Types Of Magnetic Behavior Research Articles

Structural, morphological and magnetic properties investigation of magnetically separable mesoporous carbon

This paper reports on the preparation of nanocomposites containing mesoporous carbon with different molar ratios of Ni or CoFe2O4 nanoparticles as magnetically separable absorbents by facile, reproducible and economical processes including self-assembly soft template hydrothermal route and Pechini-type sol-gel techniques. Accordingly, structural, morphological and magnetic properties of the samples were studied using XRD, FT-IR, FE-SEM, HR-TEM, N2 adsorption-desorption and VSM methods. Based on the VSM results, two different types of magnetic behavior were observed. Composites containing nickel had typical S-shaped hysteresis curves with a very low coercivity (Hc ≈ 84, 97 Oe) and retentivity (Mr ≈ 1.1, 2.4 emu/g), as compared to their relatively high saturation magnetization value (Ms ≈ 3.9, 8.6 emu/g), while the other samples were ferromagnetic. The M − H curves have also revealed that saturation and remnant magnetization, as well as coercivity, were increased by enhancing the magnetic phase content in all nanocomposites. Also, the MC-Ni/CFO nanocomposites performance as the magnetically separable adsorbents for vitamin B12 adsorption was evaluated. The MC-5CFO adsorbent illustrated higher adsorption capacity (325.66 mg/g) than MC-2Ni (139.25 mg/g) in 250 ppm due to the higher BET surface area (589 m2/g) and pore volume (0.71 cm3/g).

Electronic structures and magnetic properties in transition metal adsorbed gt-C3N4 monolayer

Abstract Basing on ab initio calculations, we investigate the electronic structures and magnetic properties of triazine-based graphitic carbon nitride (gt-C3N4) sheets with adsorbed transition metals (TM). TM atoms energetically prefer to be adsorbed on the vacancy site. Adsorptions lead to magnetic moments of 1.0, 2.0, 3.0, 3.0, 2.0, and 3.0 μB for Sc, Ti, V, Mn, Fe, and Co, respectively, which originate from the cooperation between ligand field theory and Hund’s rule. Adsorptions result in different types of magnetic behavior that vary with TM. The system remains semiconducting but with reduced band-gap upon the adsorption of Cr or Ni atom. The adsorption of V and Co atoms can transform semiconducting gt-C3N4 into magnetic metallicity and half metallicity, respectively, with an estimated Curie temperature (TC) above room temperature. Sc, Ti, Fe, and Mn adsorption induce anti-ferromagnetism in the host gt-C3N4. These findings indicate adsorptions of TM lead to various magnetic characters that has potential application in future spintronics.

Signatures of consolidated superparamagnetic and spin-glass behavior in magnetite-silver core-shell nanoparticles.

A detailed investigation of magnetization relaxation for silver-coated magnetite nanostructures with three different types of magnetic behavior in a single particle is presented. Magnetite nanoparticles of diameter ∼6.5 nm synthesized via single-phase emulsion were further coated with a silver shell of thickness ∼2 nm. The synthesized nanoparticles are found to be efficiently photoluminescent. The coating of silver generates a magnetically disordered spin layer at the interface of the magnetic core and the non-magnetic shell. This intermediate layer plays a significant role in the dynamical magnetic response of nanoparticles under an external magnetic field. We present detailed magnetic measurements such as field- and temperature-dependent dc magnetization with zero-field-cooled and field-cooled protocols, ac susceptibility and time decay of magnetization relaxation along with their analysis using various formalisms viz. Néel-Arrhenius, Vogel-Fulcher and power law models. The relaxation analysis suggests the consolidated presence of two characteristic relaxation times corresponding to the superparamagnetic and spin-glass behavior of silver-coated magnetite nanoparticles.

Influence of Fe doping on magnetic properties of ZrO2 nanocrystals

The aim of the present work is to study the magnetic properties of ZrO2(Fe) nanocrystals prepared by the wet chemistry method. The microwave assisted hydrothermal synthesis was used. The detailed structural characterization was performed by means of X-ray diffraction and TEM studies. 57Fe Mössbauer spectra were recorded at room temperature for all samples. The isomer shift and quadrupole splitting indicate the presence of Fe3+ ions. The systematic measurements of AC magnetic susceptibility up to 350K and magnetization as a function of magnetic field (up to 9T) and temperature were performed. Depending on the nominal concentration of magnetic dopant different types of magnetic behavior, were observed.

