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Orbital currents play a fundamental role in a wide range of transport phenomena. Recently, the discovery of a novel chiral orbital current state in the ferrimagnetic nodal-line semiconductor Mn3Si2Te6 has attracted significant interest, supported by anomalous I–V characteristics and time-dependent bistable switching. However, the direct experimental verifications, combining electrical transport and magnetic measurement, that detect the variation of the magnetic properties vs the current are still rare. Here, we investigate the transport properties of Mn3Si2Te6 and track the current-induced dynamics of the magnetic moment. Reflective magnetic circular dichroism reveals that significant alterations in Mn3Si2Te6 magnetoresistance in response to an electric field are necessarily coupled with a magnetic phase transition, establishing a rare correlation. Our findings indicate the predominance of magnetic chiral orbital currents in the colossal angular magnetoresistance effect, offering a unique platform for advanced studies in orbital magnetism. [ABSTRACT FROM AUTHOR]

The magnetic anisotropy of strontium ferrite (SF)/PA12 filament, a popular hard magnetic ferrimagnetic composites that is used for 3D-printing of permanent magnets, is studied by vibrating sample magnetometry. The studied filaments have a composition of SF/PA-12 thermoplastic composite with a 40% wt. ratio of SF. SF particles are non-spherical platelets with an average diameter of 1.3 um and a diameter to thickness ratio of 3. Filaments are produced by a twin-screw extruder and have a diameter of 1.5 mm. SEM images show that the SF particles are homogeneously distributed through the filament. VSM measurements on different parts of the filaments show that the outer part of the cylindrical filament has a higher anisotropy, and the core is mostly isotropic. This conclusion is consistent with computational work by others which suggest that particle alignment predominantly takes place near the walls of the extruder die where shear flow is maximum. Additional hysteresis curve measurement of the outer cylindrical part of the filament parallel to the r and ϕ directions indicates that the squareness of the hysteresis curve (S) is larger in the r-direction. This indicates that the outer surface of the filament has a strong easy axis in the r-direction. We conclude that the SF platelets line up parallel to the walls of the extrusion die. [ABSTRACT FROM AUTHOR]

The accelerating use of organic dyes in various industries has led to a surge in water pollution, especially from non-biodegradable dye effluents discharged into water resources. This study addresses the critical issue of catalyzing the reduction of two prevalent dyes, methylene blue (MB) and rhodamine-B (RhB), using a multiwalled carbon nanotube-cobalt ferrite (MWCNT-CF) nanocomposite. The synthesized nanocomposite demonstrates exceptional catalytic activity, stability, and recyclability. Conventional methods for treating dye-containing wastewater often prove expensive. This study explores the efficacy of catalytic reduction, a relatively fast process facilitated by semiconductor nanoparticles. Structural analyses using X-ray diffraction and high-resolution transmission electron microscopy (HRTEM) confirm the formation of the nanocomposite, revealing unsaturated surface bonds and chains conducive to adsorption. The nanocomposite exhibits a remarkable reduction in both dyes, with easy recyclability for multiple cycles. Magnetization studies confirm the ferrimagnetic nature of the nanocomposite, facilitating its efficient separation from the reaction mixture using a magnet. The study delves into the kinetics of the catalytic reduction following pseudo-first-order kinetics. The surface modifications of the nanocomposite, as revealed by TEM, contribute to enhanced adsorption and catalytic efficiency. Notably, the MWCNT-CF nanocomposite demonstrates negligible loss of catalytic activity during recycling, highlighting its potential for cost-effective and sustainable applications in dye reduction across various industries. [ABSTRACT FROM AUTHOR]

Spin–orbit torques (SOTs) provide an efficient way to electrically manipulate the magnetic order in spintronic devices. Compared with conventional ferromagnetic materials, ferrimagnetic materials have the advantages of antiferromagnetically coupled sublattices and induced ultrafast spin dynamics. In this paper, we study the current-induced magnetization switching in the ferrimagnetic Ta/GdFeCo/MgO system. Robust SOT-induced magnetization switching can be achieved at the magnetic compensation temperature point of around 70 K, where the magnetization is nearly zero and the coercivity can reach almost 3 T. The temperature dependence of the SOT efficiency is quantified by the second harmonic method, and the enhanced SOT efficiency near the magnetic compensation temperature is attributed to the negative exchange coupling between the two sublattices of CoFe and Gd. This work demonstrates the SOT switching of the nearly compensated ferrimagnet, with great potential for future magnetic interaction-free and ultrafast ferrimagnetic applications. [ABSTRACT FROM AUTHOR]

