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Spinels ( AB 2 O 4 ) with magnetic ions occupying only the octahedral B sites have inherent magnetic frustration which inhibits magnetic long-range order (LRO) but may lead to exotic states. Here we report on the magnetic properties of the tetragonal spinel Zn 0.8 Cu 0.2 FeMnO 4 , the tetragonality resulting from the Jahn-Teller active Mn 3+ ions. X-ray diffraction and x-ray photoelectron spectroscopy of the sample yielded the composition (Zn0.82+Cu0.22+) A [Fe0.42+Fe0.63+Mn3+] B O 4‒ δ . Analysis of the temperature dependence of magnetization ( M ), ac magnetic susceptibilities ( χ' and χ'' ), dc susceptibility ( χ ), heat capacity C p , and neutron diffraction (ND) measurements show complex temperature-dependent short-range order (SRO) but without LRO. The data of χ vs. T fits the Curie-Weiss law: χ = C /( T ‒ θ ) from T = 250 K to 400 K with θ ≃ 185 K signifying dominant ferromagnetic (FM) coupling with the FM exchange constant J / k B = 17 K, and C = 3.29 emu K mol ‒1 Oe ‒1 yielding an effective magnetic moment µ eff = 5.13 µ B resulting from the high-spin states of Cu 2+ ( A site) and Fe 2+ ( B site), while the B site trivalent ions Mn 3+ and Fe 3+ are in their low-spin states. The extrapolated saturation magnetization obtained from the M vs. H data at T = 2 K is explained using the spin arrangement (Cu 2+ ↓) A [Fe 2+ ↑, Fe 3+ ↓, Mn 3+ ↑] B leading to FM clusters interact antiferromagnetically at low temperatures. Temperature dependence of d( χT)/ d T shows the onset of ferrimagnetism below ∼100 K and peaks near 47 K and 24 K. The relaxation time τ obtained from temperature and frequency dependence of χ″ when fit to the power law and Vogel-Fulcher laws confirm the cluster spin-glass (SG) state. The magnetic field dependence of the SG temperatureTSGHfollows the equation:TSGH=TSG01-AH2/ϕwith T SG (0) = 46.6 K, A = 8.6 × 10 ‒3 Oe ‒0.593 andϕ= 3.37. The temperature dependence of hysteresis loops yields coercivity H C ∼ 3.8 kOe at 2 K without exchange-bias, but H C decreases with increase in T becoming zero above 24 K, the T SG ( H ) for H = 800 Oe. Variations of C p vs. T from 2 K to 200 K in H = 0 and H = 90 kOe do not show any peak characteristic of LRO. However, after correcting for the lattice contribution, a broad weak peak typically of SRO becomes evident centered around 40 K. For T < 9 K, C p varies as T 2 ; a typical signature of spin-liquids (SLs). Comparison of the ND measurements at 1.7 K and 79.4 K shows absence of LRO. Time dependence of thermo-remanent magnetization M TRM ( t ) studies below 9 K reveal weakening of the inter-cluster interaction with increase in temperature. A summary of these results is that in Zn 0.8 Cu 0.2 FeMnO 4 , ferromagnetic clusters interact antiferromagnetically without LRO but producing a cluster SG state at T SG (0) = 46.6 K, followed by SL behavior below 9 K., (© 2023 IOP Publishing Ltd.)

The nature of magnetism in the doubly-diluted spinel ZnTiCoO 4 = (Zn 2+ ) A [Ti 4+ Co 2+ ] B O 4 is reported here employing the temperature and magnetic field ( H ) dependence of dc susceptibility ( χ ), ac susceptibilities ( χ ' and χ ″), and heat capacity ( C p ) measurements. Whereas antiferromagnetic (AFM) Néel temperature T N = 13.9 K is determined from the peak in the ∂( χT )/∂ T vs T plot, the fit of the relaxation time τ (determined from the peak in the χ ″ vs T data at different frequencies) to the Power law: τ = τ 0 [( T - T SG )/ T SG ] - zν yields the spin glass freezing temperature T SG = 12.9 K, z ν ∼ 11.75, and τ 0 ∼ 10 -12 s. Since the magnitudes of τ 0 and z ν depend on the magnitude of T SG , a procedure is developed to find the optimum value of T SG = 12.9 K. A similar procedure is used to determine the optimum T 0 = 10.9 K in the Vogel-Fulcher law: τ = τ 0  exp[ E a / k B ( T - T 0 )] yielding E a / k B = 95 K, and τ 0 = 1.6 ×  10 -13 s. It is argued that the comparatively large magnitude of the Mydosh parameter Ω = 0.026 and k B T 0 / E a = 0.115 (≪1) suggests cluster spin-glass state in ZnTiCoO 4 below T SG . In the C p vs T data from 1.9 K to 50 K, only a broad peak near 20 K is observed. This and absence of λ -type anomaly near T N or T SG combined with the reduced value of change in magnetic entropy from 50 K to 1.9 K suggests only short-range AFM ordering in the system, consistent with spin-glass state. The field dependence of T SG shows slight departure ( ϕ ∼ 4.0) from the non-mean-field Almeida-Thouless line T SG ( H ) = T SG (0) (1 - AH 2/ ϕ ). Strong temperature dependence of magnetic viscosity S and coercivity H C without exchange bias, both tending to zero on approach to T SG from below, further support the spin-glass state which results from magnetic dilution driven by diamagnetic Zn 2+ and Ti 4+ ions leading to magnetic frustration. Magnetic phase diagram in the H - T plane is established using the high-field magnetization data M ( H , T ) for T < T N which reveals rapid decrease of T SG with increase in H whereas decrease in T N with increase in H is weaker, typical of AFM systems. For T > T N , the data of χ vs T are fit to the modified Curie-Weiss law, χ = χ 0 + C /( T + θ ), with χ 0 = 3.2 × 10 -4 emu mol -1 Oe -1 yielding θ = 4 K and C = 2.70 emu K mol -1 Oe -1 . This magnitude of C yields effective magnetic moment = 4.65 μ B for Co 2+ , characteristic of Co 2+ ions with some contribution from spin-orbit coupling. Molecular field theory with effective spin S = 3/2 of Co 2+ is used to determine the nearest-neighbor exchange constant J 1 / k B = 2.39 K AFM and next-nearest-neighbor exchange constant J 2 / k B = -0.66 K (ferromagnetic)., (© 2022 IOP Publishing Ltd.)

