High-temperature Magnetic Susceptibility Research Articles

First-order magnetostructural transition in single crystals of the honeycomb lattice ruthenate Li2RuO3

Li$_2$RuO$_3$ is known to crystallize in either $C2/m$ or $P2_1/m$ structures at room temperature. We report the first single crystal growth of Li$_2$RuO$_3$ and Na substituted crystals (Li$_{0.95}$Na$_{0.05}$)$_{2}$RuO$_3$ crystallizing in the $P2_1/m$ structure where a magneto-structural transition is observed at high temperatures. Using high temperature ($T \leq 1000$~K) magnetic susceptibility $\chi$ measurements we study the magnetic anisotropy across the magneto-structural transition. Our results show for the first time that for Li$_2$RuO$_3$ the magnetic and structural transitions most likely occur at slightly different temperatures. The structural transition which is first order-like occurs first ($T \approx 570$~K) and drives the magnetic transition ($T \approx 540$~K). Rather surprisingly, just $5\%$ Na substitution for Li affects the magneto-structural transition in an interesting way. The first order transition temperature stays $\approx 540$~K, the magnetic anisotropy is reversed, and the Ru-Ru dimerization pattern changes from two short and four long Ru-Ru bonds per honeycomb in an armchair pattern for Li$_2$RuO$_3$ to four short and two long bonds per honeycomb in (Li$_{0.95}$Na$_{0.05}$)$_{2}$RuO$_3$ which can be viewed as two inter-penetrating armchair patterns.

Slater Insulator in Iridate Perovskites with Strong Spin-Orbit Coupling.

The perovskite SrIrO_{3} is an exotic narrow-band metal owing to a confluence of the strengths of the spin-orbit coupling (SOC) and the electron-electron correlations. It has been proposed that topological and magnetic insulating phases can be achieved by tuning the SOC, Hubbard interactions, and/or lattice symmetry. Here, we report that the substitution of nonmagnetic, isovalent Sn^{4+} for Ir^{4+} in the SrIr_{1-x}Sn_{x}O_{3} perovskites synthesized under high pressure leads to a metal-insulator transition to an antiferromagnetic (AF) phase at T_{N}≥225 K. The continuous change of the cell volume as detected by x-ray diffraction and the λ-shape transition of the specific heat on cooling through T_{N} demonstrate that the metal-insulator transition is of second order. Neutron powder diffraction results indicate that the Sn substitution enlarges an octahedral-site distortion that reduces the SOC relative to the spin-spin exchange interaction and results in the type-G AF spin ordering below T_{N}. Measurement of high-temperature magnetic susceptibility shows the evolution of magnetic coupling in the paramagnetic phase typical of weak itinerant-electron magnetism in the Sn-substituted samples. A reduced structural symmetry in the magnetically ordered phase leads to an electron gap opening at the Brillouin zone boundary below T_{N} in the same way as proposed by Slater.

Synthesis and Characterization of Ba[CoSO]: Magnetic Complexity in the Presence of Chalcogen Ordering.

Barium thio-oxocobaltate(II), Ba[CoS2/2 O2/2 ], was synthesized by the reaction of equimolar amounts of BaO, Co, and S in closed silica ampoules. The title compound (Cmcm, a=3.98808(3), b=12.75518(9), c=6.10697(4) Å) is isostructural to Ba[ZnSO]. The use of soft X-ray absorption spectroscopy confirmed that cobalt is in the oxidation state +2 and tetrahedrally coordinated. Its coordination consists of two sulfur and two oxygen atoms in an ordered fashion. High-temperature magnetic susceptibility data indicate strong low-dimensional spin-spin interactions, which are suggested to be closely related to the layer-type crystal structure and perhaps the ordered distribution of sulfur and oxygen. Antiferromagnetic ordering below TN =222 K is observed as an anomaly in the specific heat, coinciding with a significant lowering of the magnetic susceptibility. Density functional theory calculations within a generalized-gradient approximation (GGA)+U approach identify an antiferromagnetic ground state within the square-like two-dimensional layers of Co, and antiferromagnetic correlations for nearest and next nearest neighbors along bonds mediated by oxygen or sulfur. However, this magnetic state is subject to frustration by relatively strong interlayer couplings.

