Search

Rare-earth free, ferromagnetic MnBi shows a positive temperature coefficient of coercivity from room temperature to 400 K and energy product (BH)max of 17.7 MGOe at 300 K. However, MnBi undergoes a first-order structural phase transformation from a ferromagnetic low-temperature phase (LTP) to a paramagnetic high-temperature phase at 613 K below the Curie temperature (Tc) of 716 K. The transformation is attributed to Mn diffusion into the interstitial site of LTP MnBi unit cell. Interstitial Mn antiferromagnetically couples with the Mn at lattice 2a site, lowering the magnetization. Cu-occupied bipyramidal sites are investigated as a possible means to suppress Mn diffusion into the bipyramidal sites using first-principles calculations based on the density functional theory. Saturation magnetization, magnetocrystalline anisotropy constant (K), and Tc of (Mn0.5Bi0.5)100−xCux (x = 0–33) are reported. The magnetocrystalline anisotropy changes to the out-of-plane direction (x = 13) from the in-plane direction (x = 0.0). Tc decreases gradually to 578 K at x = 33 from 716 K at x = 0.0. The calculations show a slightly lower (BH)max of 15.6 MGOe while it is expected that Cu-occupied interstitial sites will significantly suppress Mn diffusion and raise the temperature of the phase transformation. [ABSTRACT FROM AUTHOR]

Antiferromagnetic topological insulators have attracted great attention in the condensed matter physics owing to the fundamental interest in exotic quantum states and topological antiferromagnetic spintronics. Starting with the typical topological insulator of Bi2Te3, we introduced the magnetic order by substituting Gd at the Bi site and tuned the Fermi level by substituting Se at the Te site. That is, we prepared single crystals of GdxBi2−xTe3−ySey with various x (= 0.02 and 0.06) and y (= 0.1, 0.2, 0.5, 0.7, 1.0, and 1.5). The magnetic data revealed an antiferromagnetic order for x = 0.06, and the transport data manifested the charge neutral point at y = 0.7. Combining all these results together, the material with x = 0.06 and y = 0.7 is characterized as an antiferromagnetic topological insulator, where we observed exotic magnetotransport properties such as weak antilocalization and negative longitudinal magnetoresistance that are frequently analyzed as chiral anomalies in Weyl materials. [ABSTRACT FROM AUTHOR]

We investigated the thermal transport properties of magnetic van der Waals materials, TMPS3 (TM = Mn, Ni, and Fe), using the time-domain thermoreflectance technique. We determined the cross-plane thermal conductivity, which turns out to be relatively low, i.e., about 1 W m−1 K−1 for all TMPS3 investigated. When compared with previous results of graphite and transition metal dichalcogenides (TMDs), thermal conductivity becomes smaller as it goes from graphite to TMDs to TMPS3, and the difference is larger at low temperature, e.g., around 50 K. From the Callaway model analysis, we could attribute the large thermal conductivity reduction for TMPS3, particularly at low temperature, to the phonon scattering from the boundary. We actually confirmed the existence of the large population of the stacking faults with the cross-sectional transmission electron microscopy image of MnPS3. This suggests that intrinsic or extrinsic stacking faults formed in van der Waals materials and their heterostructures can play an important role in reducing the cross-plane thermal conductivity as a source of the boundary scattering. [ABSTRACT FROM AUTHOR]

We investigate the Dzyaloshinskii–Moriya interaction (DMI) and spin–orbit torque effects in CuIr/CoFeB/MgO heterostructures. To this end, harmonic Hall measurements and current induced domain wall motion experiments are performed. The motion of domain walls at zero applied field due to current demonstrates the presence of DMI in this system. We determine the strength of the DMI to be D = + 5 ± 3 μ J / m 2 and deduce right-handed chirality in domain walls showing a partial Néel type spin structure. To ascertain the torques, we perform a second harmonic measurement to quantify the damping- and field-like current induced effective fields as a function of the magnetization direction. From the angular dependent analysis, we identify non-negligible higher order terms for polar magnetization angles θ > 0 , which need to be included when considering the effective manipulation of spins by current. [ABSTRACT FROM AUTHOR]

