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The crystal structure, cryogenic magnetic properties, and magnetocaloric performance of double perovskite Eu2NiMnO6 (ENMO), Gd2NiMnO6 (GNMO), and Tb2NiMnO6 (TNMO) ceramic powder samples synthesized by solid-state method have been investigated. X-ray diffraction structural investigation reveal that all compounds crystallize in the monoclinic structure with a P21/n space group. A ferromagnetic to paramagnetic (FM-PM) second-order phase transition occurred in ENMO, GNMO, and TNMO at 143, 130, and 112 K, respectively. Maximum magnetic entropy changes and relative cooling power with a 5 T applied magnetic field are determined to be 3.2, 3.8, 3.5 J/kgK and 150, 182, 176 J/kg for the investigated samples, respectively. The change in structural, magnetic, and magnetocaloric effect attributed to the superexchange mechanism of Ni2+–O–Mn3+ and Ni2+–O–Mn4+. The various atomic sizes of Eu, Gd, and Tb affect the ratio of Mn4+/Mn3+, which is responsible for the considerable change in properties of double perovskite.

Nanoscale-layered ferromagnets have demonstrated fascinating two-dimensional magnetism down to atomic layers, providing a peculiar playground of spin orders for investigating fundamental physics an...

Electrical conduction in magnetic materials depends on their magnetization configuration, resulting in various magnetoresistances (MRs). The microscopic mechanisms of MR have so far been attributed to either an intrinsic or extrinsic origin, yet the contribution and temperature dependence of either origin has remained elusive due to experimental limitations. In this study, we independently probed the intrinsic and extrinsic contributions to the anisotropic MR (AMR) of a permalloy film at varying temperatures using temperature-variable terahertz time-domain spectroscopy. The AMR induced by the scattering-independent intrinsic origin was observed to be approximately 1.5% at T = 16 K and is virtually independent of temperature. In contrast, the AMR induced by the scattering-dependent extrinsic contribution was approximately 3% at T = 16 K but decreased to 1.5% at T = 155 K, which is the maximum temperature at which the AMR can be resolved using THz measurements. Our results experimentally quantify the temperature-dependent intrinsic and extrinsic contributions to AMR, which can stimulate further theoretical research to aid the fundamental understanding of AMR.

Double perovskite Eu2NiMnO6 (ENMO) Gd2NiMnO6 (GNMO) and Tb2NiMnO6 (TNMO) ceramic powder have been synthesized by solid-state reaction and their crystal structure, microstructure, cryogenic magnetic properties, and magnetocaloric performance have been investigated. Structural studies by using X-ray diffraction shows that all compounds crystallize in the monoclinic structure with a P21/n space group. A ferromagnetic to paramagnetic (FM-PM) second-order phase transition occurred in ENMO, GNMO, and TNMO around 143, 130, and 112 K, respectively. The values of maximum magnetic entropy change and relative cooling power at an applied field of 5 T are found to be 3.2, 3.8, 3.5 J/kgK and 150, 182, 176 J/kg respectively, for the studied sample. The change in structural, magnetic, and magnetocaloric effect ascribed to the superexchange mechanism of Ni2+ – O – Mn3+ and Ni2+ – O – Mn4+. Due to different atomic size of Eu, Gd, Tb changes the ratio of Mn4+/Mn3+ which is responsible for the variation of properties significantly in double perovskite.

Straightforward growth of nanostructured low-bandgap materials is a key issue in mass production for electronic device applications. We report here facile nanowall growth of MoS2-MoSX using sputter deposition and investigate the electronic properties of the nanowalls. MoS2-MoSX nanowalls become gradually thicker and taller, with primarily (100)-plane growth directions, with increasing deposition time. Nanowalls combine with nearby walls when a rapid thermal annealing (RTA, 200 °C–500 °C) process is applied. All samples have conventional low-bandgap semiconductor behavior with exponential resistance increase as measurement temperature decreases. The 750 nm-thick MoS2-MoSX nanowalls have a sheet carrier mobility of up to 2 cm2·V−1·s−1 and bulk carrier concentration of ~1017–1019 cm−3 range depending on RTA temperature. Furthermore, perpendicular field-dependent magnetoresistance at 300 K shows negative magnetoresistance behavior, which displays resistance decay by applying a magnetic field (MR ratio in the −1 % range at 5 T). Interestingly, 400 °C RTA treated samples show a resistance upturn when applying an external magnetic field of more than 3 T. Our research suggests tuneability of MoS2 nanowall size and mesoscopic electronic transport properties.