Cluster spin-glass ground state in quasi-one-dimensionalKCr3As3

We report structural and physical properties of a new quasi-one-dimensional Cr-based compound, KCr$_{3}$As$_{3}$, which is prepared by potassium deintercalation from the superconductive K$_{2}$Cr$_{3}$As$_{3}$. KCr$_{3}$As$_{3}$ adopts the TlFe$_{3}$Te$_{3}$-type structure with space group $P6_{3}$/$m$ (No. 176). The high-temperature magnetic susceptibility obeys the Curie-Weiss law with an effective magnetic moment of 0.68 $\mu_{\mathrm{B}}$/Cr. Below 56 K the susceptibility deviates from the high-temperature Curie-Weiss behavior, coinciding with the rapid increase in resistivity, which suggests formation of spin clusters. The short-range spin correlations are also supported by the specific-heat data. The title material does not exhibit bulk superconductivity; instead, it shows a cluster spin-glass state below $\sim$ 5 K.

Low temperature magnetic properties of the Late Archean Boolgeeda iron formation (Hamersley Group, Western Australia): environmental implications

The origin of the iron oxides in Archean and Paleoproterozoic Banded Iron Formations is still a debated question. We report low and high temperature magnetic properties, susceptibility and saturation magnetization results joined with scanning microscope observations within a 35 meters section of the Late Archean Boolgeeda Iron Formation of the Hamersley Group, Western Australia. With the exception of two volcanoclastic intervals characterized by low susceptibility and magnetization, nearly pure magnetite is identified as the main magnetic carrier in all iron-rich layers including hematite-rich jasper beds. Two populations of magnetically distinct magnetites are reported from a 2 meter-thick interval within the section. Each population shows a specific Verwey transition temperature: one around 120-124 K and the other in the range of 105-110 K. This temperature difference is interpreted to reflect two distinct stoichiometry and likely two episodes of crystallization. The 120-124K transition is attributed to nearly pure stoichiometric magnetite, SEM and microprobe observations suggest that the lower temperature transition is related to chemically impure silician magnetite. Microbial-induced partial substitution of iron by silicon is suggested here. This is supported by an increase in Total Organic Carbon (TOC) in the same interval.

The use of fire at Zhoukoudian: evidence from magnetic susceptibility and color measurements

In order to provide direct evidence for the use of fire by humans at Locality 1, Zhoukoudian, we examine the burnt and unburnt sediments of newly excavated area in Layer 4 by detailed measurements of magnetic susceptibility, color, and diffuse reflectance spectrum. Results show that the magnetic susceptibility and redness of the burnt sediments are remarkably higher than those of other areas on the same level: up to ~22 times for magnetic susceptibility and ~3 times for redness of those of the adjacent unburnt sediments. Fine-grained (superparamagnetic/stable single-domain) magnetite and hematite grains make dominant contributions to the distinctly high values of magnetic susceptibility and redness in the burnt sediments. Diffuse reflectance spectroscopy results show that the burnt sediments contain more hematite than those of other areas and localities 2 and 3. High-temperature magnetic susceptibility measurements demonstrate that the burnt sediments have been heated above 700 °C. Those changes in low-frequency magnetic susceptibility and redness are impossibly resulted from natural fires, thus most likely signaling the human activities of controlled use of fire. However, further work is needed to confirm whether or not these heat-affected sediments were produced in situ.