The Nature of Spin Crossover and Coordination Core Distortion in a Family of Binuclear Iron(II) Complexes with Bipyridyl‐Like Bridging Ligands

AbstractThe synthesis and characterization of two new binuclear compounds [{Fe(dpia)(NCS)2}2(bpac)]·nCH3OH [n = 0 (1) and 2 (2), dpia = bis(2‐picolyl)amine, bpac = 1,2‐bis(4‐pyridyl)ethyne] are reported. The magnetic susceptibility measurements of the compounds revealed different types of magnetic behavior. Complex 1 displays a two‐step spin crossover (SCO) that suggests the occurrence of a mixed [HS–LS] (HS = high spin, LS = low spin) pair at the plateau temperature (145 K), at which about 50 % of the complexes undergo a thermal spin conversion. The high‐temperature step is very gradual, whereas the low‐temperature step shows a first‐order spin transition with a hysteresis width equal to 17 K. Compound 2 manifests a relatively abrupt one‐step spin change with a narrow hysteresis of 4 K. The single‐crystal X‐ray structure of 1 was solved for the [HS–HS] complex at room temperature. Compound 2 was structurally characterized in both [HS–HS] and [LS–LS] spin states at 290 and 110 K. The magnetic and structural characteristics of 1 and 2 were compared with previously reported related binuclear compounds with 4,4′‐bipyridine and 1,2‐bis(4‐pyridyl)ethene spacer ligands. This analysis confirms a recently proposed idea about the key role of the [FeN6] core structural distortions, which are caused by crystal packing and strain effects of terminal and/or bridging ligands, in the spin‐crossover behavior of binuclear complexes. This study also revealed the predominant role of inter‐ vs. intramolecular interactions in the spin transition cooperativity.

Magnetic properties of nanocrystalline ZnO doped with MnO and CoO

We have studied the magnetic properties of ZnO nanocrystals doped with MnO and CoO in the wide range of magnetic dopant (from 5 to 95 wt. %), synthetized by wet chemical method. The samples were characterized by means of XRD and micro-Raman spectroscopy. The results of systematic measurements of magnetic susceptibility as a function of temperature and frequency as well as SQUID magnetization are presented. We observed different types of magnetic behavior. ZnO nanocrystals doped with CoO demonstrate Curie-Weiss behavior at higher temperatures. For samples doped with MnO, we observed the superparamagnetism above the blocking temperature.

Synthesis by Wet Chemical Method and Characterization of Nanocrystalline ZnO Doped with Fe2O3

Nanocrystalline samples of ZnO doped with Fe2O3 were synthetized by wet chemical method. The series of ZnO nanosized samples in the wide range of Fe2O3 concentration (from 5 wt.% to 95 wt.%) was prepared by precipitation from nitrate solutions using ammonia. The phase composition of the samples was determined using X-ray diffraction measurements. The phases of hexagonal ZnO, and/or rhombohedric Fe2O3, and/or ZnFe2O4 were identified. The mean crystalline size of nanocrystals, determined with the use of Scherrer’s formula, varied from 8 to 52 nm. The preliminary micro-Raman spectroscopy measurements were performed. The observed features are typical of Fe doped ZnO nanoparticles. The magnetic measurements revealed the presence of different types of magnetic behavior. For samples with high Fe2O3 contents (above 70 wt.%) the ferromagnetic ordering was observed at room temperature. For samples with lower Fe2O3 contents we observed the phenomenon of superparamagnetism above the blocking temperature.

Correlated electron systems on the Apollonian network

Strongly correlated electrons on an Apollonian network are studied using the Hubbard model. Ground-state and thermodynamic properties, including specific heat, magnetic susceptibility, spin-spin correlation function, double occupancy and one-electron transfer, are evaluated applying direct diagonalization and quantum Monte Carlo. The results support several types of magnetic behavior. In the strong-coupling limit, the quantum anisotropic spin 1/2 Heisenberg model is used and the phase diagram is discussed using the renormalization group method. For ferromagnetic coupling, we always observe the existence of long-range order. For antiferromagnetic coupling, we find a paramagnetic phase for all finite temperatures.

Structural and magnetic instabilities in ultrathin Fe-rich alloy films on Cu(100)

A well-known property of Fe/Cu(100) films is the existence of live surface layers above ∼4 ML (monolayer). This is correlated with structural changes as seen with low electron energy diffraction. Up to ∼4 ML a (n×1) diffraction pattern is observed with n∼5. This changes into a pattern with a (2 X I ) symmetry for thicker films. We have studied the evolution of the structural and magnetic properties of Fe x Ni 1 - x and Fe x Mn 1 - x /Cu(100) films with Fe contents above 80%. The magnetic studies indicate two types of magnetic behavior. Initially the films are uniformly magnetized as judged from the thickness dependence of the Kerr signal. In this thickness regime the (n X 1) diffraction pattern shows a thickness dependence of n. For all samples we find that n varies linearly from 4-6 in the thickness regime 2-4 ML. The uniformly magnetized state is followed by a phase with constant Kerr intensity. This change in the magnetic properties is accompanied by a change in the diffraction pattern which becomes either (2 X 1) or p(I X 1). Further, we find the easy axis is normal to the surface for the uniformly magnetized films and magnetic live surface layers. We discuss our results in the context of a nanomartensitic bcc phase recently observed for Fe/Cu(100).

