High-temperature Magnetic Susceptibility Research Articles

Interpreting high-temperature magnetic susceptibility data of natural systems

High-temperature susceptibility (HT-χ) data are routinely measured in Earth, planetary, and environmental sciences to rapidly identify the magnetic mineralogy of natural systems. The interpretation of such data can be complicated. Whilst some minerals are relatively unaltered by heating and are easy to identify through their Curie or Néel temperature, other common magnetic phases, e.g., iron sulphides, are very unstable to heating. This makes HT-χinterpretation challenging, especially in multi-mineralogical samples. Here, we report a review of the HT-χdata measured primarily at Imperial College London of common magnetic minerals found in natural samples. We show examples of “near pure” natural samples, in addition to examples of interpretation of multi-phase HT-χdata. We hope that this paper will act be the first reference paper for HT-χdata interpretation.

Exchange interaction for Mn acceptors in GaAs: Revealing its strong deformation dependence

In this paper we calculate exchange interaction constant between manganese ion inner electronic $d$-shell and GaAs valence band bounded hole using their microscopic multiparticle wave functions. We reveal its parametric dependence on crystal lattice deformations and find out that it could be about and even more than dozens percent when the strain tensor reaches values of $10^{-3} \div 10^{-2}$. This fact is in accordance with the previous hypothesis of deformation dependence of Mn acceptors in GaAs fine energy structure obtained from Raman spectroscopy, and we show that this dependence has the same magnitude. Also, we resolve here the problem of a substantial high temperature mismatch between well-developed theory and experimental data for the static magnetic susceptibility of Mn ions in GaAs. We show by numerical estimates and calculations that quite a strong parametric dependence of the exchange coupling value on GaAs lattice expansion determines the high temperature (above $50~$K) magnetic susceptibility reduction as well.

Two new cubic perovskite oxides Ba3CoSb2O9 and Ba2SrCoSb2O9: Syntheses, crystal structures and magnetic properties

Two new cubic perovskite oxides Ba3CoSb2O9 and Ba2SrCoSb2O9 were prepared and characterized. Ba3CoSb2O9 was prepared in polycrystalline form by high-pressure (HP) high-temperature treatment of the hexagonal 6H polytype of Ba3CoSb2O9. Polycrystalline samples of Ba2SrCoSb2O9 were obtained at ambient pressure by a solid-state reaction method. Combined Rietveld refinements of X-ray and neutron diffraction patterns indicated that HP Ba3CoSb2O9 and Ba2SrCoSb2O9 both crystallize in a Fm3¯m cubic double perovskite A2BB’O6 structure with formulae Ba2(Sb0.83Co0.17)(Co0.5Sb0.5)O6 and (Ba1.33Sr0.67)Sb(Co0.7Sb0.3)O6, respectively. Electron diffraction results obtained for Ba2SrCoSb2O9 showed no sign of additional periodicity. Weiss temperatures extracted from high-temperature magnetic susceptibility data were θ ​≈ ​−113 ​K and −118 ​K for HP Ba3CoSb2O9 and Ba2SrCoSb2O9, respectively. HP Ba3CoSb2O9 displays a weak ZFC-FC magnetic irreversibilty below 8 ​K. Ba2SrCoSb2O9 exhibits a spin freezing at Tf ​≈ ​6 ​K, and μSR and 121Sb NMR data revealed a magnetic transition towards a disordered ground state.