Spin pumping and the spin transfer torque in the normal metal (NM)/ferromagnetic materials (FM) heterostructure strongly depend on the interfacial spin memory loss. Therefore, the interface engineering of the NM/FM bilayer is important for enhancing spin pumping and spin-orbit torque efficiency for spin-orbitronic devices. In this study, we investigate the influence of the graphene interlayer between Pt and yttrium iron garnet (YIG) on spin pumping. Measurements of both the coplanar wave guide ferromagnetic resonance and inverse spin Hall effect with ferromagnetic resonance are performed to study the role of graphene in the transmission of the spin current at the interface. Results indicate a decreased Gilbert damping constant with the insertion of graphene interlayer, which causes the spin mixing conductance and inverse spin Hall voltage to be significantly reduced. The observed decrease in damping constant and spin injection is attributed to the presence of magnetic proximity effect and interfacial spin-orbit scattering, which causes graphene to serve as a spin-sink layer.

We found new two-dimensional (2D) quantum (S=1/2) antiferromagnetic systems: CuRE2Ge2O8 (RE=Y and La). According to our analysis of high-resolution X-ray and neutron diffraction experiments, the Cu-network of CuRE2Ge2O8 (RE=Y and La) exhibits a 2D triangular lattice linked via weak bonds along the perpendicular b-axis. Our bulk characterizations from 0.08 to 400 K show that they undergo a long-range order at 0.51(1) and 1.09(4) K for the Y and La systems, respectively. Interestingly, they also exhibit field induced phase transitions. For theoretical understanding, we carried out the density functional theory (DFT) band calculations to find that they are typical charge-transfer-type insulators with a gap of Eg = 2 eV. Taken together, our observations make CuRE2Ge2O8 (RE=Y and La) additional examples of low-dimensional quantum spin triangular antiferromagnets with the low-temperature magnetic ordering.

The magnetic resonance of Fe nanoparticles has been observed in single-crystal Fe/MgO/Fe magnetic tunnel junctions (MTJs). In the MTJs, one magnetic layer is a continuous Fe film, which acts as a magnetic reference layer, and the other is made up of noncontinuous nanoparticles of Fe, which act as a free layer. The magnetic resonance is electrically excited by the spin torque and is detected as the homodyne detection voltage, which is called the spin-torque diode effect. From the magnetoresistance characteristics, the average diameter of the Fe nanoparticles is estimated to be 6.8 nm; these nanoparticles exhibit superparamagnetic behavior at room temperature. This spin-torque magnetic resonance in magnetic nanoparticles enables us to study the magnetization dynamics in small spin systems.

Hybrid nanoparticles of LiFePO4 with carbon and lithium phosphates were synthesized through organic–inorganic co-assembly procedure using a triblock copolymer (F108 or P123). We found that the triblock copolymers play a critical role in controlling size of hybrid particle and the degree of crystallinity of the inorganic nanostructures. The hybrid using P-123 had more graphitic carbon which resulted in fast electron mobility. Also, magic angle spinning nuclear magnetic resonance (MAS-NMR) revealed that the crystallinity of the hybrid using P123 is higher than that using F108 which is not measurable in X-ray diffraction. Electrochemical performance of the hybrid using P123 as a cathode material in Li-ion batteries showed superior rate capability at 20 C of charging rate and 2 C of discharging rate without capacity loss, in which discharge capacity was 102 mAh/g.

The existence and feasibility of the multicaloric, polycrystalline material 0.8Pb(Fe1/2Nb1/2)O3-0.2Pb(Mg1/2W1/2)O3, exhibiting magnetocaloric and electrocaloric properties, are demonstrated. Both the electrocaloric and magnetocaloric effects are observed over a broad temperature range below room temperature. The maximum magnetocaloric temperature change of ~0.26 K is obtained with a magnetic-field amplitude of 70 kOe at a temperature of 5 K, while the maximum electrocaloric temperature change of ~0.25 K is obtained with an electric-field amplitude of 60 kV/cm at a temperature of 180 K. The material allows a multicaloric cooling mode or a separate caloric-modes operation depending on the origin of the external field and the temperature at which the field is applied.