Bimagnetic nanoparticles show promise for applications in energy efficient magnetic storage media and magnetic device applications. The magnetic properties, including the exchange bias of nanostructured materials can be tuned by variation of the size, composition, and morphology of the core vs overlayer of the nanoparticles (NPs). The purpose of this study is to investigate the optimal synthesis routes, structure and magnetic properties of novel CoO/NiFe2O4 heterostructured nanocrystals (HNCs). In this work, we aim to examine how the size impacts the exchange bias, coercivity and other magnetic properties of the CoO/NiFe2O4 HNCs. The nanoparticles with sizes ranging from 10 nm to 24 nm were formed by synthesis of an antiferromagnetic (AFM) CoO core and deposition of a ferrimagnetic (FiM) NiFe2O4 overlayer. A highly crystalline magnetic phase is more likely to occur when the morphology of the core-overgrowth is present, which enhances the coupling at the AFM-FiM interface. The CoO core NPs are prepared using thermal decomposition of Co(OH)2 at 600 °C for 2 hours in a pure argon atmosphere, whereas the HNCs are obtained first using thermal evaporation followed by hydrothermal synthesis. The structural and morphological characterization made using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and scanning electron microscopy (SEM) techniques verifies that the HNCs are comprised of a CoO core and a NiFe2O4 overgrowth phase. Rietveld refinement of the XRD data shows that the CoO core has the rocksalt (Fd3 m) crystal structure and the NiFe2O4 overgrowth has the spinel (C12/m1) crystal structure. SEM-EDS data indicates the presence and uniform distribution of Co, Ni and Fe in the HNCs. The results from PPMS magnetization measurements of the CoO/NiFe2O4 HNCs are discussed herein. [ABSTRACT FROM AUTHOR]

We have carried out joint theoretical and experimental investigations of three Heusler compounds CoMoFeAl, CoMo0.5Fe1.5Al, and Co1.5Mo0.5FeAl. Our first-principle calculations show that all three compounds show either ferro- or ferrimagnetic order with CoMoFeAl and CoMo0.5Fe1.5Al exhibiting high spin polarization of almost 80%. The investigated samples were prepared using arc melting and high vacuum annealing. All the samples show cubic crystal structure with disorder. The parent compound CoMoFeAl shows a small saturation magnetization of 12 emu/g, and a Curie temperature of 440 K. The other two compounds, namely, Co1.5Mo0.5FeAl and CoMo0.5Fe1.5Al, show much higher saturation magnetizations of 62 emu/g and 59 emu/g, and substantially higher Curie temperatures of 950 K and 780 K, respectively. [ABSTRACT FROM AUTHOR]

In this work, we investigate the synthesis, along with the structural and magnetic properties, of novel Mn-Co-NiO-based heterostructured nanocrystals (HNCs). The objective is to develop novel, well-structurally ordered inverted antiferromagnetic (AFM) NiO–ferrimagnetic (FiM) spinel phase overgrowth HNCs. Inverted HNCs are particularly promising for magnetic device applications because their magnetic properties are more easily controlled by having well-ordered AFM cores, which can result in magnetic structures having large coercivities, tunable blocking temperatures, and other enhanced magnetic effects. The synthesis of the HNCs is accomplished using a two-step process: In the first step, NiO nanoparticles are synthesized using a thermal decomposition method. Subsequently, Mn-Co overgrowth phases are grown on the NiO nanoparticles via hydrothermal nanophase epitaxy, using a fixed pH level (∼5.3) of the aqueous medium. This pH level was selected based on previous work in our laboratory showing that NiO/Mn3O4 HNCs of constant size have optimal coercivity and exchange bias when synthesized at a pH of 5.0. The crystalline structure and gross morphology of the Mn-Co-NiO-based HNCs have been analyzed using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) techniques, respectively. Analysis using these techniques shows that the HNCs are composed of a NiO core and a CoMn2O4 overgrowth phase. Rietveld refinement of XRD data shows that the NiO core has the rocksalt (Fm 3 ̄ m) cubic crystal structure and the CoMn2O4 overgrowth has the spinel (I41/amd) crystal structure. Moreover, an increased relative amount of the CoMn2O4 overgrowth phase is deposited with decreasing NiO core particle size during the synthesis of the HNCs. The results from PPMS magnetization and high-resolution transmission electron microscopy (HRTEM) characterization of the Mn-Co-NiO-based HNCs are discussed herein. [ABSTRACT FROM AUTHOR]