Partial Spin Ordering and Complex Magnetic Structure in BaYFeO4: A Neutron Diffraction and High Temperature Susceptibility Study

The novel iron-based compound, BaYFeO4, crystallizes in the Pnma space group with two distinct Fe(3+) sites, that are alternately corner-shared [FeO5](7-) square pyramids and [FeO6](9-) octahedra, forming into [Fe4O18](24-) rings, which propagate as columns along the b-axis. A recent report shows two discernible antiferromagnetic (AFM) transitions at 36 and 48 K in the susceptibility, yet heat capacity measurements reveal no magnetic phase transitions at these temperatures. An upturn in the magnetic susceptibility measurements up to 400 K suggests the presence of short-range magnetic behavior at higher temperatures. In this Article, variable-temperature neutron powder diffraction and high-temperature magnetic susceptibility measurements were performed to clarify the magnetic behavior. Neutron powder diffraction confirmed that the two magnetic transitions observed at 36 and 48 K are due to long-range magnetic order. Below 48 K, the magnetic structure was determined as a spin-density wave (SDW) with a propagation vector, k = (0, 0, (1)/3), and the moments along the b-axis, whereas the structure becomes an incommensurate cycloid [k = (0, 0, ∼0.35)] below 36 K with the moments within the bc-plane. However, for both cases the ordered moments on Fe(3+) are only of the order ∼3.0 μB, smaller than the expected values near 4.5 μB, indicating that significant components of the Fe moments remain paramagnetic to the lowest temperature studied, 6 K. Moreover, new high-temperature magnetic susceptibility measurements revealed a peak maximum at ∼550 K indicative of short-range spin correlations. It is postulated that most of the magnetic entropy is thus removed at high temperatures which could explain the absence of heat capacity anomalies at the long-range ordering temperatures. Published spin dimer calculations, which appear to suggest a k = (0, 0, 0) magnetic structure, and allow for neither low dimensionality nor geometric frustration, are inadequate to explain the observed complex magnetic structure.

Investigation of the Temperature Dependence of the Oscillation of the Magnetic Susceptibility in Semiconductors

The temperature dependence of the magnetic susceptibility oscillations semiconductors was considered in a quantizing magnetic field. With the help of mathematical modeling of the thermal broadening of the energy levels, the temperature dependence of the de Haas-van Alphen effect in quantizing magnetic field was investigated. The influence of temperature on the de Haas-van Alphen with the help of free energy of electrons ( ) ( ) , χ HT in semiconductors was determined. Theoretical results of the mathematical simulation were compared with experimental data for bismuth. Using the proposed model of the low-temperature ( ) ( ) , χ HT , high-temperature oscillation magnetic susceptibility in semiconductors was calculated.

The new nickel tellurite chloride compound Ni15Te12O34Cl10– synthesis, crystal structure and magnetic properties

A new nickel tellurite oxohalide, Ni(15)Te(12)O(34)Cl(10), has been prepared by chemical vapour transport reactions and the crystal structure was determined by single-crystal X-ray diffraction. The compound crystallizes in the triclinic space group P1[combining macron] with the pseudomonoclinic cell parameters a = 10.3248(6) Å, b = 10.3249(6) Å, c = 11.6460(8) Å, α = 73.782(6)°, β = 73.782(6)°, γ = 63.51(2)°, Z = 1, R(1) = 0.0264. The Ni(2+) ions have octahedral [NiO(6)] and [NiO(4)Cl(2)] coordinations, the Te(4+) ions have one-sided [TeO(3)] and [TeO(4)] coordinations. The crystal structure can be described as consisting of nickel oxide ribbons extending along (001) that are connected by corner sharing [TeO(3)] and [TeO(4)] groups to build the open framework structure. The chlorine atoms and the Te-lone pairs are facing voids in the oxide framework. The new compound undergoes two successive antiferromagnetic ordering transitions at ∼50 K and ∼10 K. The Curie-Weiss temperature obtained from detailed evaluation of the high-temperature magnetic susceptibilities is positive indicating predominant ferromagnetic superexchange interactions between the Ni magnetic moments.

