Search

Two-dimensional (2D) transition metal dichalcogenide (TMD) has emerged as an effective optoelectronics material due to its novel optical properties. Understanding the role of defects in exciton kinetics is crucial for achieving high-efficiency TMD devices. Here, we observe defects induced anomalous power dependence exciton dynamics and spatial distribution in hexagonal heterogeneous WS2. With transient absorption microscopy study, we illustrate that these phenomena originate from the competition between radiative and defect-related non-radiative decays. To understand the physics behind this, a decay model is introduced with two defect-related channels, which demonstrates that more excitons decay through non-radiative channels in the dark region than the bright region. Our work reveals the mechanisms of anomalous exciton kinetics by defects and is instrumental for understanding and exploiting excitonic states in emerging 2D semiconductors.

Based on the exact muffin-tin orbitals (EMTOs), we developed a first-principles method to calculate the current operators and investigated the anomalous Hall effect in bcc Fe as an example, with which we successfully separated the skew scattering contribution from the side jump and intrinsic contributions by fitting the scaling law with the introduction of sparse impurities. By investigating the temperature dependence of the anomalous Hall effect in bulk Fe, we predicted a fluctuated anomalous Hall angle as a function of temperature when considering only phonons, which, in the future, can be measured in experiments by suppressing magnon excitation, e.g., by applying a high external magnetic field.

Electrical contacts are crucial to the high performances of electronic devices, and they become more prominent for the popular two-dimensional (2D) semiconductors because they commonly have high contact resistances and are sensitive to the interfacial states. In this paper, taking monolayer MoS2 as an example, first-principles calculations are done to study and predict the influences of the contact mode on the interfacial electronic states of monolayer MoS2/metal (metal = Mg, Al, In, Cu, Ag, Au, Pd, Sc, and Ti). It is found that the interfacial properties are determined by the matching degree between the electronic states of the monolayer MoS2 and metal electrodes. The top contact configuration is preferred for the monolayer MoS2/Sc system as a result of an extremely low Schottky barrier (0.086 eV) as compared to that (0.439 eV) in the edge contact configuration, however, the edge contact configuration is preferred for Ag, Cu, Au, and Pd electrodes. Furthermore, metal electrodes in the top contact configuration might usually result in n-type doping of monolayer MoS2, but lead to p-type doping in the edge contact configuration. The pinning factor S (0.257, −0.009, −0.132, and −0.172) of monolayer MoS2 in both contact modes is close to zero, suggesting a strong electronic pinning effect. The findings provide theoretical guidance for the selection of electrodes for high-performance 2D material based devices.

The stability of lattice dynamics and the magnetism of the ordered γ′-Fe4N crystalline alloy at high pressures were studied by first-principle calculations based on density-functional theory. The dynamical stable new phase P2/m-Fe4N at high pressures was found by conducting the softening phenomenon at the point M (0.5 0.5 0) of the acoustic phonon at 10 GPa in the γ′-Fe4N via soft-mode phase transition theory. Compared to the phonon spectrum of γ′-Fe4N without considering electronic spin polarization, the ground-state lattice dynamical stability of the ferromagnetic phase γ′-Fe4N is induced by the spontaneous magnetization at pressures below 1 GPa. However, P2/m-Fe4N is more thermodynamically stable than γ′-phase at pressures below 1 GPa, and the magnetic moments of the two phases are almost the same. The ground-state structure of P2/m phase is more stable than that of γ′-phase in the pressure range from 2.9 to 19 GPa. The magnetic moments of the two phases are almost the same in the pressure range from 20 to 214 GPa, but the ground-state structure of γ′-phase is more stable than that of P2/m phase in the pressure range from 143.8 to 214 GPa. On the contrary, the ground-state structure of P2/m phase is more stable when the pressure is above 214 GPa. In the pressure range from 214 to 300 GPa, the magnetic moment of P2/m phase is lower than that of γ′-phase, and the magnetic moments of the two phase tend to be consistent when the pressure exceeds 300 GPa.