The magnetofluctuation conductivity, called excess conductivity, originated from the forming of the superconducting droplet near to the mean-field transition temperature, was measured for the optimally doped BaFe1.8Co0.2As2 single crystals with a critical temperature, Tc, of 24.6 K. This measurement of the excess conductivity for magnetic fields up to 9 T was compared with the thermodynamic scaling theory in the critical region, in which not only the Gaussian fluctuation but also fourth order terms of the order parameter are included. An analysis of the excess conductivity showed that the superconductivity followed three-dimensional scaling rather than two-dimensional scaling even though the sample had a layered structure. [ABSTRACT FROM AUTHOR]

Up to now, the vortex avalanche is known to depend critically on the changing of some external parameters, such as the applied magnetic field, the temperature, and the demagnetization factor. In this study, we found the sweeping rate (SR) of the applied magnetic field to be another parameter that contributed to the appearance of the vortex avalanche. For example, a fast SR 500 Oe/s enhanced the vortex avalanche quietly compared to the case of a slow SR of 3 Oe/s. The dependence of the appearance of the vortex avalanche on the SR was quite strong, especially at low temperatures. A H-T phase diagram that distinguishes the regions of magnetic stability and instability is drawn for each SR. [ABSTRACT FROM AUTHOR]

The intrinsic origin of the ferromagnetic ordering in Zn1-xMnxO thin films grown by pulsed-laser deposition was investigated. The ferromagnetic behaviors for a Zn1-xMnxO (x=0.26) film grown at 700 °C under oxygen pressures of 10-1 Torr were observed at 4 and 300 K. The anomalous Hall effect (AHE) was found at temperatures of up to 210 K for the Zn0.74Mn0.26O thin film. The anomalous Hall coefficients (RA) were determined to be approximately proportional to the square of resistivity in the low field region, indicating the side-jump process for the AHE. Our results provide direct experimental evidence that a carrier-mediated mechanism is responsible for the ferromagnetic ordering in Zn1-xMnxO thin films grown by pulsed-laser deposition. [ABSTRACT FROM AUTHOR]

The electronic structures of the magnetic topological insulator candidates of Ce-substituted Bi2–xCexSe3 (x ≤ 0.12) have been investigated through angle-resolved photoemission spectroscopy (ARPES), soft X-ray absorption spectroscopy (XAS), and soft X-ray magnetic circular dichroism (XMCD) measurements on high-quality single crystals. Ce 3d XAS and XMCD measurements provide evidence that the substituted Ce ions in Bi2–xCexSe3 are trivalent and magnetic, confirming the purely magnetic effect of the Ce-substitution. ARPES measurements reveal the formation of an energy gap (Δ) for x > 0, indicating that the finite Δ arises from the broken time-reversal symmetry due to the substituted magnetic Ce impurities. [ABSTRACT FROM AUTHOR]

We report the structural, magnetic, and electrical properties of antiferromagnetic cubic Mn3Ga thin films, in comparison with ferrimagnetic tetragonal Mn3Ga. The structural analyses reveal that cubic Mn3Ga is heteroepitaxially grown on a MgO substrate with a disordered Cu3Au-type cubic structure, which transforms to tetragonal Mn3Ga as the RF sputtering power increases. In cubic Mn3Ga, the Mn moments aligned ferromagnetically in layers are stacked antiferromagnetically between layers, compared to the theoretical prediction. The magnetic and magnetotransport data show the antiferromagnetic transition at TN = 400 K for cubic Mn3Ga and the ferrimagnetic transition at TC = 820 K for tetragonal Mn3Ga. Furthermore, we find that the antiferromagnetic cubic Mn3Ga exhibits a higher electrical resistivity than the ferrimagnetic tetragonal Mn3Ga, which can be understood by the spin-dependent scattering mechanism. [ABSTRACT FROM AUTHOR]