Using the analysis of the temperature and magnetic field dependence of the magnetization ( M ) measured in the temperature range of 1.5 K to 400 K in magnetic fields up to 250 kOe, the magnetic field-temperature ( H - T ) phase diagram, tricritical point and exchange constants of the antiferromagnetic MnTa 2 O 6 are determined in this work. X-ray diffraction/Rietveld refinement and x-ray photoelectron spectroscopy of the polycrystalline MnTa 2 O 6 sample verified its phase purity. Temperature dependence of the magnetic susceptibility χ (= M / H ) yields the Néel temperature T N = 5.97 K determined from the peak in the computed ∂( χT )/∂ T vs T plot, in agreement with the T N = 6.00 K determined from the peak in the C P vs T data. The experimental data of C P vs T near T N is fitted to C P = A | T - T N | - α yielding the critical exponent α = 0.10(0.13) for T > T N ( T < T N ). The χ vs T data for T > 25 K fits well with the modified Curie-Weiss law: χ = χ 0 + C /( T - θ ) with χ 0 = -2.12 × 10 -4 emu mol -1  Oe -1 yielding θ = -24 K, and C = 4.44 emu K mol -1  Oe -1 , the later giving magnetic moment μ = 5.96  μ B per Mn 2+ ion. This yields the effective spin S = 5/2 and g = 2.015 for Mn 2+ , in agreement with g = 2.0155 measured using electron spin resonance spectroscopy. Using the magnitudes of θ and T N and molecular field theory, the antiferromagnetic exchange constants J 0 / k B = -1.5 ± 0.2 K and J ⊥ / k B = -0.85 ± 0.05 K for Mn 2+ ions along the chain c -axis and perpendicular to the c -axis respectively are determined. The χ vs T data when compared to the prediction of a Heisenberg linear chain model provides semiquantitative agreement with the observed variation. The H - T phase diagram is mapped using the M - H isotherms and M - T data at different H yielding the tricritical point T TP ( H , T ) = (17.0 kOe, 5.69 K) separating the paramagnetic, antiferromagnetic, and spin-flop phases. At 1.5 K, the experimental magnitudes of the exchange field H E = 206.4 kOe and spin-flop field H SF = 23.5 kOe yield the anisotropy field H A = 1.34 kOe. These results for MnTa 2 O 6 are compared with those reported recently in the isostructural MnNb 2 O 6 ., (© 2022 IOP Publishing Ltd.)

This work presents the magnetic field-temperature ( H - T ) phase diagram, exchange constants, specific heat ( C P ) exponents and magnetic ground state of the antiferromagnetic MnNb 2 O 6 polycrystals. Temperature dependence of the magnetic susceptibility χ (= M / H ) yields the Néel temperature T N = 4.33 K determined from the peak in the computed ∂( χT )/∂ T vs T plot in agreement with the transition in the C P vs T data at T N = 4.36 K. The experimental data of C P vs T near T N is fitted to C P = A | T - T N | - α yielding the critical exponent α = 0.12 (0.15) for T > T N ( T < T N ). The best fit of χ vs T data for T > 50 K to χ = χ 0 + C /( T - θ ) with χ 0 = -1.85 × 10 -4 emu mol -1 Oe -1 yields θ = -17 K, and C = 4.385 emu K mol -1 Oe -1 , the latter giving magnetic moment μ = 5.920 μ B per Mn 2+ ion. This confirms the effective spin S = 5/2 and g = 2.001 for Mn 2+ and the dominant exchange interaction being antiferromagnetic in nature. Using the magnitudes of θ and T N and molecular field theory (MFT), the exchange constants J 0 / k B = -1.08 K for Mn 2+ ions along the chain c -axis and J ⊥ / k B = -0.61 K as the interchain coupling perpendicular to c -axis are determined. These exchange constants are consistent with the expected χ vs T variation for the Heisenberg linear chain. The H - T phase diagram, mapped using the M - H isotherms and M - T data at different H combined with the reported data of Nielsen et al , yields a triple-point T TP ( H , T ) = (18 kOe, 4.06 K). The spin-flopped state above T TP and the forced ferromagnetism for H > 192 kOe are used to estimate the anisotropy energy H A ≈ 0.8 kOe., (© 2021 IOP Publishing Ltd.)