The magnetic states of one single atomic layer of iron epitaxially grown on 4d and 5d nonmagnetic metals are studied under strain systematically using first principle calculations. Our results show that, without strain, the iron on top of different 4d and 5d nonmagnetic metals shows distinct antiferromagnetic or ferromagnetic ground states: a parallel antiferromagnetic ground state (p-AFM) on Rh and a central antiferromagnetic ground state (c-AFM) on Ir and ferromagnetic (FM) ground state on Pd, Ag, Pt and Au. However, when introducing in-plane biaxial and uniaxial strain (Δexx) on the substrates, the ground state of iron can be manipulated easily. In detail, for biaxial strain, the ground state of iron on an Rh substrate becomes FM when Δexx 0.8%, and on an Ir substrate, the ground state of iron becomes FM when Δexx –0.8%. However, for the uniaxial strain along the x direction, while using the corresponding Poisson's ratios to determine the strain along the y direction, the ground state of iron on an Rh substrate remains the p-AFM state, but on an Ir substrate, the ground state of iron changes from c-AFM to p-AFM at Δexx = 0.2% or Δexx = −0.3% along the x direction respectively.

Motivated by the rich physics of electric-field control of magnetic properties observed in recent experiments, we use the first-principles calculations to investigate charge-transfer-induced magnetism of the full $d$-band nonmagnetic metals. A ferromagnetic phase transition initiated by an electric-field-induced charge transfer was found for all full $d$-band nonmagnetic metals. Beside the ordinary Hund's rules in Cu and Ag, a more complex correlation between the charge and the induced magnetization has been found, especially in Pd. The origin of the abnormal charge-induced magnetization is determined by the Coulomb interaction-induced instability of spin degeneracy at specific charges. In addition, a large nontrivial anomalous Hall effect has been discovered, and the sign of the anomalous Hall conductivity can change as charge number varies, a feature potentially useful for future spintronic applications.

Understanding the physical mechanism of wetting transitions is crucial for the design of highly stable superhydrophobic materials. Wetting transitions from Cassie state to Wenzel state on microstructured surfaces were investigated in this article. The pinning force τ was introduced to establish a new mechanical equilibrium, obtaining the model of critical pressure p c of Cassie-Wenzel wetting transition and the model was qualitatively verified by performing a series of experiments. Using the model of p c and experimental data, the pinning force τ on different microstructured surfaces was obtained.

We investigated the temperature dependence of thermally excited spin current properties of ferromagnet Py $({\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20})$ by using a lateral spin-valve structure. The spin-dependent Seebeck coefficient at the Py/Cu interface was found to show a significant increase at low temperature while the charge Seebeck coefficient showed the ordinal reduction with decreasing temperature. This produces a crossover between the charge- and spin-dependent Seebeck coefficients, resulting in the thermal spin polarization greater than $100%$ below 125 K. From the first-principles calculation specially developed for the Py/Cu interfaces, the spin-dependent Seebeck coefficient is found to be highly susceptible to the magnetic disorder-induced scattering at the interface. The calculation with considering the temperature dependence of the magnetic disorder provides a consistent description for the significant enhancement of spin-dependent Seebeck coefficient in the Py/Cu interface. Our demonstration shows the importance of interface disorder and paves the way toward the development of conventional ferromagnetic metal for the practical application of thermo-spin energy conversion.

E-field control of antiferromagnetic (AFM) orders is promising for the realization of fast, compact, and energy-efficient AFM applications. However, as the AFM spins are strongly pinned, the E-field control process is mainly based on the exchange bias regulation that usually confines at a low temperature. Here, a new magnetoelectric (ME) coupling mechanism for the modulation of AFM orders at room temperature is explored. Based on the FeCoB/Ru/FeCoB/(011) Pb(Mg1/3 Nb2/3 )O3 -PbTiO3 (PMN-PT) synthetic antiferromagnetic (SAF) heterostructures, the external E-field generates relative magnetization switching in the two ferromagnetic (FM) layers, leading the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction tuning. This voltage-induced switching behavior can be repeated in a stable and reversible manner for various SAFs, which is a key challenge in the E-field control of AFM coupling and is not resolved yet. The voltage-induced RKKY interaction changes by analyzing the dynamic optical and acoustic modes is quantified, and with first-principles calculations, it is found that the distortion of the Fermi surface by the lattice reconstruction is the key of the relative magnetization switching and RKKY interaction modulation. This voltage control of the RKKY interaction in ME heterostructures provides an easy way to achieve the next generation of AFM/FM spintronic applications.

