Kinds Of Magnetic Interactions Research Articles

Electronic comprehension of exchange bias effect in Sr2CoRuO6−δ thin-film

Sr2CoRuO6 in its bulk form shows spin glass behavior with a transition temperature of 95 K, and in its epitaxial thin film, it shows similar behavior with a transition temperature of 135 K. We have studied the structural, electronic, and magnetic properties of a polycrystalline thin film of oxygen-deficient Sr2CoRuO6−δ (SCRO), which shows ferrimagnetic or glassy behavior up to room temperature. The presence of oxygen deficiency causes multivalent cations Co3+ and Co2+ and Ru4+ and Ru5+, which introduces various kinds of magnetic interactions between Co3+–O–Co2+, Co3+–O–Ru4+, Co2+–O–Ru4+, Co3+–O–Ru5+, and Co2+–O–Ru5+ exchange paths, producing unusual exchange bias effects in the single layer thin film of SCRO. The interionic charge transfer between Co and Ru ions as a result of the negative charge transfer energy of the system helps in visualizing the unconventional exchange bias effect in the system.

Coordination polymers containing a pyrazole-based ligand and 4,4′-bipyridine as a spacer: enhancing the family of nonzero-dimensional compounds featuring single-ion magnetic behavior

Two coordination polymers with molecular formula 1∞[M(L)2(4,4′-bipy)(H2O)2], where M stands for CoII (1) or CuII, (2), and L = 5-amino-1-phenyl-1H-pyrazole-4-carboxylate ligand were obtained by slow solvent diffusion and characterized by spectroscopic techniques, single crystal and powder X-ray diffraction, magnetic measurements, and DFT calculations. Magnetic studies carried out for complex 1 showed the key role played by the zero-field splitting and the experimental fit parameters were correlated to CASSCF calculations. Moreover, AC magnetic measurements for 1 revealed a field-induced slow relaxation of the magnetization and a single-ion magnet behavior. For the copper-containing polymer, two kinds of magnetic interactions were observed in the magnetic data and confirmed by using broken-symmetry DFT calculations: (i) ferromagnetic interchain coupling mediated by the hydrogen-bonds and (ii) antiferromagnetic intrachain interaction through the 4,4′-bipy ligand.

Nano-structured (Mo,Ti)C-C-Ni magnetic powder

Different kinds of structural and magnetic phases have been found in the investigated compounds, e.g. (Mo, Ti)C, C, Ni. It was found that such different phases create different kinds of magnetic interactions, from paramagnetic, antiferromagnetic up to superparamagnetic. Significant magnetic anisotropy has been revealed for low temperatures, which lowers with temperature increase. Moreover, non-usual increasing of the magnetization as a function of temperature was observed. It suggests, that overall long-range AFM interaction may be responsible for the magnetic properties.

Monte Carlo and Experimental Magnetic Studies of Molecular Spintronics Devices

Molecule-based spintronics devices (MSDs) are highly promising candidates for discovering advanced logic and memory computer units. An advanced MSD will require the placement of paramagnetic molecules between the two ferromagnetic (FM) electrodes. Due to extreme fabrication challenges, only a couple of experimental studies could be performed to understand the effect of magnetic molecules on the overall magnetic and transport properties of MSDs. To date, theoretical studies mainly focused on charge and spin transport aspects of MSDs; there is a dearth of knowledge about the effect of magnetic molecules on the magnetic properties of MSDs. This paper investigates the effect of magnetic molecules, with a net spin, on the magnetic properties of 2D MSDs via Monte Carlo (MC) simulations. Our MC simulations encompass a wide range of MSDs that can be realized by establishing different kinds of magnetic interactions between molecules and FM electrodes at different temperatures. The MC simulations show that ambient thermal energy strongly influenced the molecular coupling effect on the MSD. We studied the nature and strength of molecule couplings (FM and antiferromagnetic) with the two electrodes on the magnetization, specific heat and magnetic susceptibility of MSDs. For the case when the nature of molecule interaction was FM with one electrode and antiferromagnetic with another electrode the overall magnetization shifted toward zero. In this case, the effect of molecules was also a strong function of the nature and strength of direct coupling between FM electrodes. In the case when molecules make opposite magnetic couplings with the two FM electrodes, the MSD model used for MC studies resembled with the magnetic tunnel junction based MSD. The experimental magnetic studies on these devices are in agreement with our theoretical MC simulations results. Our MC simulations will enable the fundamental understanding and designing of a wide range of novel spintronics devices utilizing a variety of molecules, nanoclusters and quantum dots as the device elements.