Interfacial mixing of elements is a well-known phenomenon found in thin film deposition. For thin-film magnetic heterostructures, interfacial compositional inhomogeneities can have drastic effects on the resulting functionalities. As such, care must be taken to characterize the compositional and magnetic properties of thin films intended for device use. Recently, ferrimagnetic Mn4N thin films have drawn considerable interest due to exhibiting perpendicular magnetic anisotropy, high domain-wall mobility, and good thermal stability. In this study, we employed x-ray photoelectron spectroscopy (XPS) and polarized neutron reflectometry (PNR) measurements to investigate the interfaces of an epitaxially grown MgO/Mn4N/Pt trilayer deposited at 450 °C. XPS revealed the thickness of elemental mixing regions of near 5 nm at both interfaces. Using PNR, we found that these interfaces exhibit essentially zero net magnetization at room temperature. Despite the high-temperature deposition at 450 °C, the thickness of mixing regions is comparable to those observed in magnetic films deposited at room temperature. Micromagnetic simulations show that this interfacial mixing should not deter the robust formation of small skyrmions, consistent with a recent experiment. The results obtained are encouraging in terms of the potential of integrating thermally stable Mn4N into future spintronic devices. [ABSTRACT FROM AUTHOR]

Single-domain Co0.5Cu0.5Fe2O4 ferrite nanoparticles with a crystallite size of 23 nm were hydrothermally prepared and characterized using x-ray diffraction, transmission electron microscopy, Fourier-transform infrared (FT-IR) spectroscopy, and vibrating sample magnetometry. According to the Rietveld refinement results, the prepared nanoparticles were single-phase with spinel type structures. The transmission electron microscope measurements demonstrated that the nanoparticles were spherical in shape. The FT-IR spectrum showed two principle absorption bands, confirming the characteristic features of cubic spinel ferrites. Magnetization data revealed that the prepared nanoparticles were ferrimagnetic from room temperature to 10 K, with well-defined saturation magnetization, coercivity, and remanence magnetization. The remanence magnetization and coercivity were found to increase with decreasing temperature. The value of room temperature squareness ratio (Mr/Ms) of 0.42 was found to be somewhat similar to that expected (0.5) for a system of noninteracting single-domain nanoparticles, suggesting that the prepared nanoparticles are in a single-domain regime. The temperature dependence of coercivity was found to have slight deviations from Kneller's law, possibly due to interactions between nanoparticles. The zero field cooled–field cooled curves indicated that below 150 K, the nanoparticles were ferrimagnetic dressed with spin-glass behavior, resulting from interactions between the ferrimagnetic nanoparticles and/or random freezing of surface spins. [ABSTRACT FROM AUTHOR]

In this study, we have investigated amorphous 20-nm-thick Tb/Fe80Co20 multilayer samples with different individual layer thicknesses and their corresponding alloy counterpart. In particular, the structural and magnetic properties were analyzed upon post-annealing. Up to a certain critical thickness of the individual layers in the multilayer, no significant difference between the multilayers and the alloy is observed in their as-deposited states, which indicates the importance of interfacial intermixing. With a further increase in thicknesses of the individual layers, regions with significant larger Tb content emerge, resulting in a reduced effective Tb moment. The loss in perpendicular magnetic anisotropy upon annealing seems to be delayed for multilayers with thin individual layers compared to the alloy sample. We contribute this behavior to the underlying anisotropic short-range order enforced by the multilayer structure, which hinders the structural relaxation process. At higher temperatures, the multilayers strongly intermix and Fe and Co diffuse through the capping layer. This process leads to a strong enhancement of the saturation magnetization at a certain annealing temperature, due to the formation of separated FeCo and Tb-rich TbFeCo alloy layers, until the sample gets oxidized. [ABSTRACT FROM AUTHOR]

A novel CMOS hexaferrite circulator with a Y-junction structure is designed and fabricated, which is compatible with standard CMOS technology. The spin-coating approach is adopted during the fabrication, in which the photoresist is mixed with nano-hexaferrite powder for preparation of a magnetic thin film in the device. Compared with the traditional circulator with an external permanent magnet for operation, the novel circulator can utilize the spin-coating magnetic film and is compatible with CMOS technology. The remanent magnetization of the adopted hexaferrite thin film can provide the required magnetic field for reciprocity properties. The optimization of impedance matching and the improvements in the related parameters are demonstrated on the novel CMOS circulator. The CMOS circulator exhibits the merits of small volume and easy integration while keeping its promising non-reciprocity properties. The fabrication is conducted based on the standard 180-nm CMOS technology. S-parameter measurements on the circulator show that the device has an isolation of 20 dB over 520 MHz bandwidth at 26.2 GHz. The minimum insertion loss is 1.81 dB. The novel CMOS-compatible circulator has potential application in 5G wireless communication systems. [ABSTRACT FROM AUTHOR]

