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Graphdiyne (GDY) was prepared by a cross-coupling reaction and its magnetic properties were studied. The results show that the as-prepared GDY is spin-half paramagnetism. GDY shows the increase in the spin density by annealing, and antiferromagnetism appears after annealing at 600°C. The density functional calculations show that (i) the hydroxyl groups on the chain of GDY sheet are the major magnetic sources, and (ii) these hydroxyl groups have the high barrier energy of 1.73 eV for migrating from the ring site to chain site, which can prevent the hydroxyl groups’ clustering and may favor the antiferromagnetism in the annealed GDY. [ABSTRACT FROM AUTHOR]

Nanoscale chiral skyrmions in noncentrosymmetric helimagnets are promising binary state variables in high-density, low-energy nonvolatile memory. Skyrmions are ubiquitous as an ordered, single-domain lattice phase, which makes it difficult to write information unless they are spatially broken up into smaller units, each representing a bit. Thus, the formation and manipulation of skyrmion lattice domains is a prerequisite for memory applications. Here, using an imaging technique based on resonant magnetic x-ray diffraction, we demonstrate the mapping and manipulation of skyrmion lattice domains in Cu2OSeO3. The material is particularly interesting for applications owing to its insulating nature, allowing for electric field-driven domain manipulation. [ABSTRACT FROM AUTHOR]

We have synthesized transparent, conducting, paramagnetic stannate thin films via rare-earth doping of BaSnO3. Gd3+ (4f7) substitution on the Ba2+ site results in optical transparency in the visible regime, low resistivities, and high electron mobilities, along with a significant magnetic moment. Pulsed laser deposition was used to stabilize epitaxial Ba0.96Gd0.04SnO3 thin films on (001) SrTiO3 substrates, and compared with Ba0.96La0.04SnO3 and undoped BaSnO3 thin films. Gd as well as La doping schemes result in electron mobilities at room temperature that exceed those of conventional complex oxides, with values as high as 60 cm²/V⋅s (n=2.5 x 1020cm-3) and 30 cm²/V⋅s (n=1x1020cm-3) for La and Gd doping, respectively. The resistivity shows little temperature dependence across a broad temperature range, indicating that in both types of films the transport is not dominated by phonon scattering. Gd-doped BaSnO3 films have a strong magnetic moment of ~7 µB/Gd ion. Such an optically transparent conductor with localized magnetic moments may unlock opportunities for multifunctional devices in the design of next-generation displays and photovoltaics. [ABSTRACT FROM AUTHOR]

Ferromagnetism at room temperature in (Ti,Co)O2 - δ was controlled by changing its electron density via chemical doping, where the oxygen vacancy δ served as an electron donor. With increasing the electron density, the ferromagnetic anomalous Hall effect and magnetization emerged from a paramagnetic state, while undergoing an insulator to metal transition. This result supports that the electron carriers mediated the ferromagnetic exchange interaction and is consistent with the electric field effect study on the ferromagnetism recently reported [Y. Yamada, K. Ueno, T. Fukumura, H. T. Yuan, H. Shimotani, Y. Iwasa, L. Gu, S. Tsukimoto, Y. Ikuhara, and M. Kawasaki, Science 332, 1065 (2011)]. [ABSTRACT FROM AUTHOR]

Single-phase PbPd0.81Co0.19O2 film with a body-centered orthorhombic structure was prepared using the sol-gel spin-coating technique and an oxidation treatment. Film resistivity has a power dependence on temperature. The insulator-metal transition temperature was 358 K, markedly higher than the reported values of similar material systems. Ferromagnetism and superparamagnetism coexisted in the film and the ferromagnetism persisted up to 380 K. As temperature increased, the notable increasing tendencies were found for the film's saturation magnetization and for the magnetic field where saturation magnetization decreases abruptly. The special spin gapless band structure and the film's nanograin microstructure are likely responsible for these interesting properties. [ABSTRACT FROM AUTHOR]

A sharp drop in resistance and a magnetization anomaly have been observed in La2/3Ca1/3MnO3 film in zero magnetic field at the BaTiO3 substrate structural phase transition temperature, due to the substrate clamping/strain effect, which is confirmed by Raman scattering. However, the anomalies for both resistance and magnetization were eliminated by a strong external magnetic field. These phenomena indicate that strain can cause colossal resistance and a change in magnetization which resembles the magnetic field effect. The interplay of the external forces (strain and magnetic field) is a good demonstration of the strong coupling between spin and lattice in colossal magnetoresistance materials. [ABSTRACT FROM AUTHOR]