Itinerant antiferromagnetism in Co3S4−δ

We present experimental and theoretical investigations for the cobalt thiospinel ${\mathrm{Co}}_{3}{\mathrm{S}}_{4\ensuremath{-}\ensuremath{\delta}}$. High-quality samples of ${\mathrm{Co}}_{3}{\mathrm{S}}_{4\ensuremath{-}\ensuremath{\delta}}$ $(\ensuremath{\delta}\ensuremath{\sim}0.1)$ were prepared so as to measure their intrinsic properties. The measurements of magnetic susceptibility, specific heat, and electrical transport consistently indicate an antiferromagnetic transition at $\ensuremath{\sim}60$ K, which is attributed to long-range magnetic ordering in the $\mathrm{Co}(A)$ ($A$-site Co ions) diamond sublattice. In addition, there exists a short-range magnetic ordering at around 120 K associated with the magnetic frustrations. The high-temperature magnetic susceptibility obeys Curie-Weiss law, from which a small effective magnetic moment of $1.0\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ per formula unit is yielded. The main experimental results can be interpreted by the density-functional-theory calculations with a Hubbard $U$ correction of $\ensuremath{\sim}0.5$ eV. Combining the experimental measurements with the theoretical calculations, we conclude that ${\mathrm{Co}}_{3}{\mathrm{S}}_{4}$ represents a rare example of itinerant-electron diamond-lattice antiferromagnet with moderate electron correlations.

High-temperature magnetic susceptibility in metal-electron systems

High-temperature magnetic susceptibility is studied using the Hubbard model. The equation in the high-temperature limit is derived from the Kubo formula as the Curie law of Ns free 1/2-spins, where Ns is the average number of electrons not forming singlets. Exact results for Ns are presented for various cases and are shown to depend only on the total number of electrons Ne and available orbital states, which is the number of lattices L in the single-band case. The condition of kBT≫U, W with the onsite repulsion U and bandwidth W gives Ns=Lp(2−p)/2 with filling p=Ne/L. The numerical calculation for U=0 shows that the universal Curie law holds at temperatures above the threshold temperature T0, compatible with the Fermi temperature. The threshold temperature for U>0 is found to be lower than T0. The application of the present results to a heavy-fermion system near the Mott transition is proposed.

SmI3:4f5 honeycomb magnet with spin-orbital entangled Γ7 Kramers doublet

We report magnetic properties of a 4f-honeycomb iodide SmI3 made up of edge-shared network of SmI6 octahedra. High temperature magnetic susceptibility indicates {\Gamma}7 Kramers doublet ground state of Sm3+ (4f5) ions stabilized by the spin-orbit coupling and octahedral crystal electric field, which interact with Sm-I-Sm bond angle nearly 90 degree. Magnetization measurements down to 0.1 K detected antiferromagnetic correlations and an anomaly in the magnetization curve before saturation without a sign of long-range order. Relevance between SmI3 and the antiferromagnetic Kitaev material proposed in the 4f-electron system is discussed.

Magnetic constitution of topologically trivial thermoelectric PbTe:Cr

In this paper we report on detailed temperature and magnetic field dependence of magnetization of IV-VI semiconductor PbTe doped with mixed valence transition metal Cr2+/3+. The material is studied solely by a SQUID magnetometer in order to quantitatively determine the contribution of single substitutional Cr2+/3+ as well as of various Cr-Te magnetic nanocrystals, including their identification. The applied experimental procedure reveals the presence of about 1019 cm−3 paramagnetic Cr ions, of which 2/3 are the Cr3+ ions formed via self-ionization of Cr2+ resonant donors. These are known to improve the thermoelectric figure of merit parameter zT of this semiconductor. The magnetic finding agrees with previous Hall effect studies thus providing a new experimental support for the proposed electronic structure model of PbTe:Cr system with resonant Cr2+/3+ state located (at low temperatures) about 100 meV above the bottom of the conduction band. Below room temperature a ferromagnetic-like signal points to the presence of Cr-rich nanocrystalline precipitates. Two most likely candidates, namely: Cr2Te3 and Cr5Te8 are identified upon dedicated temperature cycling of the sample at the remnant state. As an ensemble, the nanocrystals exhibit (blocked) superparamagnetic properties. The magnetic susceptibility of both n- and p-type PbTe in the temperature range 100<T<400 K has been established. These magnitudes are essential to properly account for the high temperature magnetic susceptibility of PbTe:Cr.