To overcome the fundamental challenge of the weak natural response of antiferromagnetic materials under a magnetic field, voltage manipulation of antiferromagnetic interaction is developed to realize ultrafast, high-density, and power efficient antiferromagnetic spintronics. Here, we report a low voltage modulation of Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction via ionic liquid gating in synthetic antiferromagnetic multilayers of FeCoB/Ru/FeCoB and (Pt/Co)2/Ru/(Co/Pt)2. At room temperature, the distinct voltage control of transition between antiferromagnetic and ferromagnetic ordering is realized and up to 80% of perpendicular magnetic moments manage to switch with a small-applied voltage bias of 2.5 V. We related this ionic liquid gating-induced RKKY interaction modification to the disturbance of itinerant electrons inside synthetic antiferromagnetic heterostructure and the corresponding change of its Fermi level. Voltage tuning of RKKY interaction may enable the next generation of switchable spintronics between antiferromagnetic and ferromagnetic modes with both fundamental and practical perspectives. Energy efficient control of magnetization in antiferromagnetic materials is one of the key ingredients for antiferromagnetic spintronics. Here the authors demonstrate voltage control of RKKY interaction and magnetization switching in synthetic antiferromagnetic multilayers by ionic liquid gating.

The effect of four different seed layers-Ru, Hf/Ru, Ru/Hf, and Hf on the magnetic properties of [Co 5/Pt 3 A] multilayer (ML) stack with perpendicular magnetic anisotropy was investigated. The structural quality of the ML stacks was studied and correlated with the magnetic properties. Among the abovementioned seed layers, Ru promotes stronger fcc (111) texture in the ML due to less lattice mismatch (8% between Ru and Co) in Co/Pt MLs. As a result, higher anisotropy field (H K ~ 17 kOe) and larger effective perpendicular anisotropy (K eff ~ 1.2 × 10 7 erg/cm 3 ) were achieved for the MLs on Ru seed layer compared with other seed layers after annealing at 300 °C for 30 min. The perpendicular magnetic anisotropy of the MLs is improved at higher annealing temperature up to 400 °C for Ru and Hf/Ru seed layer. For the Co/Pt MLs on Ru, 1.3 × 10 7 erg/cm 3 perpendicular magnetic anisotropy was obtained even after annealing at 400 °C. Detail investigations of postannealing stability of the ML films on different seed layers were also discussed. The magnetic properties and structural properties of the films on four different seed layers were characterized after rapid thermal annealing process at 300 °C, 350 °C, and 400 °C for 30 min annealing duration. The high temperature endurance limit up to 400 °C for 30 min of the Co/Pt MLs on Ru and Hf/Ru seed layers makes them compatible with the back-end-of-line process temperature.

We analyze the opportunity of inserting a Ta layer between the polarizing section and the high anisotropy section in the reference subsystem of CoFeB-based tunnel junctions with perpendicular magnetic anisotropy. Using vector network analyzer ferromagnetic resonance, polar Kerr magnetometry, and magnetization dynamics modeling, we deduce the strength of the ferromagnetic interlayer exchange coupling energy J through various thickness of tantalum that impacts on the overall performance of the tunnel junctions. J culminates at 0.44 mJ/m 2 through 3 A of Ta, but the Co/Pt properties are then suboptimal. Our methodology can be used to rationally find the performance optimum in the reference layers of perpendicularly magnetized tunnel junctions.