The unusual behavior of negative remanent magnetization (NRM) that is observed in a simple homogeneous system consisting of two uniaxial anisotropies is explained quantitatively using an energy equation derived under the single domain assumption. The relative strength and alignment of the two uniaxial anisotropies and the direction of the applied magnetic field with respect to these anisotropies are identified as the three important factors for NRM. The window showing NRM is wider at larger angles between the two anisotropies and a maximum in NRM occurs near the boundary between NRM and ordinary positive remanent magnetization. [ABSTRACT FROM AUTHOR]

Using density matrix equations of motion and a tight-binding band calculation, we predict all-optical switching between four metastable magnetic states of (III,Mn)As ferromagnets. This switching is initiated non-thermally within 100 fs, during nonlinear coherent photoexcitation. For a single optical pulse, magnetization reversal is completed after ∼100 ps and controlled by the coherent femtosecond photoexcitation. Our predicted switching comes from magnetic nonlinearities triggered by a femtosecond magnetization tilt that is sensitive to un-adiabatic light-induced spin interactions. [ABSTRACT FROM AUTHOR]

Density functional theory with local spin density approximation is applied to study the evolution of ferromagnetism in SrxPb1-xRuO3 (0≤x≤1). Besides the enhanced Pb-O covalence and Pb-Ru hybridization, the Jahn-Teller effect, which favors the low-spin state (S=0) of Ru4+ in a stretched oxygen octahedra, is found to be the origin of the observed paramagnetism in PbRuO3. With the introduction of Sr, the Pb-Ru hybridization is weakened and an intermediate-spin state (S=1) is preferred via the opposite Jahn-Teller effect in a compressed oxygen octahedra, leading to the appearance of ferromagnetism for x>0.5. Our calculations provide a good explanation of recent experimental findings. [ABSTRACT FROM AUTHOR]

Near room temperature, MnAs films align into two phases, one ferromagnetic and the other paramagnetic. These phases take the intriguing form of nanoscale wires. We have exploited this phase coexistence to form linear arrays of magnetite nanoparticles without the need for photolithography. This is confirmed via extensive scanning probe microscopy. [ABSTRACT FROM AUTHOR]

Substitution of some Cr for Mn atoms in MnCoGe was employed to control the magnetic and structural transitions in this alloy to coincide, leading to a single first-order magnetostructural transition from the ferromagnetic to the paramagnetic state with a giant magnetocaloric effect observed near room temperature. Further increase in the Cr content in the Mn1-xCrxCoGe alloys can induce another first-order magnetoelastic transition from the antiferromagnetic to the ferromagnetic state occurring at lower temperature. The giant magnetocaloric effect as well as the simultaneous tunability of the two magnetic transitions make these materials promising for future cooling applications. [ABSTRACT FROM AUTHOR]

We report a systematic study of the film thickness dependence (0.1–1 μm) of room-temperature ferromagnetism in pure magnetron-sputtered ZnO thin films wherein a sequential transition from ferromagnetism to paramagnetism and diamagnetism as a function of film thickness is observed. The highest saturation magnetization (MS) value observed is 0.62 emu/g (0.018 μB/unit cell) for a ∼480 nm film. On doping the ZnO film with 1 at. % Mn enhances the MS value by 26%. The ferromagnetic order in ZnO matrix is believed to be defect induced. In addition, on doping with Mn hybridization between the 2p states of O and the 3d states of Mn occurs. [ABSTRACT FROM AUTHOR]

We report pulsed laser deposition synthesis and characterization of polycrystalline Fe1-xCoxSi thin films on Si (111). X-ray diffraction, transmission electron, and atomic force microscopies reveal films to be dense, very smooth, and single phase with a cubic B20 crystal structure. Ferromagnetism with significant magnetic hysteresis is found for all films including nominally pure FeSi films in contrast to the very weak paramagnetism of bulk FeSi. For Fe1-xCoxSi this signifies a change from helimagnetism in bulk, to ferromagnetism in thin films. These ferromagnetic thin films are promising as a magnetic-silicide/silicon system for polarized current production, manipulation, and detection. [ABSTRACT FROM AUTHOR]