The structure, magnetic, and magnetocaloric (MC) properties of orthorhombic nanocrystalline GdCrO 3 with six particle sizes: ⟨ d ⟩ = 87, 103, 145, 224, 318, and 352 nm are reported. The particle size was tailored by annealing under different temperatures and estimated by scanning electron microscopy. With increase in ⟨ d ⟩, Goldschmidt tolerance factor t , orthorhombic strain s , and out-of-plane Cr-O 1 -Cr bond angle first decrease, reaching minimum values for ⟨ d ⟩ = 224 nm, and then increase for sample with ⟨ d ⟩ = 318 nm and 352 nm, thus showing a V-shaped variation. Temperature dependence of the magnetization ( M ) reveals an antiferromagnetic transition atTNCr∼168K for ⟨ d ⟩ ⩾ 224 nm andTNCr∼167K for ⟨ d ⟩ < 224 nm and an essentially d -independent spin-reorientation at T SR = 9 K. M measured at 5 K and 7 T first increases with increase in ⟨ d ⟩, reaching maximum value for sample with ⟨ d ⟩ = 224 nm, and then decreases for samples with ⟨ d ⟩ = 318 nm and 352 nm, showing an inverted-V variation with ⟨ d ⟩. Similar ⟨ d ⟩-dependence is observed for the magnetic entropy change (MEC) and relative cooling power (RCP) showing a close relationship between the structural and magnetic properties of GdCrO 3 nanoparticles investigated here. The 224 nm sample with the minimum values of t , s , and Cr-O 1 -Cr bond angle exhibits the maximum value of MEC (-Δ S ) = 37.8 J kg -1  K -1 at 5 K under a field variation (Δ H ) of 7 T and its large estimated RCP of 623.6 J Kg -1 is comparable with those of typical MC materials. Both (-Δ S ) and RCP are shown to scale with the saturation magnetization M S , suggesting that M S is the crucial factor controlling their magnitudes. Assuming (-Δ S ) ∼ (Δ H ) n , the temperature dependence of n for the six samples are determined, n varying between 1.3 at 5 K to n = 2.2 at 130 K in line with its expected magnitudes based on mean-field theory. These results on structure-property correlations and scaling in GdCrO 3 suggest that its MC properties are tunable for potential low-temperature magnetic refrigeration applications., (© 2021 IOP Publishing Ltd.)

Static and dynamic magnetic properties of normal spinel Co 2 RuO 4 = (Co 2+ )A[Co3+Ru3+]BO4are reported based on our investigations of the temperature ( T ), magnetic field ( H ) and frequency ( f ) dependence of the ac-magnetic susceptibilities and dc-magnetization ( M ) covering the temperature range T = 2 K-400 K and H up to 90 kOe. These investigations show that Co 2 RuO 4 exhibits an antiferromagnetic (AFM) transition at T N ∼ 15.2 K, along with a spin-glass state at slightly lower temperature ( T SG ) near 14.2 K. It is argued that T N is mainly governed by the ordering of the spins of Co 2+ ions occupying the A -site, whereas the exchange interaction between the Co 2+ ions on the A -site and randomly distributed Ru 3+ on the B -site triggers the spin-glass phase, Co 3+ ions on the B -site being in the low-spin non-magnetic state. Analysis of measurements of M ( H , T ) for T < T N are used to construct the H - T phase diagram showing that T SG shifts to lower T varying as H 2/3.2 expected for spin-glass state whereas T N is nearly H -independent. For T > T N , analysis of the paramagnetic susceptibility ( χ ) vs. T data are fit to the modified Curie-Weiss law, χ = χ 0 + C /( T + θ ), with χ 0 = 0.0015 emu mol -1 Oe -1 yielding θ = 53 K and C = 2.16 emu-K mol -1 Oe -1 , the later yielding an effective magnetic moment μ eff = 4.16 μ B comparable to the expected value of μ eff = 4.24 μ B per Co 2 RuO 4 . Using T N , θ and high temperature series for χ , dominant exchange constant J 1 / k B ∼ 6 K between the Co 2+ on the A -sites is estimated. Analysis of the ac magnetic susceptibilities near T SG yields the dynamical critical exponent zν = 5.2 and microscopic spin relaxation time τ 0 ∼ 1.16 × 10 -10 sec characteristic of cluster spin-glasses and the observed time-dependence of M ( t ) is supportive of the spin-glass state. Large M - H loop asymmetry at low temperatures with giant exchange bias effect ( H EB ∼ 1.8 kOe) and coercivity ( H C ∼ 7 kOe) for a field cooled sample further support the mixed magnetic phase nature of this interesting spinel. The negative magnetocaloric effect observed below T N is interpreted to be due to the AFM and SG ordering. It is argued that the observed change from positive MCE (magnetocaloric effect) for T > T N to inverse MCE for T < T N observed in Co 2 RuO 4 (and reported previously in other systems also) is related to the change in sign of (∂ M /∂ T ) vs. T data., (© 2020 IOP Publishing Ltd.)