Spin-transfer torque allows the magnetization of nanopillar devices to be switched electrically. Incorporating asymmetries into the design of such a device generates a linear out-of-plane torque component that could help prevent the unwanted spontaneous reversal of the nanopillar’s magnetization. Spin-transfer torque1,2 (STT) allows the electrical control of magnetic states in nanostructures3,4,5. The STT in magnetic tunnel junctions (MTJs) is of particular importance owing to its potential for device applications6,7. It has been demonstrated8,9,10,11 that the MTJ has a sizable perpendicular STT ( , field-like torque), which substantially affects STT-driven magnetization dynamics. In contrast to symmetric MTJs where the bias dependence of is quadratic8,9,10,12,13, it is theoretically predicted that the symmetry breaking of the system causes an extra linear bias dependence11. Here, we report experimental results that are consistent with the predicted linear bias dependence in asymmetric MTJs. The linear contribution is quite significant and its sign changes from positive to negative as the asymmetry is modified. This result opens a way to design the bias dependence of the field-like term, which is useful for device applications by allowing, in particular, the suppression of the abnormal switching-back phenomena.

Work at Korea Advanced Institute of Science and Technology (KAIST) was supported through the Creative Research Institute Project and the Cavendish-KAIST Cooperation Project of the Korean Ministry of Science and Technology and Works at SungKyunKwan University were supported by he BK21 program, the 21st Century Frontier R&D Pro- gram for Hydrogen Energy and the Basic Atomic Energy Research Institute program.

TbMnO3 exists in an orthorhombic phase in nature. Recently, we successfully grew TbMnO3 thin films in the hexagonal phase using epitaxial stabilization techniques. In this article, we will show the details of the deposition conditions that allow us to fabricate the hexagonal TbMnO3 films on Pt–Al2O3(0001) substrates. The artificial hexagonal phase can be easily formed above 850 °C, irrespective of the oxygen partial pressure. The hexagonal TbMnO3 films showed ferroelectric properties, which are significantly enhanced compared to those of the orthorhombic TbMnO3 bulk phase. We find interesting anomalies in the magnetic and magnetodielectric properties of the TbMnO3 films at around 45 K, which should be related with the Mn3+ spin reorientation. We also find spin-glass-like behaviors in the magnetic susceptibility, which could be attributed to the geometric frustration of antiferromagnetically coupled Mn spins with an edge-sharing triangular lattice. This work shows details of the growth and properties of hexagonal TbMnO3 films.

The phenomena based on spin-orbit interaction in heavy metal/ferromagnet/oxide structures have been investigated extensively due to their applicability to the manipulation of the magnetization direction via the in-plane current. This implies the existence of an inverse effect, in which the conductivity in such structures should depend on the magnetization orientation. In this work, we report a systematic study of the magnetoresistance (MR) of W/CoFeB/MgO structures and its correlation with the current-induced torque to the magnetization. We observe that the MR is independent of the angle between the magnetization and current direction but is determined by the relative magnetization orientation with respect to the spin direction accumulated by the spin Hall effect, for which the symmetry is identical to that of so-called the spin Hall magnetoresistance. The MR of ~1% in W/CoFeB/MgO samples is considerably larger than those in other structures of Ta/CoFeB/MgO or Pt/Co/AlOx, which indicates a larger spin Hall angle of W. Moreover, the similar W thickness dependence of the MR and the current-induced magnetization switching efficiency demonstrates that MR in a non-magnet/ferromagnet structure can be utilized to understand other closely correlated spin-orbit coupling effects such as the inverse spin Hall effect or the spin-orbit spin transfer torques.

We investigate the origin of insulating weak-ferromagnetic phase in ultra-thin epitaxial La0.67Sr0.33MnO3 (LSMO) films on SrTiO3 substrate using density functional theory calculation together with X-ray linear dichroism (XLD). The calculations show that symmetry breaking of the crystal field at the LSMO surface largely lowers the energy level of Mn d3z2 orbital at the surface and leads to full occupancy of the d3z2 orbital in majority spin channel, and XLD spectra clearly show the preferential occupation of Mn d3z2 orbital at the surface. Such an orbital reconstruction and charge redistribution in the ultra-thin films largely suppresses double-exchange interaction and favors super-exchange interaction, resulting in G-type antiferromagnetic spin ordering and insulating state. The anisotropic exchange interaction due to spin-orbital interaction leads to spin canting, and thus the films show weak ferromagnetism.

