacter Pylori Ferritins Genetically Prepared Under Different Biomineralization Conditions

Magnetic properties of bio-magnetic molecule ferritin have been investigated. Two ferritin samples were synthesized under different magnetic fields, 0 and 9.4 T, respectively. This work is focused on the influence of magnetic field on biomineralization process. While magnetization vs. temperature (M-T) data of both samples measured at 1000 Oe are almost identical except for low temperature region (T ＜ 6 K), magnetization vs. field (M-H) data show noticeable difference. From an analysis of M-H data by using a modified Langevin function, we could extract the saturation magnetization m₀(T), the effective magnetic moment μeff (T) and the linear susceptibility χ(T). The difference between the samples is most prominent in the χ(T), whereby the χ(T) of the sample prepared at 9.4 T is 1.7 times bigger than that of the other. In addition, from hysteresis and relaxation measurements, we found the sample prepared at 9.4 T showed strikingly smaller coercivity and slower relaxation.

Temperature dependence of FMR and magnetization in nanocrystalline zinc ferrite thin films

Single phase nano-crystalline zinc ferrite thin films were deposited by RF-magnetron sputtering on quartz substrate at room temperature (RT) in pure Argon environment and annealed (in air) at different temperatures. Temperature dependence of magnetization was studied on these films using both VSM and by observing FMR (in X band). Value of exchange stiffness constant (D) was obtained by fitting Bloch’s law to the low temperature magnetization data. The value of D decreased monotonously with the annealing temperature (TA) of the samples. A film annealed at TA = 523 K, exhibited the highest magnetization value. The FMR line width of the films decreased with increase in measurement temperature. At RT (∼293 K), the lowest value of line width (ΔH) was 15 kA/m and 13 kA/m in parallel and perpendicular configuration respectively for the sample annealed at TA = 623 K.

On the dynamics of the reentrant spin-glass state of the Fe100−xZrx (x = 9, 10) amorphous alloys

Low temperature magnetization (M) and ac susceptibility (χac) data were used to investigate the reentrant spin-glass state in lengths of melt-spun ribbons of Fe100−xZrx (x = 9, 10) amorphous alloys. The temperature range investigated was from 2 to 300 K, while the applied magnetic field H was varied in the range of ±85 kOe. The magnetic properties were found to be strongly influenced by the sample composition despite the fact that the amount of Fe varies by 1 at. %. For instance, the Curie temperature (TC) is reduced from 232.5 K to 213.0 K with decreasing Fe concentration, while M for the lower Fe concentration, measured at the highest applied magnetic field (H = 85 kOe) was nearly double the value for that of the higher; the coercivity in the ferromagnetic regime is reduced by a factor close to five when x is increased from 9 at. % to 10 at. %. The ac susceptibility measured for frequencies f in the range of 10–104 Hz showed a sharp drop in the magnitude of the in-phase contribution (χac′) and a peak at the out-of-phase component (χac″), which shifts to higher temperatures with increasing values of f. The Voguel-Fulcher law applied to the χac″ data yielded an activation energy Ea/kB = 21.3 K (40.1 K), the glassy temperature TG = 15.5 K (38.2 K), and a relaxation time τ0=9.1×10−7 s (8.3×10−7 s), for the sample with x = 10 (x = 9). A plot of χac″ vs χac′ for a broad range of T and f yielded a broad maximum near the glassy temperature TG for both sample concentrations.

Electronic effects of ligand substitution on spin crossover in a series of diiminoquinonoid-bridged Fe(II)2 complexes.

A series of four isostructural Fe(II)2 complexes, [(TPyA)2Fe2((X)L)](2+) (TPyA = tris(2-pyridylmethyl)amine; (X)L(2-) = doubly deprotonated form of 3,6-disubstituted-2,5-dianilino-1,4-benzoquinone; X = H, Br, Cl, and F), were synthesized to enable a systematic study of electronic effects on spin crossover behavior. Comparison of X-ray diffraction data for these complexes reveals the sole presence of high-spin Fe(II) at 225 K and mixtures of high-spin and low-spin Fe(II) at 100 K, which is indicative of incomplete spin crossover. In addition, crystal packing diagrams show that these complexes are well-isolated from one another in the solid state, owing primarily to the presence of bulky tetra(aryl)borate counteranions, such that spin crossover is likely not significantly affected by intermolecular interactions. Variable-temperature dc magnetic susceptibility data confirm the structural observations and reveal that 54(1), 56(1), 62(1), and 84(1)% of Fe(II) centers remain high-spin even below 65 K. Moreover, fits to magnetic data provide crossover temperatures of T1/2 = 160(1), 124(1), 121(1), and 110(1) K for X = H, Br, Cl, and F, respectively, along with enthalpies of ΔH = 11.4(3), 8.5(3), 8.3(3), and 7.5(2) kJ/mol, respectively. These parameters decrease with increasing electronegativity of X and thus increasing electron-withdrawing character of (X)L(2-), suggesting that the observed trends originate primarily from inductive effects of X. Moreover, when plotted as a function of the Pauling electronegativity of X, both T1/2 and ΔH undergo a linear decrease. Further analyses of the low-temperature magnetic data and variable-temperature Mössbauer spectroscopy suggest that the incomplete spin crossover behavior in [(TPyA)2Fe2((X)L)](2+) is best described as a transition from purely [FeHS-FeHS] (HS = high-spin) complexes at high temperature to a mixture of [FeHS-FeHS] and [FeHS-FeLS] (LS = low-spin) complexes at low temperature, with the number of [FeHS-FeHS] species increasing with decreasing electron-withdrawing character of (X)L(2-).