Frustrated magnetism of the triangular-lattice antiferromagnets α-CrOOH and α-CrOOD

We report a comprehensive investigation of the frustrated magnetism on the delafossite oxides, α-CrOOH and α-CrOOD, which experimentally realize the S = 3/2 nearly-Heisenberg antiferromagnetic (J 1 > 0) model on a triangular lattice with weak single-ion anisotropy (D). The electron spin resonance (ESR), neutron scattering, and specific heat (C m) measurements on both α-CrOOH and α-CrOOD consistently indicate that the long-range 120° Néel order is significantly suppressed and both systems are in the vicinity of a spin-liquid phase with C m ∼ T 2 at low temperatures. The strength of D is quantitatively determined from fitting the high-temperature ESR linewidth and magnetic susceptibility, and its minus sign (D < 0, easy-axis type) is suggested by the low-energy (E ⩽ 2 meV) spin excitations. This easy-axis anisotropy (D/J 1 ∼ −5%) competes with the 120° Néel order and thus enhances the quantum spin fluctuations at low temperatures.

Neutron Diffraction Magnetic and Mossbauer Spectroscopic Studies of Pb0.8Bi0.2Fe0.728W0.264O3 and Pb0.7Bi0.3Fe0.762W0.231O3 Ceramics

We report on high-temperature crystallographic structure, magnetic and physical properties of chemically B-site disordered lead-bismuth iron tungstate, (PFW)1−x(BFO)x (which can be written as Pb0.8Bi0.2Fe0.728W0.264O3 (0.8PFW–0.2BFO) for x = 0.2 and Pb0.7Bi0.3Fe0.762W0.231O3 (0.7PFW–0.3BFO) for x = 0.3) or PBFW), solid solutions through neutron diffraction (ND), magnetization, electron paramagnetic resonance, and Mössbauer spectroscopic studies. From the high temperature magnetic susceptibility measurement, it is observed that increase antiferromagnetic to paramagnetic phase transition around TN = 435 K (Pb0.8Bi0.2Fe0.728W0.264O3) and 504 K (Pb0.7Bi0.3Fe0.762W0.231O3), compared to pure PFW. Room-temperature crystallographic study confirms the formation of pseudo cubic structure with Pm-3m space group, whereas the magnetic structure is commensurate G-type antiferromagnetic ordering. The obtained temperature dependent structural parameters from the ND, evidenced to existence of strong spin-lattice coupling around TN for both the compounds. The discontinuity in the Pb/Bi–O bond length around ferroelectric transition (TC) indicates the presence of magnetoelectric coupling. Interestingly, microscopic 1:1 B-site ordered nanoclusters of PBFW exhibits the ferrimagnetic clusters along with antiferromagnetic order and it observed through the opening of M vs H hysteresis curves in the lower field regime. The EPR and Mössbauer spectroscopic studies well support the magnetic property and also reveal the Fe+3 state, and the weak signal in EPR and broader linewidth in the Mössbauer spectra exhibit the B-site disorderliness.

A new weathering indicator from high-temperature magnetic susceptibility measurements in an Argon atmosphere

SUMMARY Environmental magnetism has become more and more popular because it is inexpensive, rapid and non-destructive. However, the environmental implication of traditional magnetic parameters is changed as the weathering intensity is contrasting. For example, magnetic susceptibility cannot be used as pedogenic index for strongly weathered red soils. Thermal magnetic measurement is a common way to identify magnetic minerals in rocks and sediments. Susceptibility enhancement after a 700 °C heating cycle in an argon atmosphere usually happened for various rocks and sediments. The increase is caused by formation of new magnetite from iron derived from paramagnetic iron-containing minerals. This is similar to pedogenesis or weathering process. The heating process in lab released the residual iron in weatherable iron-containing silicates which has not yet been depleted by contemporary pedogenesis or weathering. This residual iron can be quantified by the amount of susceptibility increase after a heating cycle. A negative correlation between the susceptibility increase after heating and the weathering intensity has been found in high-temperature magnetic susceptibility measurements of several sequences located in different climate zones. Results suggest that the degree of weathering can be estimated for intensely weathered red soils as well as for scarcely weathered loess using the amount of susceptibility change after a 700 °C heating cycle. This study provides new perspectives for developing new weathering and pedoclimate proxies using environmental magnetism.