Understanding the interplay between spin and heat is a fundamental and intriguing subject. Here we report thermal spin injection and accumulation in CoFe/MgO/n-type Ge contacts with an asymmetry of tunnel spin polarization. Using local heating of electrodes by laser beam or electrical current, the thermally-induced spin accumulation is observed for both polarities of the temperature gradient across the tunnel contact. We observe that the magnitude of thermally injected spin signal scales linearly with the power of local heating of electrodes, and its sign is reversed as we invert the temperature gradient. A large Hanle magnetothermopower (HMTP) of about 7.0% and the Seebeck spin tunneling coefficient of larger than 0.74 meV K(-1) are obtained at room temperature.

We first report the all-electrical spin injection and detection in CoFe/MgO/moderately doped n-Ge contact at room temperature (RT), employing threeterminal Hanle measurements. A sizable spin signal of ~170 k{\Omega} {\mu}m^2 has been observed at RT, and the analysis using a single-step tunneling model gives a spin lifetime of ~120 ps and a spin diffusion length of ~683 nm in Ge. The observed spin signal shows asymmetric bias and temperature dependences which are strongly related to the asymmetry of the tunneling process., Comment: 28 pages, 5 figures

Combined measurements of normal and inverted Hanle effects in CoFe/MgO/semiconductor (SC) contacts reveal the effect of spin relaxation rate on the interfacial spin depolarization (ISD) from local magnetic fields. Despite the similar ferromagnetic electrode and interfacial roughness in both CoFe/MgO/Si and CoFe/MgO/Ge contacts, we have observed clearly different features of the ISD depending on the host SC. The precession and relaxation of spins in different SCs exposed to the local fields from more or less the same ferromagnets give rise to a notably different ratio of the inverted Hanle signal to the normal one. At room temperature, a large ISD is observed in the CoFe/MgO/Si contact, but a small ISD in the CoFe/MgO/Ge contact. The ISD of the CoFe/MgO/Ge contact has been substantially increased at low temperature. These results can be ascribed to the difference of spin relaxation in host SCs. A model calculation of the ISD, considering the spin precession due to the local field and the spin relaxation in the host SC, explains the temperature and bias dependence of the ISD consistently., Comment: 23 pages, 6 figures

We investigated the pinning dominated domain-wall dynamics under an ac field by studying the frequency $(f)$ dependence of hysteresis loops of a uniaxial ferroelectric (FE) system. We measured the fully saturated polarization-electric field $(P\text{\ensuremath{-}}E)$ hysteresis loops of high-quality epitaxial 100-nm-thick ${\text{PbZr}}_{0.2}{\text{Ti}}_{0.8}{\text{O}}_{3}$ capacitors at various $f$ (5--2000 Hz) and temperatures $T$ (10--300 K). We observed that the coercive field ${E}_{C}$ is proportional to ${f}^{\ensuremath{\beta}}$ with two scaling regions, which was also reported earlier in magnetic systems [T. A. Moore and J. A. C. Bland, J. Phys.: Condens. Matter 16, R1369 (2004), and references therein]. In addition, we observed that the two scaling regions of ${E}_{C}$ vs $f$ exist at all measured $T$. We found that the existence of the two scaling regions should come from a dynamic crossover between the creep and flow regimes of the FE domain-wall motions. By extending the theory of Nattermann et al., which was originally proposed for impure magnet systems [T. Nattermann, V. Pokrovsky, and V. M. Vinokur, Phys. Rev. Lett. 87, 197005 (2001)], to the disordered FE systems, we obtained analytical expressions for the dynamic crossovers between the relaxation and creep, and between the creep and flow regimes. By comparing with the experimental data from our fully saturated $P\text{\ensuremath{-}}E$ hysteresis loop measurements, we could construct a $T\text{\ensuremath{-}}E$ dynamic phase diagram with $f$ as a parameter for hysteretic FE domain dynamics in the presence of an ac field.