The elementary excitation spectra of a one-dimensional ferrimagnetic diamond chain in the spin-1/2 XY model at low temperatures have been calculated by using an invariant eigen-operator (IEO) method, the energies of elementary excitations in different specific cases are discussed, and the analytic solutions of three critical magnetic field intensities (HC1, HC2, and Hpeak) are given. The magnetization versus external magnetic field curve displays a 1/3 magnetization plateau at low temperatures, in which HC1 is the critical magnetic field intensity from the disappearance of the 1/3 magnetization plateau to spin-flop states, HC2 is the critical magnetic field intensity from spin-flop states to the saturation magnetization, and Hpeak is the critical magnetic field intensity when the temperature magnetization shows a peak in the external magnetic field. The temperature dependences of the magnetic susceptibility and the specific heat show a double peak structure. The entropy and the magnetic susceptibility versus external magnetic field curves also exhibit a double peak structure, and the positions of the two peaks correspond to HC1 and HC2, respectively. This derives from the competition among different types of energies: the temperature-dependent thermal disorder energy, the potential energy of the spin magnetic moment, the ferromagnetic exchange interaction energy, and the anti-ferromagnetic exchange interaction energy. However at low temperatures, the specific heat as a function of external magnetic field curve exhibits minima at the above two critical points (HC1 and HC2). The origins of the above phenomena are discussed in detail.

In order to improve the properties of nano graded ferroelectric films (NGFF), the generalized Ginzburg-Landau-Denvonshire (GLD) theory is used to investigate the ferroelectric and pyroelectric properties of NGFF. A function is introduced to describe the local structure of this graded film. The numerical results show that parameter and film thickness are two very important factors that influence the ferroelectric and pyroelectric properties of films, larger values lead to smaller spontaneous polarization and lower pyroelectric peak Local structure in NGFF leads to flatten the polarization distribution, which raises the spontaneous polarization of components with lower transition temperature, but reduces spontaneous polarization of components with higher transition temperature.

In order to improve the pyroelectric properties of nanograded ferroelectric films (NGFF), and provide a theoretical reference for practical applications, the generalized Ginzburg-Landau-Denvonshire (GLD) theory is adopted to investigate the pyroelectric properties of the NGFF. A function is introduced to characterize the local structure in nanograded films. Influence of the local structure, film thickness and external electric field on the polarization distribution and pyroelectric properties are mainly discussed. The numerical results show that parameterand film thickness are two very important factors that influence the film properties, larger values lead to smaller spontaneous polarization and lower pyroelectric peak. Different directions of the external electric field can lead to greatly different effects on pyroelectric behaviors, whose effects is to expand the working temperature region, or else, change the order of phase transition.

Ce-doped LaMnO 3 has complicated physical properties, such as unclear valence states of Ce and Mn ions, ferromagnetism― paramagnetism and metal-insulator transitions, and multiphase coexistence. To explore the ground-state properties of single-phase La 1―x Ce x MnO 3 and obtain better understanding of the complicated physical properties of the multiphase system, the electronic and magnetic structures of La 1―x Ce x MnO 3 are investigated by using the first principle calculations. The results show that single phase La 1 ―x Ce x MnO 3 is neither a hole-doped nor an electron-doped compound. The valence states of Ce and Mn ions are predicted to be trivalent in an ionic picture. Trivalent Mn ions energetically favor an A-type antiferromagnetic ordering and insulating band structure. In comparison with the experimental studies, it is concluded that overoxygenation and multiphase coexistence in experiments switch the ground state from an antiferromagnetic insulator to a ferromagnetic half-metal.

Electric field (E-field) modulation of perpendicular magnetic anisotropy (PMA) switching, in an energy-efficient manner, is of great potential to realize magnetoelectric (ME) memories and other ME devices. Voltage control of the spin-reorientation transition (SRT) that allows the magnetic moment rotating between the out-of-plane and the in-plane direction is thereby crucial. In this work, a remarkable magnetic anisotropy field change up to 1572 Oe is achieved under a small operation voltage of 4 V through ionic liquid (IL) gating control of SRT in Au/[DEME]+ [TFSI]- /Pt/(Co/Pt)2 /Ta capacitor heterostructures at room temperature, corresponding to a large ME coefficient of 378 Oe V-1 . As revealed by both ferromagnetic resonance measurements and magnetic domain evolution observation, the magnetization can be switched stably and reversibly between the out-of-plane and in-plane directions via IL gating. The key mechanism, revealed by the first-principles calculation, is that the IL gating process influences the interfacial spin-orbital coupling as well as net Rashba magnetic field between the Co and Pt layers, resulting in the modulation of the SRT and in-plane/out-of-plane magnetization switching. This work demonstrates a unique IL-gated PMA with large ME tunability and paves a way toward IL gating spintronic/electronic devices such as voltage tunable PMA memories.