Crystal structure and magnetic properties of bis-[butyl-tris-(1H-pyrazol-1-yl)borato]iron(II).

The asymmetric unit of the title compound, [Fe(C13H18BN6)2], contains two half independent complex mol-ecules. In each complex, the FeII atom is located on an inversion center and is surrounded by two scorpionate ligand butyl-tris-(1H-pyrazol-1-yl)borate mol-ecules that coordinate to the iron(II) ion through the N atoms of the pyrazole groups. The two independent complex mol-ecules differ essentially in the conformation of the butyl substituents. In the crystal, the complex mol-ecules are linked by a series of C-H⋯π inter-actions, which generate a supra-molecular three-dimensional structure. At 120 K, the average Fe-N bond distance is 1.969 Å, indicating the low-spin state of the iron(II) atom, which does not change upon heating, as demonstrated by high-temperature magnetic susceptibility measurements.

Composition dependence of magnetic properties in the mixed magnet Co1−xNixCl2·H2O

Abstract Effects of disorder, frustration and low dimensional character occur in mixed magnetic Co1−xNixCl2·H2O, examined by dc magnetization and susceptibility measurements across the composition range. The pure components are quasi-one-dimensional antiferromagnets ordering at 15.0 K (Co) and 5.65 K (Ni), with susceptibility maxima at 16.2 and 8.4 K respectively; a spin glass transition also appears in the cobalt system near 8 K. In each compound weaker antiferromagnetic interchain exchange interactions supplement dominant ferromagnetic exchange along MCl2MCl2M… chemical and structural chains. High temperature magnetic susceptibilities are analyzed to yield Curie and Weiss constants in χM = C/(T − θ). Regular but not mean-field composition dependences appear for C and θ. The former is not linear and the latter displays a minimum near x = 0.30. Notable is a susceptibility maxima varying in location only weakly from x = 0.10 to x = 0.70, decreasing markedly only for higher x. Magnetization isotherms evolve regularly as x varies, with systematic composition dependences of a metamagnetic transition field and hysteresis through x = 0.70. A qualitative change in the isotherms occurs for x = 0.90, but substantial curvature still appears with smaller but definite hysteresis. A thermoremanent magnetization is seen in all mixtures, and is largest for the composition extremes. Thus, nonequilibrium magnetic behavior characteristic of the cobalt component, in contrast to the more conventional nickel component, occurs even when the latter is present in strong majority.

Electronic structure of diluted SrFexTi1-xO3-δ solid solutions

The study of diluted solid solutions SrFexTi1-xO3-δ (0.01 < x < 0.10). High-temperature X-ray powder diffraction (HTXRD), Mössbauer spectra and magnetic susceptibility measurements proved that up to x = 0.015 in the solid solutions there are clusters of Fe(III) atoms, which take part in ferromagnetic exchange through oxygen vacancy starting from 200 K via F-centers and a small fraction of single Fe(IV) atoms. An increase in iron content results in the larger clusters with ferromagnetic exchange both between Fe(III)-[O]-Fe(III) and Fe(III)-O-Fe(IV). The solid solutions are mixed electron-hole-ionic conductors and may be used as sensors of the humidity of gases.