We report on the electrical field control of ferromagnetism (FM) at room temperature in III-N dilute magnetic semiconductor (DMS) films. A GaMnN layer was grown on top of an n-GaN substrate and found to be almost always paramagnetic. However, when grown on a p-type GaN layer, a strong saturation magnetization (Ms) was observed. This FM in GaMnN can be controlled by depletion of the holes in the GaMnN/p-GaN/n-GaN multilayer structures. We have demonstrated the dependence of the FM on the thickness of the p-GaN in this heterostructure and on the applied bias to the GaN p-n junction. The Ms was measured by an alternating gradient magnetometer (AGM) and a strong correlation between the hole concentration near the GaMnN/p-GaN interface and the magnetic properties of the DMS was observed. At room temperature an anomalous Hall effect was measured for zero bias and an ordinary Hall effect for reverse bias in a fully depleted p-GaN layer. This is in close agreement with the AGM measurement results. [ABSTRACT FROM AUTHOR]

We proposed an explanation of the recent observations by Zaretsky [Appl. Phys. Lett. 92, 011913 (2008)] who discovered sharp increase in nickel plasticity under impact loading near Curie temperature TC. Growth of plasticity is explained by reduction in dynamical deceleration of dislocations controlled by their interaction with paramagnetic obstacles. The decreased contribution of these obstacles is due to spin-dependent transitions in internal magnetic field of ferromagnetic in radical pair dislocation-obstacle from strong to weak bonding states. The main contribution to the effect is from fields of magnetic fluctuations which have a large growth near Curie point. [ABSTRACT FROM AUTHOR]

Magnetic and transport properties of ferromagnetic semiconductors (FMSs) near the ferromagnetic-paramagnetic phase transition were studied in two classes of FMSs: in the III–V-based In1-xMnxSb and Ga1-xMnxAs epitaxial films and in IV–VI-based Sn1-xMnxTe and Sn1-x-yMnxEryTe alloys in bulk crystal form. Magnetoresistance data for both FMS classes are in excellent agreement with the theory of Majumdar and Littlewood, indicating that near the Curie temperature, magnetic fluctuations play a key role as scattering centers. These results also show that the Majumdar–Littlewood model can be applied to magnetically very dilute systems. [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]

The magnetic behavior of titanium dioxide nanobelts has been investigated with and without Co doping. Room temperature ferromagnetism was observed when the Co-doped anatase TiO2 nanobelts were prepared via vacuum annealing of 2.5 at. % Co-doped titanate nanobelts, while annealing them in air resulted in paramagnetic ordering. Interestingly, by vacuum annealing the undoped titanate nanobelts under the same conditions, superparamagnetic ordering was observed in the resulting anatase TiO2 nanobelts. The electron paramagnetic resonance of this latter sample shows a strong symmetrical signal at g=2.003 suggesting some sort of exchange interactions among the localized electrons’ spin moments from single electron trapped in oxygen vacancies. [ABSTRACT FROM AUTHOR]

The Laves phase compound YCo2 is a well-known exchange-enhanced Pauli paramagnet. We report here that, in the nanocrystalline form, this compound interestingly is an itinerant ferromagnet at room temperature with a low coercive field. The magnitude of the saturation moment (about 1μB per formula unit) is large enough to infer that the ferromagnetism is not a surface phenomenon in these nanocrystallites. Since these ferromagnetic nanocrystallites are easy to synthesize with a stable form in air, one can explore applications, particularly where the hysteresis is a disadvantage. [ABSTRACT FROM AUTHOR]

We present the structural and physical properties of epitaxial Bi2CoMnO6 films grown on SrTiO3 and LaAlO3. They display magnetic hysteresis loop with 170 Oe coercivity and a 3.1μB/f.u. saturation magnetization which indicates a disordered Co/Mn state. Nevertheless, these films display an unusually large ferromagnetic Curie temperature of about 800 K. We propose that the large Curie temperature is the result of a strong coupling between the magnetization and the polarization order parameters of Bi2CoMnO6 promoted by substantial structural changes in the films with respect to the bulk. These structural modifications amplify the overlap of the electronic wave functions of the Mn–O–Mn, Mn–O–Co and Co–O–Co bonds and the Bi 6s2 lone pair electrons providing the long-range spin order through the minimization of the magnetoelastic energy. [ABSTRACT FROM AUTHOR]