Generalized gradient approximation (GGA) and GGA + U (U denotes on-site Coulomb interactions) methods are applied to investigate the magnetic and electronic structures of the perovskite oxide Nd2/3Sr1/3MnO3. Under GGA the compound prefers ferrimagnetic ordering in which Nd sublattice is spin-antiparallel to Mn sublattice. Nd 4f states cross over the Fermi level under GGA, leading the ferrimagnetic Nd2/3Sr1/3MnO3 to a metallic character. The on-site Coulomb interactions should be included to emphasize the localized feature of Nd 4f states. Under GGA + U, the spins of Nd and Mn sublattices tend to be parallel in the ground state, and fully spin-polarized Mn 3d electrons yield a half-metallic band structure for the ferromagnetic Nd2/3Sr1/3MnO3. The ferromagnetic coupling between Nd and Mn sublattices is ascribed to the super-exchange interaction between Nd 4f and Mn 3d ( t 2 g ) electrons via O 2p electrons.

Key design parameters of 64 Mb STT-MRAM at 90-nm technology node are discussed. A design point was developed with adequate TMR for fast read operation, enough energy barrier for data retention and against read disturbs, a write voltage satisfying the long term reliability against dielectric breakdown and a write bit error rate below 10-9. A direct experimental method was developed to determine the data retention lifetime that avoids the discrepancy in the energy barrier values obtained with spin current- and field-driven switching measurements. Other parameters detrimental to write margins such as backhopping and the existence of a low breakdown population are discussed. At low bit-error regime, new phenomenon emerges, suggestive of a bifurcation of switching modes. The dependence of the bifurcated switching threshold on write pulse width, operating temperature, junction dimensions and external field were studied. These show bifurcated switching to be strongly influenced by thermal fluctuation related to the spatially inhomogeneous free layer magnetization. An external field along easy axis direction assisting switching was shown to be effective for significantly reducing the percentage of MTJs showing bifurcated switching.

A magnon–phonon interaction model is set up in a two-dimensional ferromagnetic compound square-lattice system. By using Matsubara Green function theory we have calculated the magnon damping on the main symmetric lines in the Brillouin zone, compared the influences of magnetic ion optical-mode phonon and non-magnetic ion optical-mode phonon on the magnon damping of the system, and discussed the influences of the parameter variations and temperature on the magnon damping. The results show that the coupling of the optical-mode phonon and the magnon plays an important role for the magnon damping, especially the longitudinal optical-mode phonon contributes the most for the magnon damping. It is also found that the effect of the non-magnetic ion’s optical-mode phonon on magnon damping is more significant than that of the magnetic ion. By the expression − Im Σ ∗ ( 1 ) ( k ) = ħ / ( 2 τ ) , the magnon life-time and the magnon line-width are discussed either.

The effects of Nd-doping on the transport and magnetic properties of La 2/3− y Nd y Sr 1/3 MnO 3 ( y =0, 1/3, 2/3) are studied theoretically by using the generalized-gradient-corrected full-potential method. In order to investigate the coupling between Nd and Mn, the electronic structures of La 2/3− y Nd y Sr 1/3 MnO 3 with ferromagnetic (FM) and antiferromagnetic (AFM) arrangements of Nd and Mn sublattices are calculated. The calculation for FM La 2/3− y Nd y Sr 1/3 MnO 3 yields a half-metallic band structure, while the ferrimagnetic (FiM) system is found to have a metallic character. Hybridization of Nd 4f, Mn 3d, and O 2p bands around Fermi level ( E F ) is observed, suggesting the coupling between Nd and Mn is mediated by O 2p carriers. The qualitative features of transport and magnetic properties of such a two-spin system can be interpreted in terms of half-metallic FM domains being mixed up with metallic FiM domains. The proportion of FM domains varying with Nd-doping concentration has strong influences on the magnetoresistance.