La 0.7 Sr 0.3 MnO 3 , a strong semi-metallic ferromagnet having robust spin polarization and magnetic transition temperature (T C ) well above 300 K, has attracted significant attention as a possible candidate for a wide range of memory, spintronic, and multifunctional devices. Since varying the oxygen partial pressure during growth is likely to change the structural and other physical functionalities of La 0.7 Sr 0.3 MnO 3 (LSMO) films, here we report detailed investigations on structure, along with magnetic behavior of LSMO films with same thickness (~30 nm) but synthesized at various oxygen partial pressures: 10, 30, 50, 100, 150, 200 and 250 mTorr. The observation of only (00 l) reflections without any secondary peaks in the XRD patterns confirms the high-quality synthesis of the above-mentioned films. Surface morphology of the films reveals that these films are very smooth with low roughness, the thin films synthesized at 150 mTorr having the lowest average roughness. The increasing of magnetic T C and sharpness of the magnetic phase transitions with increasing oxygen growth pressure suggests that by decreasing the oxygen growth pressure leads to oxygen deficiencies in grown films which induce oxygen inhomogeneity. Thin films grown at 150 mTorr exhibits the highest magnetization with T C  = 340 K as these thin films possess the lowest roughness and might exhibit lowest oxygen vacancies and defects. Interpretation and significance of these results in the 30 nm LSMO thin films prepared at different oxygen growth pressures are also presented, along with the existence and growth pressure dependence of negative remanent magnetization (NRM) of the above-mentioned thin films.

The observation of inverted magnetic hysteresis loops and negative magnetic remanence (NRM) in a 7.6 nm thin film of La 0.7 Sr 0.3 MnO 3 grown on SrTiO 3 substrates is reported. The film was grown employing pulsed laser deposition and characterized by reflection high-energy electron diffraction during growth and using x-ray reflectivity measurements post-growth. Magnetic properties of the film were measured from 5 K to 400 K under both the field-cooled (FC) and zero-field-cooled (ZFC) conditions. The observed results of inverted magnetic hysteresis loops and NRM are interpreted in terms of the co-existence of a magnetically inhomogeneous region consisting of superparamagnetic spin clusters with a blocking temperature T B   =  240 K and the ferromagnetic state with an ordering temperature T C   =  290 K. Hysteresis loop inversion is observed in the temperature region of T B   <  T  <  T C whereas NRM appears in the mixed superparamagnetic and ferromagnetic states for T  <  T C down to 5 K. These observations of hysteresis loop inversion and NRM are related to the magneto-static interaction between the superparamagnetic and ferromagnetic phases leading to anti-alignment of spin of both magnetic phases with respect to each other.

Reported here are the results and their analysis from our detailed investigations of the effects of Cu doping ([Formula: see text]) on the electronic structure and magnetic properties of the spinel [Formula: see text]O 4 . A detailed comparison is given for the [Formula: see text] and [Formula: see text] cases for both the bulk-like samples and nanoparticles. The electronic structure determined from x-ray photoelectron spectroscopy and Rietveld analysis of x-ray diffraction patterns shows the structure to be: ([Formula: see text]) A [Formula: see text] [Formula: see text] [Formula: see text]] B [Formula: see text] i.e. [Formula: see text] substitutes for [Formula: see text] on the octahedral B-sites. For the bulk samples, the ferrimagnetic [Formula: see text] K for [Formula: see text] is lowered to [Formula: see text] K for the [Formula: see text] sample, this decrease being due to the effect of Cu doping. For the nanosize [Formula: see text] ([Formula: see text]) sample, the lower [Formula: see text] K ([Formula: see text] K) is observed using [Formula: see text] analysis, this lowering being due to finite size effects. For [Formula: see text], fits of dc paramagnetic susceptibility data of [Formula: see text] versus T in nanosize samples to the Néel expression are used to determine the exchange interactions between the A and B sites with exchange constants: [Formula: see text] K (4.1 K), [Formula: see text] K (16.3 K) and [Formula: see text] K (13.8 K) for [Formula: see text]. The temperature dependence of ac susceptibilities [Formula: see text] and [Formula: see text] at different frequencies shows that in bulk samples of [Formula: see text] and [Formula: see text], the transition at T C is the normal second order transition. But for the nanosize [Formula: see text] and 0.2 samples, analysis of the ac susceptibilities shows that the ferrimagnetic transition at T C is followed by a re-entrant spin-glass transition at lower temperatures [Formula: see text] K (138 K) for [Formula: see text] ([Formula: see text]). Analysis of the ac susceptibilities, [Formula: see text] and [Formula: see text], versus T data is done in terms of two scaling laws: (i) Vogel-Fulcher law [Formula: see text] [Formula: see text]; and (ii) power law of critical slowing-down [Formula: see text]. These fits confirm the existence of glassy behavior below T SG with the parameters [Formula: see text] (8.91), [Formula: see text] (9.6  ×  10[Formula: see text]) and [Formula: see text] K (∼138 K) for the samples [Formula: see text] (0.2), with similar results obtained for other samples. The linear behavior of the peak maximum in [Formula: see text] versus [Formula: see text] (AT-line) further supports the existence of glassy states in nanosize samples. For [Formula: see text], the temperature and composition dependence of the hysteresis loop parameters are investigated; all the samples with x  ⩾  0.1 have the coercivity H C and remanence [Formula: see text]. Since the results reported here in these nanostructures are significantly different from those in bulk [Formula: see text] [Formula: see text], further investigations of their magnetic structures using neutron diffraction are warranted.