Magnetic properties of co-modified Fe,N-TiO2 nanocomposites

Abstract Iron and nitrogen co-modified titanium dioxide nanocomposites, nFe,N-TiO2 (where n = 1, 5 and 10 wt% of Fe), were investigated by detailed dc susceptibility and magnetization measurements. Different kinds of magnetic interactions were evidenced depending essentially on iron loading of TiO2. The coexistence of superparamagnetic, paramagnetic and ferromagnetic phases was identified at high temperatures. Strong antiferromagnetic interactions were observed below 50 K, where some part of the nanocomposite entered into a long range antiferromagnetic ordering. Antiferromagnetic interactions were attributed to the magnetic agglomerates of iron-based and trivalent iron ions in FeTiO3 phase,whereas ferromagnetic interactions stemmed from the F-center mediated bound magnetic polarons.

Weak ferromagnetic component on the bulk ZnFe2O4 compound

Magnetization data on the bulk ZnFe2O4 antiferromagnetic compound (TN≈10K) obtained via solid state reaction at different synthesis temperatures show one weak ferromagnetic component at room temperature. We have related it with the cationic disorder effect present on spinel structure of our bulk samples which comes from the magnetic interaction between iron ions sit on both octahedral and tetrahedral sites. The magnetization measurements show to all samples a clear peak around 10K consistent with the antiferromagnetic phase transition. On the other hand, after extracted the paramagnetic component, the hysteresis loops measured at room temperature display one weak ferromagnetic component. Once the T-dependence of magnetization does not fit to a Curie–Weiss law to temperatures well above the magnetic transition we have used a combination of the Curie–Weiss law (paramagnetic spins) and a typical temperature dependence of M0, M0(T)=M0(0)[1−(T/TC)2]0.5 (ordered ferromagnetic spins). We note an increase of the M0(0) as function of the synthesis temperature. This reinforce our supposition of a cationic disorder effect driving the system to present two kinds of magnetic interactions between iron ions on A and B sites.

Magnetic Properties of KGd(WO4)2 Single Crystal Studied by EPR Spectroscopy

Magnetic properties of magnetically concentrated KGd(WO4)2 single crystal are studied using EPR spectroscopy. The EPR spectra are broad and have a complex shape, showing contributions of a few gadolinium centers. Temperature dependence of the total intensity of the EPR spectra and the inverse of the total intensity reveal two temperatures when the behavior of the total intensity suddenly changes, first one at 66.8 ± 3.3 K and the second one at 9.9 ± 2.8 K. Detailed analysis of this dependence suggests the presence of different magnetic systems of the Gd3+ ions. The EPR spectra were described by the spin Hamiltonian of monoclinic symmetry with electron spin S = 7/2, for which all g-matrix components and fine-structure parameters have been determined using EPR-NMR program. Raman spectra measured at low temperatures do not differ significantly from the one measured at room temperature. The analysis has given a deeper insight into different kinds of magnetic interactions between paramagnetic Gd3+ centers in KGd(WO4)2 single crystal.

Non-equilibrium magnetic interactions in strongly correlated systems

We formulate a low-energy theory for the magnetic interactions between electrons in the multi-band Hubbard model under non-equilibrium conditions determined by an external time-dependent electric field which simulates laser-induced spin dynamics. We derive expressions for dynamical exchange parameters in terms of non-equilibrium electronic Green functions and self-energies, which can be computed, e.g., with the methods of time-dependent dynamical mean-field theory. Moreover, we find that a correct description of the system requires, in addition to exchange, a new kind of magnetic interaction, that we name twist exchange, which formally resembles Dzyaloshinskii–Moriya coupling, but is not due to spin–orbit, and is actually due to an effective three-spin interaction. Our theory allows the evaluation of the related time-dependent parameters as well.

A magnetic communication scenario for hot Jupiters

The observations of enhanced chromospheric activity on HD 179949 as well as on ν And with the same periods as their close-in planets seem to indicate some kind of magnetic interaction between star and planet. A constraint to any possible model are the large phase angles of 60° and 169°, respectively. We present a simple model, which is based on the propagation of Alfven waves within the stellar wind flow relative to the planet and which can meet this restriction. In the solar system such a model is successfully used to explain the current system between lo and Jupiter.

