Search

Experiments for vanadium dioxide show a magnetic transition characterized by a sharp variation in susceptibility associated with the metal-insulator transition at the temperature Tc. The sample is shown to be of Pauli paramagnetism above Tc but of anomalous paramagnetism below Tc. Considering co-contributions of Pauli paramagnetism of residual V4+ ions and Curie-like paramagnetism of V-V dimers, we propose a phenomenological expression for the temperature-dependent susceptibility below Tc, which yields an excellent agreement with the experimental data. The unusual temperature dependence of Curie-like susceptibility below Tc is explained to be due to the fact that every dimer is formed by spin paring at an angle θ close to 180° and hence has an effective spin expressed as Seff = cos (θ/2) which decreases with lowering temperature. The observed metal-insulator and magnetic transitions are argued to be due to a transition from the high-temperature Pauli paramagnetic state of V4+ ions to the low-temperature dimerized state. [ABSTRACT FROM AUTHOR]

The magnetic properties of 2H phase of MoS2 (2H-MoS2) and 1T phase of MoS2 (1T-MoS2) were investigated both experimentally and theoretically. Lithium (Li) intercalation method was used to prepare single-layer MoS2 sheets. It was found that pristine MoS2 (2H-MoS2) exhibited weak diamagnetism. After exfoliating by Li intercalation, the crystal structure transformed from 2H to 1T phase, and the magnetism was significantly enhanced from diamagnetism to paramagnetism accordingly. With further annealing in argon atmosphere, the 2H phase recovered gradually from 1T phase, and the magnetism decreased correspondingly. Using crystal field theory and combining the results of first principle calculation, we conclude that the enhanced magnetism can be attributed to the Mo atoms of 1T-MoS2. [ABSTRACT FROM AUTHOR]

We have studied the magnetization of vertically aligned graphene nanoflakes irradiated with nitrogen ions of 100 KeV energy and doses in the range 1011-1017 ions/cm2. The non-irradiated graphene nanoflakes show a paramagnetic contribution, which is increased progressively by ion irradiation at low doses up to 1015/cm2. However, further increase on implantation dose reduces the magnetic moment which coincides with the onset of amorphization as verified by both Raman and x-ray photoelectron spectroscopic data. Overall, our results demonstrate the absence of ferromagnetism on either implanted or unimplanted samples from room temperature down to a temperature of 5 K. [ABSTRACT FROM AUTHOR]

This letter reports that both ac susceptibility and electronic transport measurements of the multiferroic compound LuFe2O4 under pressure show that the transition temperature from the paramagnetic state to the ferrimagnetic state decreases with increasing pressure, indicating that the pressure favors the paramagnetic state and suppresses the ferrimagnetic state. Moreover, the minimum of resistivity changes under pressure, which decreases with increasing pressure, appears at the magnetic phase transition temperature. [ABSTRACT FROM AUTHOR]

ZnCoO:H nanocrystals are weak ferromagnetic at room temperature with a small coercivity and a small remanence, whereas ZnCoO nanocrystals are paramagnetic. The thermal irreversibility of zero-field cooling and field cooling magnetizations of ZnCoO:H nanocrystals corresponds to the existence of superparamagnetism due to the nanosize effect. X-ray photoelectron spectra show the incorporation of Co2+ ions inside the ZnO lattice without changing the wurtzite structure. Our data suggest that hydrogen can induce ferromagnetism in ZnCoO and that ferromagnetic ZnCoO:H crystals with small particle size can show the superparamagnetism. [ABSTRACT FROM AUTHOR]

Employing phase sensitive micro-Hall magnetometry at room temperature, we map the susceptibility of a single superparamagnetic bead, 1.2 μm in diameter, as a function of magnetic field. We find that the dependence can be explained by modeling the bead as an ensemble of noninteracting superparamagnetic nanoparticles with log-normal distribution of magnetic moments. We also discuss the effect of possible dipolar interactions between the nanoparticles on the obtained results. [ABSTRACT FROM AUTHOR]