Spin and charge states of Co in half-doped layered cobaltates La1.5Ca0.5CoO4and La1.5Sr0.5CoO4

We have investigated the charge dynamics and local spin state in half-doped layered cobaltates La${}_{1.5}$Ca${}_{0.5}$CoO${}_{4}$ and La${}_{1.5}$Sr${}_{0.5}$CoO${}_{4}$. By examining temperature-dependent infrared-active phonon modes, we found clear signatures of the structural distortion related to the spin-state transition around ${T}_{S}=400--600$ K. While the kinetic energy of the electronic system, estimated by the low-energy spectral weight in the optical conductivity spectrum, as well as the optical gap energy is strongly affected by the charge-order instability, it shows a noticeable enhancement upon the spin-state transition which is attributed to the release of the spin blockade of the electron hopping between the low-spin (Co${}^{3+}$) and high-spin (Co${}^{2+}$) states. These understandings of the spin state are further evidenced by the reexamination of high-temperature Seebeck coefficient and magnetic susceptibility.

High-resolution x-ray scattering studies of structural phase transitions in Ba(Fe1−xCrx)2As2

We have performed high resolution x-ray scattering measurements on single crystal samples of Ba(Fe(1-x)Cr(x))2As2 (x = 0 to 0.335). These measurements examine the effect of Cr-doping on the high temperature tetragonal (I4/mmm) to low temperature orthorhombic (Fmmm) structural phase transition of the parent compound BaFe2As2. Increasing Cr concentration is found to suppress the structural transition temperature (Ts), and reduce the magnitude of the orthorhombic strain (delta). The doping dependence of the orthorhombic strain, combined with complementary measurements of the high temperature magnetic susceptibility, suggests the presence of a magnetostructural crossover at x ~ 0.05. In particular, this crossover appears to mark a shift from strong to weak orthorhombicity and from predominantly itinerant to localized magnetic behavior.

Dynamic effects of dipolar interactions on the magnetic behavior of magnetite nanoparticles

Isothermal magnetization and initial dc susceptibility of spheroidal, nearly monodisperse magnetite nanoparticles (typical diameter: 8 nm) prepared by a standard thermo-chemical route have been measured between 10 and 300 K. The samples contained magnetite nanoparticles in the form of either a dried powder (each nanoparticle being surrounded by a stable oleic acid shell as a result of the preparation procedure) or a solid dispersion in PEGDA-600 polymer; different nanoparticle (NP) concentrations in the polymer were studied. In all samples the NPs were not tightly agglomerated nor their ferromagnetic cores were directly touching. The high-temperature inverse magnetic susceptibility is always found to follow a linear law as a function of T, crossing the horizontal axis at negative temperatures ranging from 175 to about 1,000 K. The deviation from the standard superparamagnetic behavior is related to dipolar interaction among NPs; however, a careful analysis makes it hard to conclude that such a behavior originates from a dominant antiferromagnetic character of the interaction. The results are well explained considering that the studied samples are in the interacting superparamagnetic (ISP) regime. The ISP model is basically a mean field theory which allows one to straightforwardly account for the role of magnetic dipolar interaction in a NP system. The model predicts the existence of specific scaling laws for the reduced magnetization which have been confirmed in all studied samples. The interaction of each magnetic dipole moment with the local, random dipolar field produced by the other dipoles results in the presence of a large fluctuating energy term whose magnitude is comparable to the static barrier for magnetization reversal/rotation related to magnetic anisotropy. On the basis of the existing theories on thermal crossing of a barrier whose height randomly fluctuates in time it is predicted that the rate of barrier crossing is substantially driven by the rate of barrier fluctuations, which is fast (108–109 Hz) and almost independent of temperature. As a consequence, the standard picture of superparamagnetic NPs which undergo single-particle blocking by a static barrier below the blocking temperature should be substantially revised, at least in the present materials. The ISP model is perfectly matching with the view of activated magnetization rotation whose kinetics is significantly modified by barrier height fluctuations.