Symmetry and Bonding Interactions in [Cu2Cl6]? Complexes

Two kinds of magnetic interactions are experimentally reported in [Cu 2 Cl 6 ] - complexes, namely ferromagnetic and antiferromagnetic ones. Symmetry related magnetic interactions in these complexes have been considered. First we defined the local symmetry properties of the molecule and then we determined symmetry adapted molecular orbitals. The bonding orbitals among two Cu atoms in [Cu 2 Cl 6 ] - complexes seem to be σ orbitals. However, the structure of these molecules indicates that π bonds must exist in these molecules.

Magnetic and transport properties of La 0.7Cd 0.3(Mn 0.9TM 0.1)O 3 transition metal doped manganites

In this work we present structural and magnetic properties of La 0.7Cd 0.3Mn 0.9TM 0.1O 3 (TM=Fe, Co, Ni) manganites. Samples were prepared by the sol–gel low temperature method. Preliminary room temperature structural characterization of these compounds shows a mixture of rhombohedral (R3̄c) and orthorhombic (Pnma) phases. The low value of the tolerance factor already indicates a distorted structure of the perovskite cell. Different kinds of magnetic interactions have been observed as the doping TM element is changed. Thus, respect to the undoped La 0.7Cd 0.3MnO 3 composition, the Curie temperature decreases for the Fe doped sample, but progressively increases as Mn ions are substituted by Co or Ni, respectively. The measured low temperature magnetic moment values are interpreted in terms of ferro- (for the Co and Ni doped samples) or antiferromagnetic (for the Fe doped sample) TM 3+-Mn 3+/Mn 4+ interactions. Despite their ferromagnetic character, all compositions show insulating behaviour in the whole temperature range studied.

Magnetic properties of iron-doped channels in H-Nb2O5

H-Nb2O5 (Nb28O70) is a semiconductor whose structure is built of NbO6 octahedra, which share corners and edges to form blocks parallel to the basal ac plane of the structure. One unit cell contains two blocks of 3 × 4 and 3 × 5 octahedra displaced by 1/2 b-axis spacing, besides one further Nb atom located in tetrahedrally coordinated sites along channels parallel to the b axis. Such channels contain octahedral interstices which are the preferential sites for point defect segregation in this structure. The possibility of using the channels as a framework for obtaining oriented spin arrays has never been explored in the literature. To investigate which kind of magnetic interaction would arise we manufactured a sample of H-Nb2O5 containing enough Fe to fill part of the octahedral interstices in the channels and measured the ac susceptibility response. The results were consistent with the formation of linear chains of spins, with variable coupling constants along the chains. The variable coupling can be understood as a consequence of the influence of the large number of possible arrangements of Nb and Fe atoms along the channels upon the sign and magnitude of superexchange interactions mediated by the oxygen atoms.

Crystal Structures of 4-(4-Halobenzylideneamino)-TEMPO Radicals Showing Magnetic Interactions

X-ray crystal structure analyses were performed on 4-(4-halo-benzylidene-amino)-TEMPO radicals, as well as other 4-Ar-CH=N-TEMPO radicals (Ar = 4-Ph-Ph, 4-Py, Ph, 4-MeS-Ph, 3-Py and 4-Me-Ph), at room temperature. Some of these crystals have been revealed to show intermolecular ferromagnetic interactions at an extremely low temperature. X-ray studies revealed that the crystals of the 4-I-Ph derivative showed two modifications; one showed a ferromagnetic transition and the other showed an antiferromagnetic interaction. Structural features of these TEMPO crystals are mainly classified to four groups: 1) structures of Cl-Ph, I-Ph and Ph-Ph derivatives which show a ferromagnetic transition, 2) Br-Ph and 4-Py derivatives with a ferromagnetic interaction, 3) Ph, 4-MeS-Ph, 3-Py, 4-Me-Ph derivatives showing different kinds of magnetic interactions, and 4) others including antiferromagnetic F-Ph and I-Ph derivatives.

Paramagnetic susceptibility simulations from crystal-field effects on rare-earth double molybdate and tungstate

Magnetic susceptibilities of polycrystalline samples of two series of double rare-earth molybdate and tungstate compounds, (RE = rare earth, X = Mo or W), with scheelite-type structure, space group (No 88), where RE atoms adopt point symmetry, have been measured in the temperature range 1.7 - 400 K. Using the wavefunctions and energy levels derived from standard free-ion and crystal-field parameters deduced from the analysis of the optical spectra of some selected (Pr, Nd and Eu) compounds, a systematic calculation of the temperature-dependent paramagnetic susceptibility, for all rare-earth configurations on the two series, has been carried out according to the Van Vleck formula. Very good agreements with experimental data are found over the whole temperature range. The standard crystal-field treatment of ions is shown to explain the magnetic properties of these compounds, for which no kind of magnetic interaction among the rare-earth ions has been detected.