A magnon–longitudinal acoustic (LA) phonon interaction model is developed on the basis of a two-dimensional square Heisenberg ferromagnetic system. The LA phonon excitation is studied by Matsubara–Green function theory, and the LA phonon excitation dispersion curves are calculated on the main symmetric lines in Brillouin zone (BZ). It is found that there exists obvious LA phonon hardening. The hardening of LA phonons becomes more evident near the M point of the BZ boundary. The influences of various parameters on LA phonon hardening are also discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A magnon–phonon interaction model is set up for a two-dimensional insulating ferromagnetic system. By using Matsubara function theory, we have studied the magnon spectrum and calculated the magnon dispersion curve on the main symmetric point and line in the Brillouin zone for various parameters of the system. The results show that at the boundary of Brillouin zone, there is a strong magnon softening. The contributions of longitudinal and transverse phonons on the magnon softening are compared and the influences of various parameters are also discussed.

A magnon–phonon interaction model is developed on the basis of two-dimensional square Heisenberg ferromagnetic system. By using Matsubara Green function theory transverse acoustic phonon excitation is studied and transverse acoustic phonon excitation dispersion curves is calculated on the main symmetric point and line in the first Brillouin zone. On line Σ it is found that there is hardening for transverse acoustic phonon on small wave vector zone (nearby point Γ ), there is softening for transverse acoustic phonon on the softening zone and there is hardening for transverse acoustic phonon near point M . On line Δ it is found there is no softening and hardening for transverse acoustic phonon. On line Z it is found that there is softening for transverse acoustic phonon on small wave vector zone (nearby point X ) and there is hardening for transverse acoustic phonon nearby point M . The influences of various parameters on transverse acoustic phonon excitation are also explored and it is found that the coupling of the magnon–phonon and the spin wave stiffness constant play an important role for the softening of transverse acoustic phonon.

A magnon–phonon interaction model is developed on the basis of a two-dimensional square Heisenberg ferromagnetic system. By using Matsubara Green function theory we studied the transverse and longitudinal acoustic phonon dampings and calculated the transverse and longitudinal acoustic phonon damping curves on the main symmetric point and line in the first Brillouin zone. It is found that on the line Δ there is no damping for transverse acoustic phonon and on the line Z there is no damping for longitudinal acoustic phonon. In the first Brillouin zone the damping of transverse acoustic phonons is at least one order larger than that of longitudinal acoustic phonons. The influences of various parameters on transverse and longitudinal acoustic phonon dampings are discussed and the lifetime and the density of state of transverse and longitudinal acoustic phonons are explored as well according to the relation of the phonon damping and its lifetime and the relation of the phonon damping and its density of state.

A magnon–phonon interaction model is set up for a two-dimensional insulating ferromagnetic system. By using Matsubara function theory we have studied the magnon damping − I m Σ ∗ ( 1 ) ( k → ) and calculated the magnon damping − I m Σ ∗ ( 1 ) ( k → ) curve on the main symmetric point and line in the Brillouin zone for various parameters in the system. It is concluded that at the boundary of Brillouin zone there is a strong magnon damping. However, the magnon damping is very weak on the zone of small wave vector and the magnon damping reaches maximal value at very low temperature. The contributions of longitudinal phonon and transverse phonon on the magnon damping are compared and the influences of various parameters are also discussed.

Excellent tunnel magneto resistance (TMR) values of 143% at resistance-area products (RA) of 4.7 Ωµm2 from 11nm thin Co/Ni based perpendicular magnetic tunnel junctions (p-MTJ) was achieved. Engineered wetting layer (WL), seed layer (SL) and the introduction of newly designed inner synthetic anti-ferromagnetic (iSAF) pinned layer in combination with ultra-smooth bottom electrode (roughness 0.5 A) was yielded to vertically scaled 11nm thick Co/Ni p-MTJ stack with excellent magnetic properties. The introduction of iSAF layer demonstrates for the 1st time the free layer offset field controllability (< 100 Oe) of the spin-transfer-torque (STT) magnetic random access memory (MRAM) device down to 12 nm in diameter.