Paleomagnetism of baked sedimentary rocks in the Newark and Culpeper basins: Evidence for the J1 cusp and significant Late Triassic apparent polar wander from the Mesozoic basins of North America

A paleomagnetic study of 14 sites in the baked sedimentary rocks of the Newark basin Passaic Formation in southeastern Pennsylvania reveals two types of magnetic behavior. Dark gray‐colored, baked sedimentary rocks have peak unblocking temperatures of 640°C, high magnetic intensities, and shallow, normal polarity, northeasterly directions. Light gray‐colored rocks have peak unblocking temperatures of less than 580°C, low magnetic intensities, and intermediate inclination, normal polarity, northwesterly directions. The low unblocking temperature magnetizations are secondary magnetizations which have declinations similar to but are shallower than the B remagnetization observed by Witte and Kent (1991) throughout the Newark basin. The discrepancy may be due to “underprinting” by an unresolved primary magnetization. The low unblocking temperature magnetization was probably acquired by growth of secondary magnetite during a hydrothermal event, as postulated by Sutter (1988), based on geochronologic data. The high unblocking temperature magnetization is significantly prefolding. Both the low‐peak unblocking temperature magnetization and the high‐peak unblocking temperature magnetization suggest a 15° counterclockwise block rotation of the Sassamansville syncline. If this rotation is removed from the high unblocking temperature sites collected around the fold, a stronger passage of the fold test results. Six sites were also collected from baked sediments and one site from diabase in northern Virginia's Culpeper basin, since Sutter's geochronological work indicated that the intrusives in the Culpeper basin are coeval to the Newark basin intrusives. Virtual geomagnetic poles (VGPs), based on the tilt‐corrected, high‐temperature Newark basin magnetizations, were compared with the VGPs calculated from the site means of a high‐temperature magnetization isolated from baked sedimentary rocks in the Culpeper basin and to the magnetizations reported by Raymond (1982) from dikes and sills. In this comparison the in situ Culpeper poles agreed with the prefolding Newark poles significantly better than the prefolding Culpeper poles. This result indicates that Culpeper intrusives erupted into already tilted sedimentary rocks. The paleomagnetic pole determined from the combined Culpeper baked sediments, dikes, and sills (in situ coordinates) and the Newark basin baked sediments (tilt‐corrected coordinates) lies at 60°N, 69°E and is of 201 Ma age. This latest Triassic/earliest Jurassic pole, when combined with the Newark basin Carnian results (Witte and Kent, 1989) and Norian results (Witte et al., 1991) corrected for a counterclockwise block rotation (Kodama et al., 1994), provides a record of significant polar wander from eastern North America's Mesozoic basins for the Late Triassic. This is consistent with observations made for a similar time period from rocks on the Colorado Plateau (Bazard and Butler, 1991). Comparison of the Newark/Culpeper pole to similar age poles from the Kayenta (Bazard and Butler, 1991) and Moenave Formations (Ekstrand and Butler, 1989) only requires small amounts (5°) of Colorado Plateau rotation. The pole also provides the first well‐dated evidence of the Jl cusp in North American apparent polar wander from rocks not located on the Colorado Plateau, thus giving strong support for the usefulness of paleomagnetic Euler pole analysis of apparent polar wander.

Magnetic properties of the lightly doped t-J model: A study through high-temperature expansions.

We develop high-temperature expansions for the complete q-dependent static structure factor of the two-dimensional t-J model for arbitrary parameter ratio t/J and particle density p. The analysis of the series reveals several different types of magnetic behavior. The spin-spin correlations are peaked at the antiferromagnetic vector (π,π) at half filling (p=1). For small t/J, these correlations stay commensurate even with moderate doping down to as low a temperature as is accessible to our extrapolations; they become incommensurate at large dopings at temperatures below J

Crystal growth and single-crystal physical properties of rare-earth-based chevrel phases REMo 6S 8 (RE = Sm, Dy, Tm).