We investigated the spin wave dynamics of CoFeSiB film, which has a stripe domain structure at a low magnetic field region (<1 kOe). We measured the spin wave excitation spectra by employing Brillouin light scattering. Abnormal field dependence and dispersion relations were observed, and they are similar to spin wave quantization in laterally confined magnetic structures such as arrays of magnetic nanowires. The observed spin wave excitation spectra must be interpreted with spin wave quantization such as Damon–Eshbach mode separation. It was found that the spin wave quantization is related to the stripe magnetic domain structure in continuous film. The physical origin of the quantization is the partial reflection of the propagating spin wave at the periodic stripe domain boundaries. [ABSTRACT FROM AUTHOR]

It is generally accepted that Bi2Te3 prepared from stoichiometric melts has p-type charge carriers generated from BiTe-type antisite defects, while Bi2Te3 grown under Te-rich condition becomes n-type due to another type of TeBi antisite defects. We report the magnetic and transport properties of GdxBi2-xTe3 prepared from stoichiometric melts, where p-type charge carriers are dominant. The physical properties of all the samples have no significant changes with varying the nominal Gd composition up to x = 0.2. Compared with n-type GdxBi2-xTe3 samples grown under Te-rich condition, we find low solubility for all the samples and no clear signature of antiferromagnetic order. These results suggest that the Gd doping rate in GdxBi2-xTe3 is governed by the type of antisite defects and charge carriers, so that the antiferromagnetic ordering is not eventually introduced. [ABSTRACT FROM AUTHOR]

Magnetically doped topological insulators have been significantly researched for unlocking the nontrivial topological phases and the resultant potential applications for spintronics. We report the effect of antiferromagnetic order induced by Gd substitution on the electronic properties of GdxBi2−xSe3 single crystals by analyzing the Shubnikov-de Haas oscillations. Antiferromagnetic order of Gd ions affects the 2D surface state in Bi2Se3 and changes the effective mass and lifetime of charge carriers. These observations suggest a strong correlation of 2D surface electrons with the antiferromagnetic ordering, where the itinerant electrons are bound to the Gd ions to mediate the antiferromagnetic interaction. [ABSTRACT FROM AUTHOR]

The ferromagnetic layer in magnetic tunnel junctions (MTJs) was oxidized with varying O2 concentrations, and the corresponding effect on spin-dependent transport was studied. As expected from our previous results for MTJs with an over-oxidized AlOx tunnel barrier, a partially oxidized ferromagnetic layer plays an important role in spin-dependent transport. As the temperature is lowered, the junction resistance increases dramatically, and the tunneling magnetoresistance (TMR) is strongly suppressed. Increasing the O2 concentration enhances the increase of resistance and suppression of TMR. This work supports our previous conclusion that oxidizing the ferromagnetic layer generates localized magnetic moments, which act as a scattering center for spin-polarized tunneling electrons. [ABSTRACT FROM AUTHOR]

We recently reported that spin transfer torque switching current density is very sensitive to the junction sizes and the exchange stiffness constants of the free layer, based on micromagnetic simulations. The results are very complicated and far from the simple macro-spin model because of the non-coherent spin switching processes. The dependence of switching current density on junction sizes and the exchange stiffness constants becomes systematic when we employ the non-collinear polarizer layer. We found that the non-collinear polarizer layer enhances the coherency of the spin dynamics by breaking symmetric spin configurations and causes noticeable reductions in the switching current density. [ABSTRACT FROM AUTHOR]

We investigated the perpendicular magnetic anisotropy of amorphous CoSiB/Pd multilayer systems. We replaced the crystalline Co layer with an amorphous CoSiB layer in a Co/Pd multilayer system in order to reduce the domain wall pinning sites, which are mainly located at the grain boundaries and interfaces. We also found the correlation between the coercivity and the thermal activation volume of the magnetization reversal in the amorphous CoSiB/Pd multilayers. The time-dependent magnetization reversal was investigated using the magneto-optical Kerr effect image and the magnetic field sweep-rate-dependent coercivity. [ABSTRACT FROM AUTHOR]

We investigate the dependence of switching current density on the junction sizes in the in-plane spin transfer torque nanopillar structures by using micromagnetic simulations. While the macrospin model predicts weak dependence of switching current density on the junction sizes, we find that the switching current density is a sensitive function of the junction sizes. It can be explained with the complicated spin configurations and dynamics during the switching process. The detail spin configurations and dynamics are determined by spin wave excitation with the finite wave vector, which is related with the exchange coupling energy and junction shape. [ABSTRACT FROM AUTHOR]