Using experimental and micromagnetic modeling, the intermediate magnetization states in deep submicrometer MRAM cells, their effects on the switching behavior and designs to eliminate them, are presented. The elliptical MRAM cell with varied aspect ratio and minor axis length is built using synthetic pinned layer-AlO/sub x/-free layer structure. At-field and remnant R-H curves are collected for various design and process parameters: free layer thickness, cell aspect ratio, different free layer material NiFe, CoFe, CoFeB and combinations of them. For not well optimized designs, the at-field R-H curves are not desirable squares with significant amount of irregularities or kinks that can be separated into two types: type V and type H. From micro-magnetic modeling, the magnetization of the type V kink state is identified as vortex configuration. For the type H, the magnetization state has a horseshoe configuration.

We report detailed transport measurements in a quantum dot in a spin-flip co-tunneling regime, and a quantitative comparison of the data to microscopic theory. The quantum dot is fabricated by lateral gating of a GaAs/AlGaAs heterostructure, and the conductance is measured in the presence of an in-plane Zeeman field. We focus on the ratio of the nonlinear conductance values at bias voltages exceeding the Zeeman threshold, a regime that permits a spin flip on the dot, to those below the Zeeman threshold, when the spin flip on the dot is energetically forbidden. The data obtained in three different odd-occupation dot states show good quantitative agreement with the theory with no adjustable parameters. We also compare the theoretical results to the predictions of a phenomenological form used previously for the analysis of non-linear co-tunneling conductance, specifically the determination of the heterostructure g-factor, and find good agreement between the two., Comment: 5 pages, 5 figures

We have measured the magnetic splitting, $\Delta_K$, of a Kondo peak in the differential conductance of a Single-Electron Transistor while tuning the Kondo temperature, $T_K$, along two different paths in the parameter space: varying the dot-lead coupling at a constant dot energy, and vice versa. At a high magnetic field, $B$, the changes of $\Delta_K$ with $T_K$ along the two paths have opposite signs, indicating that $\Delta_K$ is not a universal function of $T_K$. At low $B$, we observe a decrease in $\Delta_K$ with $T_K$ along both paths, in agreement with theoretical predictions. Furthermore, we find $\Delta_K/\Delta1$ at high $B$, where $\Delta$ is the Zeeman energy of the bare spin, in the same system., Comment: 12 pages, 5 figures

We report a zero-bias peak in the differential conductance of a Quantum Point Contact (QPC), which splits in an external magnetic field. The peak is observed over a range of device conductance values starting significantly below $2e^2/h$. The observed splitting closely matches the Zeeman energy and shows very little dependence on gate voltage, suggesting that the mechanism responsible for the formation of the peak involves electron spin. Precision Zeeman energy data for the experiment are obtained from a separately patterned single-electron transistor located a short distance away from the QPC. The QPC device has four gates arranged in a way that permits tuning of the longitudinal potential, and is fabricated in a GaAs/AlGaAs heterostructure containing 2-dimenional electron gas. We show that the agreement between the peak splitting and the Zeeman energy is robust with respect to moderate distortions of the QPC potential. We also show that the mechanism that leads to the formation of the ZBP is different from the conventional Kondo effect found in quantum dots., Comment: 10 pages, 6 figures

This article presents a micromagnetic study on the dynamics of magnetic flux transfer in the pole tip region of a stitched-pole magnetoresistance/thin-film head. Three-dimensional vortices are found inside the pole tips. The flux at the ABS surface is conducted by the motion of the vortex moving in the cross-track direction. The resulting head field well follows the driving flux with little phase delay and little dependence on the damping constant, α. The vortex motion under the driving flux maintains similar speed even when the damping constant is decreased to zero. In this case, it is found that in addition to the motion of the vortex, spins precess locally with small cone angles, resulting in small head field fluctuations. It is concluded that the speed of magnetization flux reversal in the pole tip region is not limited by small damping constant.