Detailed investigations of the magnetic properties of the layered system β-Co(OH) 2 are presented. X-ray diffraction and scanning electron microscopy of the sample show it to consist of hexagonal nanosheets with thickness  ≈30 nm and width ~100 nm-200 nm. Analysis of its measured magnetization (M) as a function of temperature (T  =  2 K to 300 K) and magnetic field (H up to 90 kOe) yields a Neel temperature T N   =  9.2 K. This lower T N   =  9.2 K, compared to T N   =  11.6 K reported for bulk β-Co(OH) 2 , is due to finite-size effects. Analysis of the data for T  >  T N shows that the M versus T data does not quite fit the Curie-Weiss law since both the Curie constant C and Weiss temperature θ have noticeable temperature dependence. This temperature dependence is interpreted to be due to the effect of spin-orbit coupling, yielding a low-temperature effective spin S  =  1/2 ground state with magnetic moment µ  =  4.745 µ B and g  =  5.479. For T  <  T N , M versus H data show two transitions, first at H C1   ≃  15 kOe and second at H C2   ≃  32 kOe. The transition at H C1 is a spin-flop transition and H C2 is due to forced alignment of the spins yielding saturation magnetization M S   =  160 emu g -1 at 2 K, in agreement with the calculated M S   =  163 emu g -1 for the complete alignment of the spins at T  =  0 K for the spin S  =  1/2 ground state with g  =  5.479. The fitting of the M versus T data for T  >  T N to the high temperature series for S  =  1/2 XY model yields the in-plane ferromagnetic exchange constant J 1 /k B   =  (1.8  ±  0.2) K for Co 2+ ions, with the interplane exchange constant J 2 /k B   ≃  -0.2 K determined from the magnitude of T N . The temperature dependence of H C1 and H C2 is presented and discussed.

Structural properties of sixteen (16) commercial samples of graphene-based materials (GBM) labelled as graphene, graphene oxide or reduced graphene oxide are investigated at room temperature using X-ray diffraction (XRD) and Raman spectroscopy. Based on the observed correlation between the results obtained with these two techniques, these samples are classified into three groups: Group A of seven samples consisting of graphitic nanosheets with evaluated thickness ≃20 nm and exhibiting both the 2H and 3R phases in XRD; Group B of six samples exhibiting XRD spectra characteristic of either graphene oxides (GO) or carbons with some order; and Group C of three samples with XRD spectra characteristic of disordered carbons. The relative intensities and widths of D, G, D', 2D and (D + D') bands in the Raman spectra are equally distinguishable between the samples in groups A, B and C. The width of the D-band is the smallest for Group A samples, intermediate for group B and the largest for group C samples. The intensity ratio I(D)/I(G) of the D and G bands in the Raman spectra of the samples is used to quantify the Raman-active defects whose concentration increases in going from samples in Group A to those in Group C.

Background: Graphene, a monolayer of carbon, is an engineered nanomaterial (ENM) with physical and chemical properties that may offer application advantages over other carbonaceous ENMs, such as carbon nanotubes (CNT). The goal of this study was to comparatively assess pulmonary and systemic toxicity of graphite nanoplates, a member of the graphene-based nanomaterial family, with respect to nanoplate size., Methods: Three sizes of graphite nanoplates [20 μm lateral (Gr20), 5 μm lateral (Gr5), and <2 μm lateral (Gr1)] ranging from 8-25 nm in thickness were characterized for difference in surface area, structure,, zeta potential, and agglomeration in dispersion medium, the vehicle for in vivo studies. Mice were exposed by pharyngeal aspiration to these 3 sizes of graphite nanoplates at doses of 4 or 40 μg/mouse, or to carbon black (CB) as a carbonaceous control material. At 4 h, 1 day, 7 days, 1 month, and 2 months post-exposure, bronchoalveolar lavage was performed to collect fluid and cells for analysis of lung injury and inflammation. Particle clearance, histopathology and gene expression in lung tissue were evaluated. In addition, protein levels and gene expression were measured in blood, heart, aorta and liver to assess systemic responses., Results: All Gr samples were found to be similarly composed of two graphite structures and agglomerated to varying degrees in DM in proportion to the lateral dimension. Surface area for Gr1 was approximately 7-fold greater than Gr5 and Gr20, but was less reactive reactive per m(2). At the low dose, none of the Gr materials induced toxicity. At the high dose, Gr20 and Gr5 exposure increased indices of lung inflammation and injury in lavage fluid and tissue gene expression to a greater degree and duration than Gr1 and CB. Gr5 and Gr20 showed no or minimal lung epithelial hypertrophy and hyperplasia, and no development of fibrosis by 2 months post-exposure. In addition, the aorta and liver inflammatory and acute phase genes were transiently elevated in Gr5 and Gr20, relative to Gr1., Conclusions: Pulmonary and systemic toxicity of graphite nanoplates may be dependent on lateral size and/or surface reactivity, with the graphite nanoplates > 5 μm laterally inducing greater toxicity which peaked at the early time points post-exposure relative to the 1-2 μm graphite nanoplate.

Previous magnetic studies in the organic semiconductor β-manganese phthalocyanine (β-MnPc) have reported it to be a canted ferromagnet below T(C)  ≈  8.6 K. However, the recent result of the lack of a λ-type anomaly in the specific heat versus temperature data near the quoted T(C) has questioned the presence of long-range 3-dimensional (3D) magnetic ordering in this system. In this paper, detailed measurements and analysis of the temperature (2 K-300 K) and magnetic field (up to 90 kOe) dependence of the dc and ac magnetic susceptibilities in a powder sample of β-MnPc leads us to conclude that 3D long-range magnetic ordering is absent in this material. This is supported by the Arrott plots and the lack of a peak in the ac susceptibilities, χ' and χ″, near the quoted T(C). Instead, the system can be best described as an Ising-like chain magnet with Arrhenius relaxation of the magnetization governed by an intra-layer ferromagnetic exchange constant J/k(B)  =  2.6 K and the single ion anisotropy energy parameter |D|/k(B)  =  8.3 K. The absence of 3D long range order is consistent with the measured |D|/  >  J.