The authors have investigated the structural and magnetic properties of CrN films grown on MgO(001) and sapphire(0001) by rf-plasma-assisted molecular beam epitaxy. CrN/MgO(001) exhibits a better epitaxial quality than CrN/sapphire(0001). The CrN/MgO film shows clear paramagnetic behavior at low temperatures, whereas CrN/sapphire exhibits a ferromagneticlike response with an order temperature above room temperature which resembles the magnetic behavior found in Cr-doped dilute magnetic semiconductors. Keeping in mind that bulk CrN exhibits antiferromagnetic behavior, the dramatically different magnetic behaviors found in epitaxial CrN films grown on MgO and sapphire demonstrate the importance of epitaxial constraints in determining their magnetic properties. [ABSTRACT FROM AUTHOR]

A 0.5% Al-doped Zn0.895Co0.100O polycrystalline powder was synthesized by the co-precipitation method. Raman spectroscopy revealed that divalent cobalt ions were substituted for Zn2+ ions into the ZnO matrix and that Al ions activate additional modes which are nonspecific to the dopant. These additional modes disappear after annealing at 1373 K for 1 h under Ar flow. We suggest that the electrical dopant becomes active in substitutional sites after annealing. Resistance measurements confirm that free carriers were created in our sample. Nevertheless, the sample shows the same magnetic properties: a mixture of paramagnetism and antiferromagnetism. [ABSTRACT FROM AUTHOR]

For phase-separated La0.275Pr0.35Ca0.375MnO3 manganite, a steplike charge-ordered antiferromagnetic-ferromagnetic transition was observed by field induction and accompanied by a sudden drop of resistivity. The results can be explained in terms of the spin reorientation in the antiferromagnetic (AFM) phase and simultaneous destruction of orbital ordering by a magnetic field. Combined with specific heat and magnetization measurements, the electronic state density at Fermi energy was greatly enhanced at 5 T, which shows the increase of carrier number due to delocalization effect, by analogy with the spin reorientation due to destruction of orbital ordering by magnetic field. The present results prove that the strong coupling among spin, charge, and orbital ordering would be the main cause of existing complex physical behavior at low temperature, which depends sensitively on the spin orientation of adjacent charge-ordered AFM domains and can be controlled by applied field. [ABSTRACT FROM AUTHOR]

Calculations of magnetization reversal mechanism and coercivity reduction in exchange coupled FePt/FeRh bilayers are presented. It is shown by comparison with atomistic model calculations that the use of a standard micromagnetic model leads to an underestimation of the exchange energy at the interface, leading to a reduced coercivity decrease for small interfacial exchange energy constant. This is due to the failure of the domain wall (DW) to penetrate the hard FePt phase in the micromagnetic calculations. A multiscale model is proposed based an atomic level simulation in the interface region coupled with a micromagnetic approach elsewhere. This leads to improved calculations of DW structures at the interface, allowing a detailed study of the magnetization reversal mechanism. The new approach predicts a saturation in the coercivity reduction as a function of interface exchange energy at 4% of the bulk value, which is associated with complete continuity of the DW across the interface. [ABSTRACT FROM AUTHOR]

Magnetic properties of the Sr-doped BaCoO3 are explained on the basis of ab initio calculations and the analysis of experimental literature. Formation of magnetic clusters bigger than in the parent compound and an increase in the blocking temperature are observed. Superparamagnetism remains at room temperature. The possibility of tuning the size and properties of the magnetic clusters with doping is explored. [ABSTRACT FROM AUTHOR]

We developed a macrospin model describing the storage layer magnetization dynamics under spin-transfer-torque (STT) in in-plane magnetized magnetic tunnel junctions comprising a perpendicular, out-of-plane magnetized, polarizer. Two regimes were observed in the storage layer magnetization dynamics under the influence of the two STT contributions originating from the perpendicular polarizer and in-plane reference layer: (i) a regime of steady precession under DC current when the STT from the perpendicular polarizer dominates and (ii) a regime of bipolar switching in a direction determined by the current direction when the STT from the in-plane reference layer dominates. [ABSTRACT FROM AUTHOR]