Effect of Zn doping on the antiferromagnetism in kagomeCu4−xZnx(OH)6FBr

Barlowite Cu$_4$(OH)$_6$FBr shows three-dimensional (3D) long-range antiferromagnetism, which is fully suppressed in Cu$_3$Zn(OH)$_6$FBr with a kagome quantum spin liquid ground state. Here we report systematic studies on the evolution of magnetism in the Cu$_{4-x}$Zn$_x$(OH)$_{6}$FBr system as a function of $x$ to bridge the two limits of Cu$_4$(OH)$_6$FBr ($x$=0) and Cu$_3$Zn(OH)$_6$FBr ($x$=1). Neutron-diffraction measurements reveal a hexagonal-to-orthorhombic structural change with decreasing temperature in the $x$ = 0 sample. While confirming the 3D antiferromagnetic nature of low-temperature magnetism, the magnetic moments on some Cu$^{2+}$ sites on the kagome planes are found to be vanishingly small, suggesting strong frustration already exists in barlowite. Substitution of interlayer Cu$^{2+}$ with Zn$^{2+}$ with gradually increasing $x$ completely suppresses the bulk magnetic order at around $x$ = 0.4, but leaves a local secondary magnetic order up to $x\sim 0.8$ with a slight decrease in its transition temperature. The high-temperature magnetic susceptibility and specific heat measurements further suggest that the intrinsic magnetic properties of kagome spin liquid planes may already appear from $x>0.3$ samples. Our results reveal that the Cu$_{4-x}$Zn$_x$(OH)$_6$FBr may be the long-thought experimental playground for the systematic investigations of the quantum phase transition from a long-range antiferromagnet to a topologically ordered quantum spin liquid.

Palaeo- and rock magnetic investigations of Late Quaternary sediments from the Upper Congo deep-sea fan: on the difficulty in obtaining palaeomagnetic secular variation records from low latitudes

We report here on results of palaeo- and rock magnetic investigations of two sediment cores from the Upper Congo deep-sea fan. The sediments have a high organic content and contain a heterogeneous Fe-mineral assemblage with biogenic magnetite and detrital (Ti-)magnetite as the main magnetic carrier minerals. Pyrite, hematite, and Fe-oxyhydroxides were identified by comparing high-temperature magnetic susceptibility curves with those from Fe-minerals of known composition. According to AMS 14C dates, the 6.8 m-long profile spans the last 37 kyr. Sediments older than 20 ka are affected by reductive diagenesis that has led to a loss of the fine-grained magnetic mineral fraction. Sediments younger than 20 ka have stable magnetizations. Characteristic remanent magnetization records of inclination and declination were obtained for each core. There is a little agreement between these records, modelled curves, and other sediment records from Equatorial Africa, so no composite record could be established. The cores are not ideal relative palaeointensity recorders and estimates using different normalizers did not yield consistent signals from both cores. Normalization methods used for relative palaeointensity estimation were not developed for sediments that contain large amounts of ultra-fine-grained biogenic magnetite; therefore, the relative palaeointensity estimates should be considered with caution. However, in view of the incoherent picture given by the scarce available palaeointensity information from the region off South-West Africa, the GeoB6517-2 record may provide a tentative relative palaeointensity record for comparison, at least for the past 10 kyr.

Weak ferromagnetism of (Fe1-xNix)Si with B20 structure

Magnetic and electrical properties of Ni doped (Fe1-xNix)Si (x=0-0.5) have been studied by measuring magnetization, magnetic susceptibility and electrical resistivity. FeSi compound (x = 0) shows a weak ferromagnetic property at 2.0 K with small magnetization about 0.07 μB/f.u. at 50 kOe; high temperature magnetic susceptibility suggests paramagnetic property. By the substitution of Fe by Ni, low temperature weak ferromagnetic state is suppressed; magnetization continuously decreases with increasing x up to 0.5. Magnetic susceptibility shows Curie type temperature variation at low temperature; paramagnetic susceptibility does not obey the Curie-Weiss law for all samples. The electrical resistivity of (Fe1-xNix)Si indicates a semiconductive property at x = 0. The low temperature resistivity is substantially suppressed with increasing x; semimetallic and metallic property appears at x = 0.2 and 0.4, respectively.