Graphene-based material (GBM) samples acquired from commercial sources are investigated using X-ray diffraction (XRD). Of the 18 GBM samples investigated here, seven samples show XRD patterns with features characteristic of the graphite structure. The XRD patterns of the seven samples are analyzed showing the presence of both the ABA (2H) structure and the ABCA (3R) structure. After de-convoluting the (101) lines of the 2H and 3R structures, the areas under the peaks are used to determine the relative concentrations of the 2H and 3R phases present, typically yielding the ratio 60/40 for 2H/3R. The presence of the 3R structure is important since the 3R structure is a semiconductor with tunable band gap and it is less stable than the 2H structure. The number of layers determined from the analysis of the XRD data varies between 65 and 109 for different samples yielding thickness of the graphite sheets varying between 22 nm and 37 nm. Scanning electron microscopy and transmission electron microscopy of three representative samples confirms the sheet-like morphology and stacking of the graphene layers in the samples. Relevance of these results in connection with their potential applications and toxicology is briefly discussed.

In the spinel Co2SnO4, coexistence of ferrimagnetic ordering below T(N) ≃ 41 K followed by a spin glass state below T(SG) ≃ 39 K was proposed recently based on the temperature dependence of magnetization M(T) data. Here new measurements of the temperature dependence of the specific heat C(P)(T), ac-susceptibilities χ'(T) and χ″(T) measured at frequencies between 0.51 and 1.2 kHz, and the hysteresis loop parameters (coercivity H(C)(T) and remanence M(R)(T)) in two differently prepared samples of Co2SnO4 are reported. The presence of the Co(2+) and Sn(4+) states is confirmed by x-ray photoelectron spectroscopy (XPS) yielding the structure: Co2SnO4 = [Co(2+)][Co(2+)Sn(4+)]O4. The data of C(P) versus T shows only an inflection near 39 K characteristic of spin-glass ordering. The analysis of the frequency dependence of ac-magnetic susceptibility data near 39 K using the Vogel-Fulcher law and the power-law of the critical slowing-down suggests the presence of spin clusters in the system which is close to a spin-glass state. With a decrease in temperature below 39 K, the temperature dependence of the coercivity H(C) and remanence M(R) for the zero-field cooled samples show both H(C) and M(R) reaching their peak magnitudes near 25 K, then decreasing with decreasing T and becoming negligible below 15 K. The plot of C(P)/T versus T also yields a weak inflection near 15 K. This temperature dependence of H(C) and remanence M(R) is likely associated with the different magnitudes of the magnetic moments of Co(2+) ions on the 'A' and 'B' sites and their different temperature dependence.

Abstract The potential applications of cellulose nanomaterials in advanced composites and biomedicine makes it imperative to understand their pulmonary exposure to human health. Here, we report the results on the biodurability of three cellulose nanocrystal (CNC), two cellulose nanofibril (CNF) and a benchmark cellulose microcrystal (CMC) when exposed to artificial lung airway lining fluid (SUF, pH 7.3) for up to 7 days and alveolar macrophage phagolysosomal fluid (PSF, pH 4.5) for up to 9 months. X-ray diffraction analysis was used to monitor biodurability and thermogravimetry, surface area, hydrodynamic diameter, zeta potential and free radical generation capacity of the samples were determined (in vitro cell-free and RAW 264.7 cell line models). The CMC showed no measurable changes in crystallinity (x(CR)) or crystallite size D in either SUF or PSF. For one CNC, a slight decrease in x(CR) and D in SUF was observed. In acidic PSF, a slight increase in x(CR) with exposure time was observed, possibly due to dissolution of the amorphous component. In a cell-free reaction with H₂O₂, radicals were observed; the CNCs and a CNF generated significantly more ·OH radicals than the CMC (p < 0.05). The ·OH radical production correlates with particle decomposition temperature and is explained by the higher surface area to volume ratio of the CNCs. Based on their biodurability, mechanical clearance would be the primary mechanism for lung clearance of cellulose materials. The production of ·OH radicals indicates the need for additional studies to characterize the potential inhalation hazards of cellulose.

The nature of magnetic ordering in quasi-2D layered hydroxide of Ni (LH-Ni-DS) with hexagonal structure and synthesized by intercalating dodecyl sulfate (DS) ligand, (C12H25OSO3)(-), between the layers using a hydrothermal technique is investigated. The observation of (00l) peaks up to l = 8 in x-ray diffraction on the sample yields an interlayer spacing c ≃ 30.5 Å and a crystallite size ≃ 16 nm. Assignment of the lines observed in the FTIR spectra to the various groups of the DS ligand confirms the intercalation. From the analysis of detailed investigations of the temperature dependence of the magnetization M at different magnetic fields, ac susceptibilities at frequencies from 0.1 to 1 kHz, and electron magnetic resonance spectra at 9.28 GHz, it is concluded that LH-Ni-DS orders ferromagnetically at TC ≃ 23 K. This TC is about 45% higher than TC ≃ 16 K reported for LH-Ni-Ac with c ≃ 8.6 Å obtained by intercalating an acetate ligand between the layers. The roles of the interlayer dipolar interaction, magnetic anisotropy and exchange interactions in determining TC in LH-Ni-L systems for several ligands L yielding different c-axes are discussed.