By using projection augmented plane wave method (PAW) and based on the density functional theory, the stability of lattice dynamics and the magnetism of ordered crystalline alloy -Fe4N are studied at high external pressures. In comparison with the phonon spectrum of -Fe4N without considering the spin-polarization, it is found that the ground-state lattice dynamics stability of the ferromagnetic phase -Fe4N is induced by the spontaneous magnetization at pressures below 1 GPa. The phonon spectra at point (0.37, 0.37, 0) in line , points X and M become softening at pressures between 1.03 and 31.5 GPa. The pressure-induced effect and the spontaneous magnetization effect on the atoms reach a stable equilibrium state at the pressures between 31.5 and 60.8 GPa, which result in the phonon spectrum stability. As the pressure exceeds 61.3 GPa, the system becomes more instable dynamically with the increase of the external pressure. The softening at point M of the acoustic phonon is treated by the soft-mode phase theory at 10 GPa, and a new dynamic stability high-pressure phase with a space group of P2/m is found. This new phase is thermodynamically stable and possesses the same magnetic moments as that of -Fe4N at pressures below 1 GPa. The enthalpy value of the phase P2/m is less than that of phase at the pressures between 2.9 and 19 GPa, therefore its ground-state structure is more stable. As the pressure exceeds 20 GPa, both phases possess almost the same magnetic moments.

The ordered crystalline Fe3Pt invar alloy is in a special magnetic critical state under which the lattice dynamic stability of the system is extremely sensitive to the external pressure. Using projection augmented plane wave method based on the density functional theory, we calculate the dependences of enthalpy and magnetism of different crystalline alloys of Fe3Pt on external pressure. The results reveal that the P4/mbm structure is thermodynamically stable under pressures below 18.54 GPa. The total magnetic moments of Pm3m, I4/mmm and DO22 structures decrease rapidly and oscillate near the ferromagnetic collapse critical pressure. Furthermore in I4/mmm and DO22 structures the atomic magnetic moment of Fe1 reverses near the critical pressure. At a pressure of 43 GPa, the micro-ferrimagnetic property in DO22 structure becomes apparently strengthened while its volume increases rapidly. The lattice dynamic calculation shows that the spontaneous magnetization of the system in ferromagnetic states induces the softening of the transverse acoustic phonon TA1(M) in the Fe3Pt of Pm3m structure, and there exists a strong spontaneous volume magnetostriction at pressures below 26.95 GPa. Especially, in the pressure range between the ferromagnetic collapse critical pressure 41.9 GPa and the magnetism completely disappearing pressure 57.25 GPa, the lattice dynamic stability is more sensitive to the pressure. The pressure induces the stability of the phonon spectrum of the system at pressures above 57.25 GPa.

The effect of grain size dispersion on medium noise in longitudinal thin film recording media is studied by micromagnetic modeling. A previous micromagnetic model has been extended for modeling films with grain size variation. It is found that for the typical thin film media, moderate grain size dispersion in the film does not affect the media noise at low recording densities. At high recording densities, when adjacent transition boundaries percolate, the film with grain size dispersion exhibits a less degree of superlinear noise enhancement than the film with identical size grains. It is concluded that for films with medium noise dominated by magnetic interactions, moderate grain size dispersion slightly suppresses the collective magnetization processes at high recording densities, thereby, reducing medium noise.

Wetting transitions were studied with vertically vibrated droplet on various polydimethylsiloxane surfaces with square array of pillars. Our experiments show that the increase of the pillar spacing, at each given frequency, leads to a decrease of the critical amplitude (which is required to achieve a Wenzel to Cassie transition). The physical mechanism of Wenzel-Cassie transition by vibration is presented. Compared with other studies of wetting transition by vibration, we demonstrate that Wenzel-Cassie transition comes up when R(θ)fn2Acr2≈const (where fn is the resonance frequency, Acr is the threshold amplitude, and R(θ) is the initial radius of the droplet).