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We have investigated Co-doped TiO[sub 2] thin films grown by reactive co-sputtering. X-ray diffraction showed a single phase polycrystalline rutile structure, without any segregation of Co into particulates within the instrumental resolution limit. The atomic content of Co ranged from 1% to 12%. The temperature dependence of resistivity showed an extrinsic semiconducting behavior. From optical absorption measurements, the band gap E[sub g] ≈ 3.2 5 ± 0.0 5 eV was found, independent of the Co concentration, and in agreement with a literature value. Room temperature M-H loops showed a ferromagnetic behavior for Co content higher than 3%. The magnetic moment per Co atom was estimated to be about 0.94 µ[sub B], suggesting a low spin configuration of Co ions. The temperature dependence of remanent magnetization revealed a Curie temperature higher than 400 K for Co content of 12%. [ABSTRACT FROM AUTHOR]

Discusses a study on amorphous thin films of bismuth-iron-oxygen-lead-zirconium-oxygen. Techniques used to prepare the films; Effects of sputtering conditions and annealing at high temperature on magnetic properties of such films; Analysis of the room-temperature magnetization.

Deals with a study on the magnetic properties of an intermetallic when mischmetal is used as the rare-earth component for both a hydrided and unhydrided compound in the case of mischmetal nickel-iron intermetallic. Mössbauer effect measurements; Findings of scanning electron microscopy; Assessment of the hybriding process of iron.

Details a study which analyzed the structural and magnetic characteristics of radio frequency sputtered thin films of La[sub0.74]Pb[sub0.26]MnO[subz] on silicon. Methodology of the study; Measurement of magnetization properties; Temperature dependence of magnetization.

Observation of significant negative exchange bias (HE) is reported in solid solutions of single-phase samples of Dy1-x Ndx Cr O3 for x = 0.33,0.67, and 1 with corresponding Néel temperatures at TNCr = 175K,200K, and 225 K, respectively, and the spin-reorientation transitions TSR at 48 K, 58 K, and 38 K, respectively. In contrast, no HE was observed for the sample with x = 0 (i.e., DyCrO3) shows no HE below its TNCr = 145K, and no reorientation of spins at lower temperatures was observed. More importantly, the (negative) HE for the x = 0.33,0.67, and 1 samples is observed only in the temperature range between TN and TSR with the corresponding observation of magnetic coercivity. These results show that the canted antiferromagnetic Γ7,Cr structure of the Cr3+ moments present between TNCr and TSR is essential for the observed HE. By comparing this result to the literature, common features of single-phase materials with HE were identified. The present bulk powder samples were prepared by the citrate method and structurally characterized by x-ray diffraction and Raman spectroscopy techniques. Neutron diffraction measurements for the x = 0.33,0.67, and 1 samples at select temperatures were done to verify the presence of the Γ7,Cr structure between TNCr and TSR and the Γ1,Cr structure (with no canting of Cr3+ moments) below TSR. [ABSTRACT FROM AUTHOR]

Anisotropic diamagnetism of pristine graphite and graphene is well known. Here, evidence of significant induced ferromagnetism in multilayer graphene (MLG) decorated with ferrimagnetic Fe3O4 particles is reported. This MLG-Fe3O4 nano-composite was prepared by a one-step ultrasonic treatment at 75 ℃ in the surfactant sodium dodecyl-benzene-sulfonate. To verify the phase structure and morphology of the composite, X-ray diffraction, scanning and transmission electron microscopy, scanning tunneling electron microscopy, and Raman spectroscopy were employed. Room temperature data of magnetization versus magnetic field showed that the saturation magnetization MS=58.6 emu/gm for pristine Fe3O4 increased to MS=158.4 emu/gm for a 1:1 composite of Fe3O4 to MLG. These results lead to induced MS=253 emu/gm in MLG resulting from its proximity to Fe3O4. Similar experiments on Fe3O4 to single walled carbon nanotubes (SWNT) composite did not show any induced magnetism in SWNT. [ABSTRACT FROM AUTHOR]

Synthesis and nature of magnetism in ZnMnO3 nanoparticles with cubic spinel structure (a = 8.369 Å and size D ≃ 25 nm) are reported. Magnetization M vs. H and M vs. T data yield ferrimagnetism with TN ≃ 20 K, μ/Mn = 4.46 μB, MS ≃ 18.5 emu/g, and a transition at TS ≃ 7 K. For T < TN, coercivity and exchange-bias approach zero at TN with anomaly at TS. Using magnetic data and simulations, structure of [Zn2+][1/3]O11/3 with antiparallel moments of Mn4+ and Mn3+ is proposed. [ABSTRACT FROM AUTHOR]

With the discovery of magnetic ordering in RbMnF3, this unique antiferromagnetic system was recognized as a prime case for a test of conventional spin-wave theory (CSWT) because of its negligibly small anisotropy and its simple, cubic structure. CSWT predicts a simple T2 power-law fall-off of the sublattice magnetization. Yet to this day, no stringent tests have been made of this prediction. Seiden [(Phys. Lett. 28 A, 239 (1968)] deduced a T3 low-temperature behavior on the basis of antiferromagnetic resonance measurements, concluding that CSWT was not supported. We have recently carried out neutron scattering measurements of both single-crystal and powdered samples of RbMnF3 in order to test for CSWT, Seiden's result, and two other more recent semiempirical spin-wave schemes, and we present an analysis of the results. Measurements in the critical regime gave values of the critical exponent β and of TN that are in agreement with previous measurements. [ABSTRACT FROM AUTHOR]

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.)

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.

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.

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.

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.

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.

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.