We investigated the effects of surface modification treatment (SMT) on the perpendicular magnetic anisotropy (PMA) and the thermal tolerance of top-pinned magnetic tunnel junctions (MTJs) with a Co/Pt synthetic ferrimagnetic coupling reference layer. Applying an SMT to the bottom Pt layer increased the PMA of the overlying Co/Pt multilayer. X-ray diffraction spectrum analysis revealed that the SMT resulted in a higher crystallinity and smaller lattice spacing in the Co/Pt multilayer in the thinner bottom Pt layer, which may have increased the PMA in the Co/Pt multilayer. The tunnel magnetoresistance (TMR) ratio of the MTJ with SMT increased as the annealing temperature was increased up to 400 °C; conversely, the TMR ratio of the MTJ without SMT decreased at an annealing temperature of 400 °C. Evaluation of the m-H loops revealed that, after annealing at 400 °C, the reference layers in the MTJs after SMT possessed better magnetic properties than those in the MTJs without an SMT; this is attributable to the higher PMA of the reference layers with SMT. EDX line analysis revealed that SMT suppressed Pt diffusion to the MgO barrier, resulting in a higher thermal tolerance and larger PMA of the reference layer. [ABSTRACT FROM AUTHOR]

Ferrimagnetic alloy thin films that exhibit perpendicular (out-of-plane) magnetic anisotropy (PMA) with low saturation magnetization, such as GdCo and Mn4N, were predicted to be favorable for hosting small Néel skyrmions for room temperature applications. Due to the exponential decay of interfacial Dzyaloshinskii–Moriya interaction and the limited range of spin–orbit torques, which can be used to drive skyrmion motion, the thickness of the ferrimagnetic layer has to be small, preferably under 20 nm. While there are examples of sub-20 nm, rare earth-transition metal (RE-TM), ferrimagnetic thin films fabricated by sputter deposition, to date, rare-earth-free sub-20 nm Mn4N films with PMA have only been reported to be achieved by molecular beam epitaxy, which is not suitable for massive production. Here, we report the epitaxial growth of sub-20 nm Mn4N films with PMA at 400 °C–450 °C substrate temperatures on MgO substrates by reactive sputtering. The Mn4N films were achieved by reducing the surface roughness of MgO substrate through a high-temperature vacuum annealing process. The optimal films showed low saturation magnetization (Ms = 43 emu/cc), low magnetic anisotropy energy (0.7 Merg/cc), and a remanent magnetization to saturation magnetization ratio (Mr/Ms) near 1 at room temperature. Preliminary ab initio density functional theory calculations have confirmed the ferrimagnetic ground state of Mn4N grown on MgO. The magnetic properties, along with the high thermal stability of Mn4N thin films in comparison with RE-TM thin films, provide the platform for future studies of practical skyrmion-based spintronic materials. [ABSTRACT FROM AUTHOR]

This work investigates the microwave absorption property of the ferrimagnetic double perovskite, Sr2FeMoO6 (SFMO) using two different methods: magnetoimpedance (MI) and lock-in based broadband magnetic resonance detection. In the MI method, radio frequency (rf) current (f = 0.001 to 2.8 GHz) is injected into the sample. When dc magnetic field is swept, rf resistance exhibits a single sharp peak centred at H = 0 for f < 0.1 MHz. As f increases, the peak at H = 0 transforms into a dip accompanied by symmetrical double peaks at H = ±HP, which we attribute to the ferromagnetic resonance within the grains. HP increases with increasing frequency of the current. In the lock-in based broadband method the sample, placed on top of a coplanar waveguide, experiences an intense microwave magnetic field from the waveguide, and the field derivative of microwave power absorption is measured as the dc magnetic field is swept. Correlation between MI and microwave power absorption is shown. Landé g factors obtained from both the measurements are close, equal to 2.085, which implies the presence of Fe3+ cations. Large ac magnetoresistance in SFMO compared to its dc value, dominated by the dynamics of transverse permeability and ferromagnetic resonance within grains could be exploited for high-frequency device applications. [ABSTRACT FROM AUTHOR]