Physical properties and magnetic structure of the intermetallicCeCuBi2compound

In this work, we combined magnetization, pressure dependent electrical resistivity, heat-capacity, 63Cu Nuclear Magnetic Resonance (NMR) and X-ray resonant magnetic scattering experiments to investigate the physical properties of the intermetallic CeCuBi2 compound. Our single crystals show an antiferromagnetic ordering at TN ~ 16 K and the magnetic properties indicate that this compound is an Ising antiferromagnet. In particular, the low temperature magnetization data revealed a spin-flop transition at T = 5 K when magnetic fields about 5.5 T are applied along the c-axis. Moreover, the X-ray magnetic diffraction data below TN revealed a commensurate antiferromagnetic structure with propagation wavevector (0 0 1/2) with the Ce^3+ moments oriented along the c-axis. Furthermore, our heat capacity, pressure dependent resistivity and temperature dependent 63Cu NMR data suggest that CeCuBi2 exhibits a weak heavy fermion behavior with strongly localized Ce^3+ 4f electrons. We thus discuss a scenario taking into account the anisotropic magnetic interaction between the Ce^3+ ions along with the tetragonal crystalline electric field effects in CeCuBi2.

A mononuclear transition metal single-molecule magnet in a nuclear spin-free ligand environment.

The high-spin pseudotetrahedral complex [Co(C3S5)2](2-) exhibits slow magnetic relaxation in the absence of an applied dc magnetic field, one of a small number of mononuclear complexes to display this property. Fits to low-temperature magnetization data indicate that this single-molecule magnet possesses a very large and negative axial zero-field splitting and small rhombicity. The presence of single-molecule magnet behavior in a zero-nuclear spin ligand field offers the opportunity to investigate the potential for this molecule to be a qubit, the smallest unit of a quantum information processing (QIP) system. However, simulations of electron paramagnetic resonance (EPR) spectra and the absence of EPR spectra demonstrate that this molecule is unsuitable as a qubit due to the same factors that promote single molecule magnet behavior. We discuss the influence of rhombic and axial zero-field splitting on QIP applications and the implications for future molecular qubit syntheses.

Anomalous specific heat, magnetic, and electrical transport properties around magnetic instability in Ce3−xLaxCo4Sn13

Ce3Co4Sn13 exhibits interesting physical properties including a large increase in the magnetic specific heat, ΔC(T)/T, at low-temperatures with a maximum value of about 4JK−2molCe−1 and a cross-over from heavy fermion behavior with antiferromagnetic correlations at low magnetic field to single impurity Kondo behavior by applying the field larger than ∼3 T. In order to study the expected quantum criticality of Ce3Co4Sn13 we investigated electrical resistivity, magnetoresistivity, magnetic susceptibility and specific heat of Ce3−xLaxCo4Sn13 and showed that partial substitution of Ce by La does not lead to long range magnetic order, and the low-temperature properties are not typical of the quantum critical point (QCP). The magnetoresistivity of Ce3−xLaxCo4Sn13 has a conventional Kondo character. With increasing of the magnetic field resistivity follows power-law behavior over one decade in temperature for the samples with x ≠ 0 of the series, and exponent n in ρ ∼ Tn is strongly field dependent. The low-temperature specific heat of Ce3−xLaxCo4Sn13 exhibits evolution from a magnetically correlated heavy fermion state to a single impurity state at the critical concentration x = xC = 0.6, however, for xC the C(T)/T behavior is not typical for QCP. The low-temperature resistivity and magnetic susceptibility data give evidence for changeover from Kondo lattice to a single-ion Kondo behaviour at xC, when the La content in Ce3−xLaxCo4Sn13 increases.

Magnetic phase diagram of an Ising spin-chain system α-CoV2O6 with 1/3 magnetization plateau

α-CoV2O6 exhibits a linear chain structure with monoclinic system which does not show any ingredient for geometrical frustration. Magnetic properties of α-CoV2O6 are investigated by means of magnetic and heat capacity measurements. 1/3 magnetization plateau occurs at low temperature while magnetic field is applied along the easy c-axis. Magnetic phase diagram (H vs. T) is constructed by low-temperature susceptibility and magnetization data. On the basis of the model of one-spin flip transition for a two-sublattice antiferromagnet, the spin arrangements of antiferromagnetic, ferrimagnetic and ferromagnetic states are also suggested.

Chemical pressure effects on structural, dielectric and magnetic properties of solid solutions Mn3−xCoxTeO6

The effects of Co2+ doping on the structural, magnetic and dielectric properties of the multiferroic frustrated antiferromagnet Mn3TeO6 have been investigated. Ceramic samples of the solid solution series Mn3−xCoxTeO6 were prepared by a solid-state reaction route. X-ray and neutron powder diffraction and electron microscopy techniques were combined with calorimetric, dielectric and magnetic measurements to investigate the dependence of the crystal structure and physical properties on temperature and composition. It is shown that the compounds with x≤2.4 adopt the trigonal corundum-related structure of pure Mn3TeO6 (space group R3¯) in the temperature range 5–295K and that the lattice parameters a and c and the unit-cell volume V decrease linearly with increasing Co2+ concentration. The low-temperature magnetic susceptibility and heat capacity data evidence the antiferromagnetic ordering of all samples. The Neel temperature linearly increases with Co2+ concentration x. Curie–Weiss fits of the high temperature susceptibility indicate that the magnetic frustration decreases with x. The derived magnetic structure of Mn3TeO6 can be described as an incommensurately modulated magnetic spin state with k=[0,0,kz] and an elliptical spin-spiral order of spins within the chains of MnO6 octahedra. With increasing Co2+ concentration the propagation vector kz changes from 0.453 (x=0) to 0.516 (x=2.4). The magnetic anisotropy changes as well, leading to a reorientation of the spiral-basal plane. A possible coexistence of long-range order of electrical dipoles and magnetic moments in Mn3−xCoxTeO6 is discussed.