Anomalous Spin Dynamics Observed by High-Frequency ESR in Honeycomb Lattice Antiferromagnet InCu2/3V1/3O3

High-frequency ESR results on the S=1/2 Heisenberg hexagonal antiferromagnet InCu2/3V1/3O3 are reported. This compound appears to be a rare model substance for the honeycomb lattice antiferromagnet with very weak interlayer couplings. The high-temperature magnetic susceptibility can be interpreted by the S=1/2 honeycomb lattice antiferromagnet, and it shows a magnetic-order-like anomaly at TN=38 K. Although, the resonance field of our high-frequency ESR shows the typical behavior of the antiferromagnetic resonance, the linewidth of our high-frequency ESR continues to increase below TN, while it tends to decrease as the temperature in a conventional three-dimensional antiferromagnet decreases. In general, a honeycomb lattice antiferromagnet is expected to show a simple antiferromagnetic order similar to that of a square lattice antiferromagnet theoretically because both antiferromagnets are bipartite lattices. However, we suggest that the observed anomalous spin dynamics below TN is the peculiar feature of the honeycomb lattice antiferromagnet that is not observed in the square lattice antiferromagnet.

Synthesis, structural and magnetic properties of nanostructured Ca0.9Gd0.1MnO3 obtained by modified glycine nitrate procedure (MGNP)

Ca0.9Gd0.1MnO3 nanopowders with perovskite type crystal structure were synthesized by modified glycine nitrate procedure. Nanopowders were prepared by combining glycine with metal nitrates and/or metal acetates in their appropriate stoichiometric ratios. Modification of the procedure was performed by partial replacement of nitrates by acetates, in order to control the burn-up reaction. Obtained Ca0.9Gd0.1MnO3 powders were calcinated in the temperature interval from 850°C to 950°C for 10min. Properties such as phase evolution, lattice parameters, chemical composition and magnetic properties were monitored by DTA, X-ray diffraction, SEM/EDS and magnetic measurements. Magnetic measurements performed at the sample with the smallest crystallite size showed that a 10% of Gd3+ substituted Ca2+ ions changes antiferromagnetic properties of CaMnO3 by the introduction of ferromagnetic interaction due to a double exchange between Mn3+ and Mn4+ ions. Presence of competing interactions and their randomness lead to a formation of a spin glass state below Neel temperature TN=110K. From the high temperature magnetic susceptibility measurements effective magnetic moment of manganese ions is determined which lies between the values for Mn3+ and Mn4+ ions.

Regulating low-dimensional magnetic behavior of organic radicals in crystalline hydrogen-bonded host frameworks

A series of S = ½ organic radicals—TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl), 4-methoxy-TEMPO, and 4-oxo-TEMPO—have been included in the cavities of porous lamellar host frameworks constructed from guanidinium (G) cations and organodisulfonate (DS) anions, which assemble into hydrogen-bonded guanidinium sulfonate (GS) sheets connected by organodisulfonate pillars that create cavities between the sheets. The pillars can project above or below the GS sheet in different configurations, affording various architectural framework isomers whose selectivity is determined by the relative sizes of the guests and the pillars. Each framework isomer is endowed with uniquely sized and shaped cavities, which influence the molecular arrangement of the radical guests included within the host lattice. Notably, TEMPO guests in the 1-D channels of simple brick G22BPDShost (BPDS = biphenyl-4,4′-disulfonate) arrange as a two-leg ladder (a chain of dimers), whereas TEMPO guests in the cavities of zigzag brick G22NDShost (NDS = naphthalene-2,6-disulfonate) form dimers that are distributed into a 2-D square-planar lattice. The high-temperature magnetic susceptibility, χmol, conformed with Curie–Weiss behavior, with negative Weiss constants, consistent with bulk antiferromagnetic ordering. The Neel temperatures (TN) for G22BPDS·2(TEMPO) and G22NDS·2(TEMPO) were found to be 3.83 K and 4.10 K, respectively, as indicated by the presence of a broad maximum in χmol near these temperatures. In contrast, TN for host-free crystalline TEMPO is lower at 2.3 K, suggesting that enforced ordering can alter the magnetic properties of the TEMPO guests. The low-temperature χmol data for G22BPDS·2(TEMPO) agreed well with the Troyer two-leg ladder spin model, with J/kB = −7.29 K along the rungs of the ladder (intra-dimer) and J/kB = −0.45 K along the legs of the ladder (inter-dimer). The χmol data for G22NDS·2(TEMPO) agreed best with Bleaney–Bowers behavior for isolated dimers with J/kB = −3.31 K for the encapsulated TEMPO dimer. These results demonstrate that magnetic behavior, including dimensionality, can be manipulated through judicious selection of host and magnetic guests.