Single crystals of rare-earth molybdenum sulfides REMo 6S 8 (RE= Sm, Dy, Tm) have been obtained by high temperature melting. Transport, magnetic and superconducting properties are presented. Three types of magnetic behaviour are observed: a non-magnetic singlet ground state of Tm 3+ in TmMo 6S 8, a VanVleck paramagnetism at high temperatures in SmMo 6S 8 and a paramagnetic state with crystal field effects in DyMo 6S 8.

Low-temperature dynamics of local-moment systems investigated by thermal cycling methods

We report studies of the low-temperature dynamics of several dilute alloy systems in which local moments are present, using various thermal-cycling nuclear orientation methods. Determinations of nuclear spin-lattice relaxation over a wide concentration range in the giant-moment alloys CoPd illustrate the various types of magnetic behavior in this system. Experiments on dilute TbAu show evidence of clustering and impurity-impurity interactions. Strong local moments are formed on Mn in the weak ferromagnet ZrZn2, but the relaxation behaves as in a paramagnetic alloy.

New 1-D magnetic systems in fluorides with the usovite-type structure

Abstract New compounds with the usovite-type structure have been prepared which exhibit different types of magnetic behavior depending on the magnetic ions involved. In BaMnAlF7 and BaMnGaF7 antiferromagnetic chains are observed. For Ba2CaCoFe2F14 and Ba2CaMnFe2F14 the magnetic behavior is characteristic of ferrimagnetic chains. For the cobalt compound a magnetic transition with applied field has been observed below 30 K. For Ba2CaCuFe2F14 the magnetic properties have been analyzed in terms of isolated Fe3+ -Cu2+ -Fe3+ trimeric units.

An Exactly Soluble Model of Singlet‐Ground‐State Ferromagnetism

AbstractA system of “atoms”, each one of which can be in one of two spin states, is considered. On the assumption that in one of the two atomic states a ferromagnetic interaction exists, the magnetic properties of the system are investigated. Various types of magnetic behaviour and phase transitions are found. Over a certain reasonable range of model parameters heat magnetization is obtained.

A model for the thermodynamic properties of metallic rare earth systems with an unstable valence

Rare earth compounds and alloys were regarded for many years as classic examples of ionic magnetism in a solid. Due to the limited spatial extent of the 4f wave functions, the 4f electrons do not significantly participate in the chemical bonding, and hence retain most of their ionic character during the transition from a gas to a solid. However, recent experimental evidence on several metallic rare earth systems indicated an apparent loss of the ionic magnetic moment. Extensive measurements on these systems of the magnetic susceptibility, lattice constant, Mossbauer isomer shift, x-ray photoelectron spectrum, and heat capacity can be qualitatively understood if one postulates (as was first done by Maple and Wohlleben using a model due to Hirst) that the rare earth ion fluctuates between two ionic configurations (valence states) which differ in occupation number by one electron (4f n , 4fn−1 5d1). We propose to quantify this simple idea by assigning each valence configuration a finite lifetime atT=0. The two lifetimes τ n and τ n−1 are converted to “bands” with widthsh/τ n andh/τ n−1 . The states in each “band,” however, are forced to retain the ionic properties as determined from Hund's rules. The temperature-dependent contribution of the 4f shell to the magnetic susceptibility, heat capacity, and thermal expansion coefficient is then numerically computed using Fermi-Dirac statistics. By varying τ n and τ n−1 it is possible to quantitatively describe “different” types of magnetic behavior: integral valence (τ n =∞, τ n−1 =h/Δ), configuration crossover (τ n =τ n−1 ), and Kondo phenomena (τ n >τ n−1 ). The results of the model are compared to three well-studied rate earth systems with unstable valence: YbAl 3 , CePd 3 , and (LaCe)Al 2 .

A determination of paleomagnetic field intensity using submarine basalts drilled near the Mid-Atlantic Ridge