A stoichiometric ${\text{Tm}}_{5}{\text{Si}}_{2.0\ifmmode\pm\else\textpm\fi{}0.1}{\text{Ge}}_{2.0\ifmmode\pm\else\textpm\fi{}0.1}$ single crystal was grown using the Bridgeman method and was examined by x-ray diffraction, energy dispersive spectroscopy, magnetization, ac and dc magnetic susceptibilities, specific heat, electrical resistivity, and x-ray photoemission spectroscopy experiments. ${\text{Tm}}_{5}{\text{Si}}_{2.0\ifmmode\pm\else\textpm\fi{}0.1}{\text{Ge}}_{2.0\ifmmode\pm\else\textpm\fi{}0.1}$ was found to crystallize with an orthorhombic ${\text{Sm}}_{5}{\text{Ge}}_{4}$-type structure. The mean valence of Tm ions in ${\text{Tm}}_{5}{\text{Si}}_{2.0\ifmmode\pm\else\textpm\fi{}0.1}{\text{Ge}}_{2.0\ifmmode\pm\else\textpm\fi{}0.1}$ was almost trivalent. The $4f$ states were split by the crystalline electric field. The ground state exhibited long-range antiferromagnetic order along the $b$ axis below 8.01 K with the ferromagnetically coupled magnetic moments in the $ac$ plane, whereas the exited states showed a reduced magnetic moment and magnetic entropy and $\ensuremath{-}\text{log}\text{ }T$ behaviors.

We report in this paper the unconventional bias and temperature dependence of the Hanle effect in a highly ordered CoFe/MgO/n-Si contact investigated by means of a three-terminal Hanle method. The spin signal and the effective spin lifetime obtained in this system show non-monotonic behavior with bias and temperature variations. Interestingly, the sign of the spin signal changes significantly with the bias voltage at a low temperature. The sign inversion is presumably ascribed to the contribution of interfacial resonant states formed at the CoFe/MgO interface or bound states in the Si surface during the spin extraction process.

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.

It is known that MgB2 thin films synthesized by using hybrid physical chemical vapor deposition (HPCVD) do not show dendritic avalanche, which is in contrast to those prepared by using pulsed laser deposition (PLD). To find the cause that makes the difference between the two cases, we studied the microscopic film structure by the scanning electron microscopy and the magnetic hysteresis by using the superconducting quantum interference device magnetometry. The critical current density (Jc), estimated from the magnetic hysteresis based on the Bean’s critical-state model, shows a much higher Jc in the PLD film than in a HPCVD film. This indicates higher vortex pinning in the PLD film. We surmise that high local joule heating beyond the high Jc in the PLD film, as a vortex penetrates into the superconducting thin film, gives a path for the next vortex and induces a positive feedback effect that is absent in the HPCVD film.

We fabricated epitaxial (1-x)BiFeO3-xBaTiO3 (x = 0.1-0.7) solid solution films on niobium doped SrTiO3(001) substrate. The x-ray diffraction analysis of the films indicates compressively strained growth for the composition x

Utilizing a systematic study of transport measurements, we constructed a detailed H–T phase diagram of an MgB2 single crystal. There was no tricritical point of the surface superconductivity, the bulk superconductivity and the peak effect, in contrast to the existence of this point in Nb single crystals, as obtained from the magnetic susceptibility. We found that the surface effect was still strong up to the zero-field superconducting transition temperature and that the peak effect did not disappear on the Hc2 line because a disordered flux flow was present just below Hc2. The disappearance of the peak effect is closely related to thermal fluctuations.

The authors investigated the magnetic and ferroelectric properties of hexagonally grown HoMn O3 thin films. The magnetic measurements revealed bulklike magnetic phase transitions with an additional spin-glass-like behavior feature below the N�el temperature. The ferroelectricity in the films was distinctly different from the suggested bulk behavior. Below 40 K, the HoMn O3 films showed typical ferroelectric character: their remnant polarization and coercive field values at 20 K were 3.7 ?C cm2 and 0.69 MVcm. Above 40 K, however, the films exhibited an unusual antiferroelectriclike behavior, with more pronounced features appearing at higher temperatures. These intriguing physical properties make HoMn O3 films a potential candidate material for numerous future applications. � 2007 American Institute of Physics.