Ordered magnetic frustration: VI. Crystal and magnetic structures of the inverse weberites ZnFeF 5(H 2O) 2 and MnFeF 5(H 2O) 2 at 1.5 K from powder neutron diffraction

The nuclear and the magnetic structures of the ferrimagnetic ( T c = 39.5(2) K) MnFeF 5(H 2O) 2 and of the antiferromagnetic ( T N = 9(2) K) ZnFeF 5(H 2O) 2 inverse weberites were solved by neutron powder diffraction at 50 and 1.5 K, respectively. The room temperature structures are confirmed and hydrogen atoms are located. Below the magnetic ordering temperature, the magnetic and nuclear cells are identical. For MnFeF 5(H 2O) 2 (space group Imm2), the Bertaut's modes are +F x , −G z , and −F x , +F y , −G z for Fe 3+ and Mn 2+ spins, respectively, with corresponding moments of 3.43(9) and 4.93(11) μ B ( R mag = 0.087). For ZnFeF 5(H 2O) 2 (space group Imm2), the Bertaut's mode is G y for Fe 3+ spins, the moments being 3.78(5) μ B ( R mag = 0.066). These results, which show the influence of the existence of a topologically frustrating triangular cationic subnetwork on the magnetic behavior of compounds, are compared to those previously obtained on Fe 2+Fe 3+F 5(H 2O) 2, which cumulate the different parameters that govern frustrated behavior: triangular network, different kinds of magnetic interactions, and anisotropy.

Some Experiments on Synthetic Titanomagnetites

Summary A range of synthetic samples of the magnetite-ulvospinel series has been made by the usual sintering technique. These samples were subjected to oxidation, and subsequent annealing treatment in vacuum. Magnetic measurements and petrological observations were made at each stage in the treatment. It is concluded that the magnetic stability of the samples is greatly increased as a result of oxidation; the TRM also increases by a considerable amount. Some of the oxidized and annealed samples behave in an unusual manner in weak magnetic field experiments, and seem to show a novel kind of magnetic interaction.

Theory of the Microwave Zeeman Effect in Atomic Oxygen

Slight deviations of the coefficient of the linear Zeeman term from the elementary Land\'e value arise from the following effects: ($a$) small departures from Russell-Saunders (R-S) coupling, ($b$) the motion of the nucleus, ($c$) relativity corrections, ($d$) interplay between the magnetic field and various kinds of magnetic interactions within the atom, and ($e$) the Schwinger electro-dynamical corrections. In the present paper an effort is made to estimate the magnitude of the effects ($a$), ($b$), ($c$), ($d$) with the goal of examining whether the residual discrepancy between Rawson and Beringer's measurements on oxygen and the ideal Land\'e value is in accord with Schwinger's formula for ($e$).The effect ($d$) may be further divided into modulation by the magnetic field, or Larmor precession, of (${d}_{1}$) ordinary spin-orbit, (${d}_{2}$) spin-other-orbit, and (${d}_{3}$) orbit-orbit interaction. The theory for $c$ and ${d}_{1}$ has already been developed by Margenau and Breit, and ${d}_{2}$ to a certain extent by Lamb, while that for $b$ was first given by Phillips. The corrections ($d$) can in each case be obtained by substituting $\mathrm{p}+\frac{e\mathrm{A}}{c}$ for p in the corresponding magnetic interaction terms in the Pauli two-component Hamiltonian function, but can also be derived more fundamentally from the four-component Dirac equation. From the standpoint of the Dirac equation, the segregation of ($c$) from other magnetic effects is rather artificial, but ($c$) has the simple physical interpretation that it is tantamount to substituting the transverse mass for the rest mass in the ordinary Zeeman energy.The numerical estimate of effects $(b)\ensuremath{-}(d)$ requires knowing the wave functions in some detail. Certain rather crude approximations are made in the present paper, including omission of exchange terms in some places. However, the agreement between the calculated and observed Zeeman coefficients after all the corrections ($a\ensuremath{-}e$) are included is gratifying.