Gene therapy is a promising therapeutic approach for treating disease, but the efficient delivery of genes to desired locations with minimal side effects remains a challenge. In addition to gene therapy, it is also highly desirable to provide sensitive imaging information in patients for disease diagnosis, screening and post-therapy monitoring. Here, we report on the development of dual-purpose chitosan and polyethyleneimine (PEI) coated magnetic micelles (CP-mag-micelles) that can deliver nucleic acid-based therapeutic agents and also provide magnetic resonance imaging (MRI). These 'theranostic' CP-mag-micelles are composed of monodisperse hydrophobic superparamagnetic iron oxide nanoparticles (SPIONs) loaded into the cores of micelles that are self-assembled from a block copolymer of poly (D, L-lactide) (PLA) and monomethoxy polyethylene glycol (mPEG). For efficient loading and protection of the nucleic acids the micelles were coated with cationic polymers, such as chitosan and PEI. The morphology and size distribution of the CP-mag-micelles were characterized and their potential for use as an MRI-probe was tested using an MRI scanner. The T(2) relaxivity of mag-micelles was similar to CP-mag-micelles confirming that coating with cationic polymers did not alter magnetism. Nanoparticles coated with chitosan:PEI at a weight ratio of 5:5 showed higher transfection efficiency in HEK293, 3T3 and PC3 cells than with weight ratios of 3:7 or 7:3. CP-mag-micelles are biocompatible, can be delivered to various organs and are safe. A single injection of CP-mag-micelles carrying reporter plasmids in vivo expressed genes for at least one week. Collectively, our results demonstrate that a structural reinforcement of SPIONs loaded in the core of an mPEG-PLA micelle coated with cationic polymers provides efficient DNA delivery and enhanced MRI potential, and affords a promising candidate for theranostics in the future., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Palladium (Pd) nanoparticle catalysts were successfully synthesized within an aqueous phase using sodium carboxymethyl cellulose (CMC) as a capping ligand which offers a green alternative to conventional nanoparticle synthesis techniques. The CMC-stabilized Pd nanoparticles were subsequently dispersed within support materials using the incipient wetness impregnation technique for utilization in heterogeneous catalyst systems. The unsupported and supported (both calcined and uncalcined) Pd nanoparticle catalysts were characterized using transmission electron microscopy, energy dispersive x-ray spectrometry, x-ray diffraction, and Brunauer-Emmett-Teller surface area measurement and their catalytic activity toward the hydrodechlorination of trichloroethylene (TCE) in aqueous media was examined using homogeneous and heterogeneous catalyst systems, respectively. The unsupported Pd nanoparticles showed considerable activity toward the degradation of TCE, as demonstrated by the reaction kinetics. Although the supported Pd nanoparticle catalysts had a lower catalytic activity than the unsupported particles that were homogeneously dispersed in the aqueous solutions, the supported catalysts retained sufficient activity toward the degradation of TCE. In addition, the use of the hydrophilic Al(2)O(3) support material induced a mass transfer resistance to TCE that affected the initial hydrodechlorination rate. This paper demonstrates that supported Pd catalysts can be applied to the heterogeneous catalytic hydrodechlorination of TCE.

The magnetic anisotropy of ferromagnetic (FM) Ni, Co, and Fe polycrystalline thin films grown on antiferromagnetic (AF) FeF(2)(110) epitaxial layers was studied, as a function of temperature, using ferromagnetic resonance. In addition to an in-plane anisotropy in the FM induced by fluctuations in the AF short-range order, a perpendicular (biquadratic) magnetic anisotropy, with an out-of-plane component, was found which increased with decreasing temperature above the AF Neél temperature (T(N) = 78.4 K). This is a surprising result given that the AF's uniaxial anisotropy axis was in the plane of the sample, but is consistent with prior experimental and theoretical work. The resonance linewidth had a strong dependence on the direction of the external magnetic field with respect to in-plane FeF(2) crystallographic directions, consistent with interface magnon scattering due to defect-induced demagnetizing fields. Below T(N), the exchange bias field H(E) measured via FMR for the Ni sample was in good agreement with H(E) determined from magnetization measurements if the perpendicular out-of-plane anisotropy was taken into account. A low field resonance line normally observed at H ≈ 0, associated with domain formation during magnetization in ferromagnets, coincided with the exchange bias field for T < T(N), indicating domain formation with the in-plane FM magnetization perpendicular to the AF easy axis. Thus, biquadratic FM-AF coupling is important at temperatures below and above T(N)., (© 2012 IOP Publishing Ltd)

The two layered hexagonal hydroxides of Ni are β-Ni(OH)(2) and α-Ni(OH)(2); β-Ni(OH)(2) is now known to be an antiferromagnet whereas the nature of the magnetism in α-Ni(OH)(2) is not yet well established. Here, the magnetic properties of α-Ni(OH)(2) with lattice parameters a = 3.02 Å and c = 8.6 Å, and flower-like morphology with petal thickness of approximately equal to 50 Å are reported. Temperature (2-300 K) and magnetic field (up to 65 kOe) dependence of the magnetization and ac susceptibility at f = 0.1-1000 Hz were measured. Analysis of the data yields ferromagnetic ordering in the system with T(C) is approximately equal to 16 K. In addition, a nanosize related blocking temperature T(B) = 8 K and spin-glass-like ordering of the surface spins near 3.5 K are inferred from the ac frequency and dc magnetic field dependence of these transitions. Fitting to the high temperature series and quasi-2D nature of the system is used to determine J(1)/k(B) = 4.38 K (J(2)/k(B) = 0.14 K) for the intraplane (interplane) exchange coupling between the Ni(2+) ions.