Crystal structure and physical properties of NpRh2Sn, a new Np-based ternary compound

We report on the synthesis and physical characterization of a new compound, NpRh2Sn, prepared by arc-melting under argon atmosphere. Rietveld analysis of the powder x-ray diffraction pattern reveals an orthorhombic, Fe3C-type structure, with lattice parameters that are the shortest among the AnT2Sn series (An = U, Np, Pu, and T = Pd, Rh). A fit of the high-temperature magnetic susceptibility curve, χ(T), gives a Curie-Weiss temperature ΘCW = −29K, and an effective magnetic moment μeff = 2.42μB. The stabilization of the CW r eff r B antiferromagnetic order below TN = 34 K is revealed by a cusp in χ(T) and by a small anomaly in the specific heat curve, CP(T). An enhanced value of the Sommerfeld coefficient, γ ≈ 107 mJ mol−1 K−2, indicates a moderate heavy-fermion state. NpRh2Sn is the first member of the AnRh2Sn family, and a rare representative of heavy-fermion systems amidst Np- intermetallics.

Magnetic properties of Mn-oxide nanoparticles dispersed in an amorphous SiO2 matrix

Samples of Mn-oxide nanoparticles dispersed in an amorphous SiO2 matrix with manganese concentration 0.7 and 3at% have been synthesized by a sol–gel method. Transmission electron microscopy analysis has shown that the samples contain agglomerates of amorphous silica particles 10–20nm in size. In silica matrix two types of Mn-rich particles are dispersed, smaller nanoparticles with dimensions between 3 and 10nm, and larger crystalline areas consisting of aggregates of the smaller nanoparticles. High-temperature magnetic susceptibility study reveals that dominant magnetic phase at higher temperatures is λ-MnO2. At temperatures below TC=43K strong ferrimagnetism originating from the minor Mn3O4 phase masks the relatively weak magnetism of λ-MnO2 with antiferromagnetic interactions. Magnetic field dependence of the maximum in the zero-field-cooled magnetization for both the samples in the vicinity of 40K, and a frequency shift of the real component of the ac magnetic susceptibility in the sample with 3at% Mn suggest that the magnetic moments of the smaller Mn3O4 nanoparticles with dimensions below 10nm are exposed to thermally activated blocking process just below the Curie temperature TC. Appearance of a maximum in the zero-field-cooled magnetization for both the samples below 10K indicates possible spin glass freezing of the magnetic moments at low temperatures which might occur in the geometrically frustrated Mn sublattice of the λ-MnO2 crystal structure.

Diagenetic control of magnetic susceptibility variation in Core MD98-2172 from the Eastern Timor Sea