Structural and physical characterization of NpPt2In7

A new neptunium intermetallic compound, NpPt2In7, has been synthesized in polycrystalline form and characterized by several macroscopic techniques. A Rietveld analysis of its powder X-ray diffraction pattern shows that NpPt2In7 crystallizes in a tetragonal lattice with I4/mmm symmetry and lattice parameters a=4.58471(3) Å, c=21.5065(3) Å. Magnetic susceptibility, electrical resistivity, Hall effect, and heat capacity measurements indicate a metallic character and the occurrence of antiferromagnetic order below a Néel temperature TN = 23 K. The transition is exceptionally robust and TN decreases by 0.2 K under a magnetic field of 9 T. A modified Curie-Weiss fit of the high-temperature magnetic susceptibility curve χ(T) gives an effective magnetic moment μeff=2.54μB close to the value expected for trivalent Np. Low temperature heat capacity measurements give a reduced Sommerfeld linear coefficient close to 25 mJ mol−1K−2 and a Debye Temperature ΘD = 181 K. First principles, correlated-band electronic structure calculations suggest that the neptunium magnetic moment in NpPt2In7 is localized and that a quasi-two-dimensional antiferromagnetic structure could result from the competition of very weak interlayer interactions leading to very anisotropic properties.

DYNAMIC EFFECTS OF DIPOLAR INTERACTIONS ON THE SPECIFIC LOSS POWER OF Mn0.7Zn0.3Fe2O4

In this work, isothermal magnetization and initial dc susceptibility of spheroidal, nearly monodisperse Mn0.7Zn0.3Fe2O4 nanoparticles (typical diameter: 20 nm) prepared by a hydrothermal route have been measured between 10 and 300 K. The high-temperature inverse magnetic susceptibility was always found to follow a linearly temperature dependence. The deviation from the standard superparamagnetic behavior is related to dipolar interaction among nanoparticles. The results are well explained using interacting superparamagnetic model, which is basically a mean field theory. As a consequence, the dipolar interaction affected the specific loss power of Mn0.7Zn0.3Fe2O4

GdPtPb: A noncollinear antiferromagnet with distorted kagome lattice

In the spirit of searching for Gd-based, frustrated, rare earth magnets, we have found antiferomagnetism (AF) in GdPtPb which crystallizes in the ZrNiAl-type structure that has a distorted Kagom\'e lattice of Gd-triangles. Single crystals were grown and investigated using structural, magnetic, transport and thermodynamic measurements. GdPtPb orders antiferromagnetically at 15.5 K arguably with a planar, non-collinear structure. The high temperature magnetic susceptibility data reveal an "anti-frustration" behavior having a frustration parameter, $|f|$ = $|\Theta|$/ $T_N$ = 0.25, which can be explained by mean field theory (MFT) within a two sub-lattice model. Study of the magnetic phase diagram down to $T$ = 1.8 K reveals a change of magnetic structure through a metamagnetic transition at around 20 kOe and the disappearance of the AF ordering near 140 kOe. In total, our work indicates that, GdPtPb can serve as an example of a planar, non collinear, AF with a distorted Kagom\'e magnetic sub-lattice.

3D Spin-Liquid State in an Organic Hyperkagome Lattice of Mott Dimers.

We report the first 3D spin liquid state of isotropic organic spins. Structural analysis, and magnetic and heat-capacity measurements were carried out for a chiral organic radical salt, (TBA)_{1.5}[(-)-NDI-Δ] (TBA denotes tetrabutylammonium and NDI denotes naphthalene diimide), in which (-)-NDI-Δ forms a K_{4} structure due to its triangular molecular structure and an intermolecular π-π overlap between the NDI moieties. This lattice was identical to the hyperkagome lattice of S=1/2 Mott dimers, and should exhibit 3D spin frustration. In fact, even though the high-temperature magnetic susceptibility followed the Curie-Weiss law with a negative Weiss constant of θ=-15 K, the low-temperature magnetic measurements revealed no long-range magnetic ordering down to 70mK, and suggested the presence of a spin liquid state with a large residual paramagnetism χ_{0} of 8.5×10^{-6} emu g^{-1} at the absolute zero temperature. This was supported by the ^{14}N NMR measurements down to 0.38K. Further, the low-temperature heat capacities c_{p} down to 68mK clearly indicated the presence of c_{p} for the spin liquid state, which can be fitted to the power law of T^{0.62} in the wide temperature range 0.07-4.5K.