Paleomagnetic field intensities have been determined by a modified Thellier heating method for five basalts from a collection of 23 rocks drilled at sites 332 and 335 of Deep-Sea Drilling Project leg 37 in the Americas plate just west of the mid-Atlantic ridge at 37°N. Samples from hole 332B were from depths of 220–555 m in oceanic layer 2. Natural remanent magnetizations (NRM's) of these rocks remained fairly stable during alternating field demagnetization to 1000 Oe, and 6 of 7 tested were directionally stable during thermal demagnetization to 250°C. NRM intensities were low in relation to submarine basalts sampled elsewhere (0.5 to 4.5×10−3 emu cm−3 and a mean of 2.26×10−3 emu cm−3). Although there is a pronounced negative (linear) anomaly over the site, the NRM's are of mixed polarities. Inclinations are uniformly shallow, − 1–34°, and are much less than the dipole inclination of 50–55° at 37°N. Because of the low intensities, mixed polarities, and shallow inclinations of NRM, the integrated magnetic signal above the sequence is insufficient to explain the linear magnetic anomaly over site 332. The main anomaly source must be deeper than 600 m in layer 2 or, conceivably, in layer 3. Hole 335 samples (about 110-m basement penetration) had NRM's of similar intensity but with uniform negative polarity in accord with the sign of the sea surface anomaly and with the high inclinations (48–57°) expected for 37°N. Rock magnetic studies revealed two types of magnetic behavior. Type 1 rocks have a single low (150–200°C) Curie point and reversible thermal behavior, but they tend to be magnetically soft and viscous. Type 2 rocks have two Curie points. They are magnetically hard and nonviscous, but they change irreversibly when they are heated (in air or vacuum) above 300°C. Both types are less than ideal material for paleointensity determination, since heatings are limited to the 20–200°C range. As a result, only four or five points could be obtained for each Thellier plot, and because less than 20% of the NRM was demagnetized at 200°C in four of the five samples successfully studied, the scatter is greater than it would be in similar studies of continental rocks. The paleofield intensities indicated are 0.1−0.45 Oe at 3.5±0.1 m.y. B. P. (site 332) and ≈0.3 Oe at 10.5–16.5 m.y. B. P. (site 335). Although these paleointensities are apparently reliable (within broad confidence limits), some may be low in comparison with the present field because of viscous decay of the NRM, which may be undetectable when heatings are limited to 200°C. In support of this idea there is a correlation in our results between unstable behavior during a 2-month storage test of NRM and very low apparent paleointensity. Viscous effects may be partly responsible for high apparent paleointensity values in rocks magnetized during a normal polarity epoch (e.g., rocks from the median valley of the mid-Atlantic ridge) and for low apparent paleointensities in rocks away from the ridge magnetized during reversed epochs or events.

Substituted phenols as ligands. Part II. Copper(II) complexes

Copper(II) complexes with the 2-methoxyphenolate ion, its 4-formyl-, 4-nitro-, and 4-formyl-6-methoxy-derivatives and the 2-ethoxy-4-formylphenolate ion are reported. Hydrated compounds with the formula Cu(ligand)2,-xH2O (where x= 2, 3, or 4) are generally obtained from aqueous solution which on dehydration yield the complexes Cu(ligand)2. The complexes possess a distorted octahedral stereochemistry with the exception of bis-(2-methoxyphenolato)copper(II), which has no hydrate, which may be a rare case of the CuO4 distorted tetrahedral chromophore. One isomeric form of bis(2-ethoxy-4-formylphenolato)copper(II) dihydrate may have a quasi-tetrahedral stereochemistry but could be six-co-ordinate with a rhombic perturbation. Bis(2-ethoxy-4-formylphenolato)copper(II) dihydrate has a tetragonal six-co-ordinate isomer. Both forms dehydrate to give six-co-ordinate products which are identical.Two types of magnetic behaviour are observed. The anhydrous complexes have subnormal room temperature moments arising from magnetic exchange. Two of them display Neel points and these results correspond to the expected behaviour for interacting dimeric aggregates. The others fit the lsing one-dimensional magnetic model in which the crystal consists of a number of infinite chains of interacting magnetic centres. The hydrates have normal magnetic moments suggesting magnetically isolated copper(II) ions.There is no conclusive evidence regarding the participation of the 2-alkoxy-group in co-ordination, however, complexes with no 2-substituent could not be prepared.

Magnetochemistry: Introductory lecture

The simple fundamentals of magnetic susceptibility and its determination are first summarised and the various types of magnetic behaviour indicated. The theoretical basis of magnetic susceptibility is outlined and paramagnetism is discussed in some more detail. The latter is divided into various types depending upon the multiplet separation and the strength of the electrical ligand field around the ion. The applications of magnetic susceptibility measurements to valency problems are then discussed, attention being drawn to the uncertainty existing when metal-metal interaction occurs. The relationship of susceptibility and bond type is discussed and the limitations are emphasised. The way in which paramagnetic measurements may be used to determine the stereochemistry of transition metal complexes is surveyed. In addition to a survey of the use of the number of unpaired d electrons for this purpose the way in which the deviation from the spin-only moment may be employed is also discussed. The importance of the Kotani theory in providing an understanding of strong field complexes in which the moment is less even than that expected from the Pauling theory is emphasiesed. Tables of the magnetic behaviour of spin free and spin paired complexes are provided.