Detailed mineral magnetic measurements, integrated with grain-size distribution and X-ray diffraction (XRD) analyses, were made on the marine sediments of Core MD98-2172, retrieved from the Eastern Timor Sea. Values of magnetic susceptibility in this core drop sharply down-core from ∼3.85 m deep below sediment/water interface and are very low at ∼5.35 m. However, both XRD and grain-size distribution results show no sudden change in terrigenous input during sedimentation. Mineral magnetic results indicate that the depth of ∼3.85 m may be an oxic/anoxic boundary. Therefore, the sediments below ∼3.85 m have been subjected to intense reductive diagenesis, whereas the sediments above ∼3.85 m are seldom affected. The magnetic properties of the sediments shallower than 3.85 m are dominated by pseudo-single domain (PSD) magnetite, with little down-core variation in its content and grain size. Below ∼3.85 m, the magnetic mineral assemblages that have survived in the sediments may record different stages of the reductive diagenesis: (1) the sediments from the 3.85–5.35 m interval are at the stage of iron oxide reduction; PSD magnetite is the major magnetic contributor, but it becomes less abundant and coarser down-core; (2) the sediments below ∼5.35 m are at the stage of sulphate reduction; ferrimagnetic minerals almost vanish and paramagnetic minerals contribute to down-core susceptibility variations, including pyrite as evidenced by high-temperature magnetic susceptibility measurements. However, the susceptibility variations below ∼5.35 m of Core MD98-2172 show obvious periodicity, despite the intense effect of reductive diagenesis. Furthermore, the down-core susceptibility variations are coincident with fluctuations in the quantity of fine detrital particles (<8 μm), which may come mainly from the advection of the Indonesia Throughflow (ITF) and/or river input from Timor. Therefore, for Core MD98-2172, susceptibility variation below ∼5.35 m, which potentially correspond to fluctuations in the quantity of fine particles, may record the histories of the development of the ITF and precipitation on Timor.

ChemInform Abstract: Structure and Ferromagnetism of the Rare-Earth Zintl Compounds: Yb14MnSb11 and Yb14MnBi11.

Rare-earth transition metal compounds Yb14MnSb11 and Yb14MnBi11 have been prepared by heating stoichiometric amounts of the elements at 1000−1200 °C. These compounds are isostructural with the Zintl compound Ca14AlSb11 and crystallize in the tetragonal space group I41/acd (Z = 8). Single-crystal X-ray data (143 K) were refined for Yb14MnSb11 [a = 16.615(2) A, c = 21.948(4) A, V = 6059(2) A3, and R1/wR2 (0.0299/0.0479)] and Yb14MnBi11 [a = 17.000(3) A, c = 22.259(6) A, V = 6433(2) A3, R1/wR2 (0.0631/0.133)]. Structural analysis is consistent with Yb2+. Temperature-dependent magnetic susceptibility data show that Yb14MnSb11 orders ferromagnetically at 56 K and Yb14MnBi11 has a ferromagnetic transition at 58 K and another transition at 28 K. High-temperature magnetic susceptibility data can be fit with a modified Curie−Weiss law and give μeff = 4.92(2)μB and μeff = 4.9(1)μB for the Sb and Bi compounds, respectively. This result is consistent with the assignment of Mn3+ (d4) and Yb2+ (f 14). Single-crystal ma...

Absence of magnetic ordering in low dimensional mixed magnetic Mn 1− xNi xCl 2·H 2O

A new mixed magnet, Mn 1− x Ni x Cl 2·H 2O, is examined by dc magnetization and susceptibility measurements across the entire composition range. The pure components are quasi-one-dimensional Heisenberg antiferromagnets ordering at 2.17 K (Mn) and 5.6 5 K (Ni) due to weaker interchain exchange supplementing the dominant exchange along MCl 2MCl 2M… chemical and structural chains. High temperature magnetic susceptibilities yield Curie and Weiss constants in χ M= C/( T− θ). C( x) is linear but θ( x) displays curvature, which is analyzed to show that unlike-ion exchange is ferromagnetic and similar in size to like-ion. Most notable is the absence of antiferromagnetic susceptibility maxima down to 1.6 K from x=0.10 to 0.95. For x=0.05 a susceptibility maximum appears, with T max almost 20% lower than in the pure Mn component but T c reduced by 2%. The size of the susceptibility is enhanced by admixture, the effect of disrupted antiferromagnetic tendencies. Magnetization isotherms evolve with composition. Larger values of magnetization, under the same measuring conditions, occur for mixtures than for pure components, consistent with frustration, which weakens antiferromagnetic alignment tendencies. The competing ferromagnetic (Ni) and antiferromagnetic (Mn) intrachain interactions, along with disorder and low dimensional characteristics, presumably lead to the absence of magnetic order over a remarkably broad composition range.