The effects of magnetic doping on a EuB6 single crystal were investigated based on magnetic and transport measurements. A modest 5% Sm substitution for Eu changes the magnetic and transport properties dramatically and gives rise to concurrent antiferromagnetic and metal-insulator transitions (MITs) from ferromagnetic MIT for EuB6. Magnetic doping simultaneously changes the itinerant carrier density and the magnetic interactions. We discuss the origin of the concurrent magnetic MIT in Eu1-xSmxB6. [ABSTRACT FROM AUTHOR]

This paper dealt with the electrical properties of Ga:ZnO film deposited via pulsed laser deposition and the mechanisms responsible for conduction and scattering behavior in terms of temperature. Such film having a degenerate band exhibited the metallic characteristics except those observed below 100 and 60 K for films fabricated at 298 and 773 K, respectively. This metal semiconductor transition (MST) was explained based on weakly localized electrons found in disorder conductor. It was found that the predominant scattering mechanism was ionized-impurity scattering below MST region, while lattice vibration and grain boundary scattering were important in the regime above MST temperature. [ABSTRACT FROM AUTHOR]

The authors investigated the magnetic and ferroelectric properties of hexagonally grown HoMnO3 thin films. The magnetic measurements revealed bulklike magnetic phase transitions with an additional spin-glass-like behavior feature below the Néel temperature. The ferroelectricity in the films was distinctly different from the suggested bulk behavior. Below 40 K, the HoMnO3 films showed typical ferroelectric character: their remnant polarization and coercive field values at 20 K were 3.7 μC/cm2 and 0.69 MV/cm. Above 40 K, however, the films exhibited an unusual antiferroelectriclike behavior, with more pronounced features appearing at higher temperatures. These intriguing physical properties make HoMnO3 films a potential candidate material for numerous future applications. [ABSTRACT FROM AUTHOR]

Mixture of single-crystalline MnO and Mn3O4 nanowires was synthesized by thermal evaporation of MnCl2 powders. The diameter is 50–100 nm, the length is about 20 μm, and the growth direction is uniformly [100] for both cubic MnO and tetragonal Mn3O4 nanowires. The temperature-dependent magnetization and magnetic hysteresis curves suggest the Curie temperature of 12 and 43 K for the MnO and Mn3O4 nanowires, respectively. [ABSTRACT FROM AUTHOR]

We report the dramatic change of gapless semiconductor properties by different chemical doping elements of Co and Mn into PbPdO2. The metal-insulatorlike transition temperature TMI = 100 K for PbPdO2 shifts to a higher temperature of 150 K by the Co doping and to a lower temperature of 70 K by the Mn doping. Because of the anisotropic band structure with the majority of heavy holes and the minority of light electrons, the transport and magnetic properties are significantly changed by the chemical doping elements. At low temperatures, the Co doping enhances ferromagnetic interactions, whereas the Mn doping favors antiferromagnetic interactions. These results are of great interests because you can control the magnetic ordering as well as manipulate the carrier density by changing the doping elements. These materials could be a good candidate for spintronics applications. [ABSTRACT FROM AUTHOR]

A correction to the article "A reconstruction of cubic rs-ZnO on MgO (200) substrate through (100) plane of w-ZnO:rs-ZnO for transparent electronic application" in a previous issue is presented.

The electronic structures of the magnetic topological insulator candidates of Ce-substituted Bi2–xCexSe3 (x ≤ 0.12) have been investigated through angle-resolved photoemission spectroscopy (ARPES), soft X-ray absorption spectroscopy (XAS), and soft X-ray magnetic circular dichroism (XMCD) measurements on high-quality single crystals. Ce 3d XAS and XMCD measurements provide evidence that the substituted Ce ions in Bi2–xCexSe3 are trivalent and magnetic, confirming the purely magnetic effect of the Ce-substitution. ARPES measurements reveal the formation of an energy gap (Δ) for x > 0, indicating that the finite Δ arises from the broken time-reversal symmetry due to the substituted magnetic Ce impurities. [ABSTRACT FROM AUTHOR]