We report on the appearance of magnetic stripes in MnAs/GaAs(100) epilayers at temperatures well below the ferromagnetic transition of the system. The study has been performed by ferromagnetic resonance (FMR) experiments on MnAs epilayers grown on the (100) and (111) GaAs substrates. The FMR spectra of the MnAs/GaAs(100) samples at 180 K reveal the appearance of zones of different magnetic behaviors with respect to the low-temperature homogeneous ferromagnetic phase. The angular and the temperature dependences of the spectra serve us to detect the intergrowth of the nonmagnetic phase into the ferromagnetic phase at a very early stage of the process. The experimental data show that the paramagnetic phase nucleates in a self-arranged array of stripes in MnAs/GaAs(100) thin films while it grows randomly in the same films grown on GaAs(111). [ABSTRACT FROM AUTHOR]

Room-temperature ferromagnetism has been observed in Fe-doped PbTiO3 nanocrystals. The magnetism of the nanocrystals develops from diamagnetism to ferromagnetism and the paramagnetism on increasing nominal Fe doping concentration from 0 to 4 mol %. Transmission electron microscope (TEM) and high-resolution TEM data indicate that Fe-doped PbTiO3 nanocrystals with the size of ∼100 nm are organized to form a planarlike self-assembly via oriented aggregation. These assembled nanostructures effectively improve room-temperature ferromagnetism of the sample. The exchange interaction of ferric ions via an electron trapped in a bridging oxygen vacancy (F center) is employed to explain the ferromagnetism of Fe-doped PbTiO3 nanocrystals. [ABSTRACT FROM AUTHOR]

The structural and the magnetic properties of spin- and charge-doped Sr0.8La0.2Ti0.9Co0.1O3 have been investigated. The sample shows a cubic structure at room temperature. The temperature dependence of magnetization (M) of Sr0.8La0.2Ti0.9Co0.1O3, in both zero-field-cooled (ZFC) and field-cooled (FC) modes between 100 and 70 000 Oe, was measured. It is found that the sample undergoes the paramagnetic-ferrimagnetic phase transition at around 50 K, and the MZFC curve lies above the MFC one below 32 K when the applied field is less than 2000 Oe. This unusual behavior can be understood as a superposition of ferrimagnetic and paramagnetic contributions to the magnetization. [ABSTRACT FROM AUTHOR]

The Curie temperature of diluted magnetic semiconductor (DMS) nanowires and nanoslabs is investigated using the mean-field model. The Curie temperature in DMS nanowires can be much larger than that in corresponding bulk material due to the density of states of one-dimensional quantum wires, and when only one conduction subband is filled, the Curie temperature is inversely proportional to the carrier density. The TC in DMS nanoslabs is dependent on the carrier density through the number of the occupied subbands. A transverse electric field can change the DMS nanowires from the paramagnet to ferromagnet, or vice versae. [ABSTRACT FROM AUTHOR]

Polycrystalline Zn0.95Co0.05O is found to be paramagnetic at room temperature and down to 12 K. Optical measurements prove the incorporation of Co2+ ions inside the ZnO lattice in the tetrahedral site. When the paramagnetic sample is heated in Ar/H2 at 1125 K for 2 h, ferromagnetism with a very high value of magnetization is observed at room temperature. Hydrogen reduction does not affect the substituted Co2+ ions inside the wurtzite crystal lattice as evidenced from optical studies. X-ray diffraction studies show the presence of Co metal after the reduction process which is the origin of room temperature ferromagnetism. [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]

Based on the projector augmented-wave method, ab initio calculations confirm the ground state is of ferromagnetic bcc Fe and reveal a paramagnetic state for the hcp Fe. Interestingly, the calculations predict that there exist at least three distinct magnetic orderings for the metastable fcc structured Fe—a paramagnetic and low-spin and high-spin ferromagnetic states—within a lattice constant ranging from 0.34 to 0.38 nm, and that, upon increasing the atomic volume of Fe, the magnetic moment is enhanced and can even be greater than that of the equilibrium bcc Fe. © 2004 American Institute of Physics. [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]

In this letter, we report the interface-related room temperature ferromagnetism in bulk CuO/Cu2O composites which were synthesized by heat-decomposing or oxidation methods with the CuO and Cu2O as the precursors, respectively. Magnetic measurement results indicate that all the CuO/Cu2O composites show obvious room temperature ferromagnetism, while the samples with the pure CuO and Cu2O phases are paramagnetic. What is more, the ferromagnetism can be tuned by changing the phase rations of the CuO and Cu2O in the composites. The observed ferromagnetism in CuO/Cu2O composites is considered to be related to the interface between CuO and Cu2O phases. [ABSTRACT FROM AUTHOR]