Investigations of spin dynamics in Ni nanoparticles (NPs) with diameters D = 3.8, 11.7, 15 and 21 nm embedded in an amorphous SiO(2) matrix of composition 15/85 (Ni/SiO(2)) are reported using EMR (electron magnetic resonance) spectroscopy at 9.28 GHz. Three resonance lines are observed whose EMR parameters, namely linewidth ΔH, resonance field H(r) and intensity I(o), are measured from 5 to 300 K. Line 1 with temperature-independent ΔH = 50 Oe and g≈2, and intensity varying as 1/T, is shown to result from paramagnetic defects in the SiO(2) matrix. Lines 2 and 3, with g≈2.2 and 8, respectively, and temperature-dependent EMR parameters are assigned to Ni NPs. While line 2 with g≈2.2 is due to the majority of Ni NPs, the source of line 3 is discussed in terms of two possibilities: (i) large clusters of blocked Ni NPs and (ii) the inherent part of the composite asymmetric line made up of lines 2 and 3 predicted by the Raikher-Stepanov (RS) model for dispersed ferromagnets. The temperature dependence of ΔH (full width at half-maximum) of the composite line obtained by integration of the EMR spectra decreases with the increase in temperature, reaching a minimum near 300 K in agreement with the RS model. The observed decreasing asymmetry of the composite absorption spectra with increasing temperature is also in agreement with the predictions of the RS model, thus providing a satisfactory explanation for the observed temperature dependence of the EMR spectra of Ni NPs. Large clusters of blocked Ni NPs as the source of line 3 are ruled out and additional tests for the RS model are proposed. The decreasing magnetization with decreasing particle size of Ni NPs observed here is discussed in terms of the possible roles of the surface disordered spins and Ni-SiO(2) interaction.

Combustion experiments were carried out on four different residual fuel oils in a 732-kW boiler. PM emission samples were separated aerodynamically by a cyclone into fractions that were nominally less than and greater than 2.5 microns in diameter. However, examination of several of the samples by computer-controlled scanning electron microscopy (CCSEM) revealed that part of the PM2.5 fraction consists of carbonaceous cenospheres and vesicular particles that range up to 10 microns in diameter. X-ray absorption fine structure (XAFS) spectroscopy data were obtained at the S, V, Ni, Fe, Cu, Zn, and As K-edges and at the Pb L-edge. Deconvolution of the X-ray absorption near edge structure (XANES) region of the S spectra established that the dominant molecular forms of S present were sulfate (26-84% of total S) and thiophene (13-39% of total S). Sulfate was greater in the PM2.5 samples than in the PM2.5+ samples. Inorganic sulfides and elemental sulfur were present in lower percentages. The Ni XANES spectra from all of the samples agreed fairly well with that of NiSO4, while most of the V spectra closely resembled that of vanadyl sulfate (VO.SO4.xH2O). The other metals investigated (i.e., Fe, Cu, Zn, and Pb) also were present predominantly as sulfates. Arsenic was present as an arsenate (As+5). X-ray diffraction patterns of the PM2.5 fraction exhibit sharp lines due to sulfate compounds (Zn, V, Ni, Ca, etc.) superimposed on broad peaks due to amorphous carbons. All of the samples contain a significant organic component, with the loss on ignition (LOI) ranging from 64 to 87% for the PM2.5 fraction and from 88 to 97% for the PM2.5+ fraction. Based on 13C nuclear magnetic resonance (NMR) analysis, the carbon is predominantly condensed in graphitic structures. Aliphatic structure was detected in only one of seven samples examined.

Surface IR (infrared) modes of crystalline and fumed (amorphous) silica particles, calcined at temperatures up to 1095 degrees C, have been studied by Fourier transform infrared spectroscopy. The ability of these same particles to lyse cells has been measured by a hemolysis protocol. The untreated crystalline and amorphous materials differ by a factor of 40 in specific surface area, and the intensity per unit mass of the sharp surface silanol band near 3745 cm-1 in the amorphous material is an order of magnitude larger than in the crystalline material. A similar difference is observed in the lysing potential of the two materials. The intensity of the silanol band increases after calcination for both materials, reaching peak values near 500 degrees C, followed by a dramatic drop at higher calcination temperatures, and reaching negligible values for materials calcined near 1100 degrees C. The lysing potential data follow essentially the same pattern for both crystalline and fumed silica. These results are consistent with the hypothesis that the surface silanol groups are involved in cell lysis. Further experiments are suggested to evaluate the relationship between the surface structure of silica particles and their potential cytotoxicity.

The chemiluminescence (CL) response of guinea pig peritoneal macrophages to immune precipitates and soluble immune complexes has been investigated. The rapid burst of intense light emission observed in response to both stimuli, was inhibited by superoxide dismutase (SOD). With soluble immune complexes, this was followed by prolonged CL of lower intensity susceptible to both SOD and catalase inhibition. The magnitude of the CL response was directly related to seize the size of the soluble complexes reacting with the macrophages. These findings suggest that circulating, as distinct from deposited immune complexes, may play a role in the pathogenesis of complex-mediated diseases.