Mixed spinel–perovskite multiferroic (1 − x)BaTi0.5Mn0.5O3 + (x)Ni0.6Zn0.4Fe1.85Sm0.15O4 [(1 − x)BTMO + (x)NZFSO] ceramic composites with different concentrations, x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, have been prepared by the effective double sintering ceramic method. X-ray diffraction confirms the coexistence of the cubic spinel structure of the ferrimagnetic phase, Ni0.6Zn0.4Fe1.85Sm0.15O4 (NZFSO), and the tetragonal structure of the ferroelectric phase, BaTi0.5Mn0.5O3 (BTMO), in the composites. The theoretical density decreases while the bulk density increases with the substitution of ferrimagnetic NZFSO into ferroelectric BTMO. Scanning electron microscopy shows an increment in the grain size with ferrite doping. Increasing permeability with ferrite doping indicates the enhancement of magnetic properties of the composites. The Cole–Cole plot affirms the contribution of grains, grain boundaries, and electrodes to the resistive properties of the samples. The variation in polarization and magnetization is correlated with the ferrite content. The composite with x = 0.8 has a high saturation magnetization, Ms = 28.67 emu/g, and has a maximum remanent polarization, Pr = 258.123 µC/cm2. [ABSTRACT FROM AUTHOR]

We investigate the Hf/GdFeCo bilayer with the MgO cap layer for both rare earth (RE)-rich and transition metal (TM)-rich configurations of the ferrimagnetic sublattice in the presence of the perpendicular field. We study the coercivity using the anomalous Hall effect (AHE) technique by multiple measurements on the same sample. In the first set of measurements and at low electric currents, coercivity sharply drops because of the oxygen diffusion at the interface between MgO and GdFeCo when the AHE probe current is applied. During the subsequent measurements on the RE-rich sample, we observe a moderate decrease in coercivity at low currents and the coercivity increases in a high current range. Such nonlinear dependence of coercivity on electric current can be explained by the competing interplay of the spin–orbit torque (SOT) and the Joule heating effects. On the other hand, for the TM-rich case, the SOT effect is observed over a widely applied current range. [ABSTRACT FROM AUTHOR]

Nickel ferrite ultrafine nanoparticles were synthesized by the sonochemical method. The sample was sintered at temperatures ranging from 1273 K to 1673 K for 3 h. XRD peaks of as-synthesized NiFe2O4, their Transmission Electron Microscopy (TEM), high resolution TEM, and selective area (electron) diffraction pattern demonstrate that the particles are in the completely crystalline state. The initial particle size of as-synthesized NiFe2O4 was found to be approximately <5 nm. Besides, NiFe2O4 samples were also synthesized by a conventional double sintering technique. The purpose was to compare the effect of sintering treatment on the microstructure quality of the NiFe2O4 prepared by these two techniques. Homogeneous coaxial grains did not form until 1573 K for conventionally prepared samples, while for the sonochemical method, homogeneous grains started to form even as low as 1373 K. Furthermore, other measurements were done only for the sintered samples prepared by the sonochemical method to evaluate the magnetic properties. An abrupt change in B–H loops was found with Ts for a maximum applied field of 1500 A/m. M–H loops with the maximum applied field of 1.6 × 103 KA/m and Mössbauer spectroscopy demonstrate that the samples are all at the ferrimagnetic stage. Curie temperatures Tc, determined from the temperature dependence of the initial permeability μ′, for the same samples almost remained unchanged, which confirms that the cation distribution is almost unchanged with the variation of Ts. A slight variation of cation distribution manifested in the variation of Tc with Ts conforms with the site occupancy of Fe3+ analyzed by Mössbauer spectroscopy. [ABSTRACT FROM AUTHOR]

We report the structural and magnetic behavior of single phase inverse Heusler alloys Cr2Co(1−x)CrxAl (x = 0, 0.2, and 0.4) by using x-ray diffraction (XRD), Raman spectroscopy, isothermal magnetization, and magnetic susceptibility measurements. Interestingly, the Rietveld refinement of XRD data with space group I 4 ¯ m 2 reveal a tetragonal distortion with a c/a ratio around 1.38 in these inverse Heusler structures. The bulk compositions have been confirmed by energy dispersive x-ray spectroscopy measurements. The active Raman mode F2g is observed at 320 cm−1, which confirms the X-type Heusler structure, as the A2 and B2 type structures are known to be not Raman active. The area of F2g mode decreases with an increase in the Cr concentration, which indicates that the origin of this mode is due to Co vibrations. The isothermal magnetization data confirm the magnetic moment to be close to zero (≤0.02 μB/f.u.) at ≈70 kOe and the negligible coercive field suggests the fully compensated ferrimagnetic nature of these samples. The susceptibility behavior indicates irreversibility between zero-field and field-cooled curves and complex magnetic interactions at low temperatures. [ABSTRACT FROM AUTHOR]

The Zero Field Cooled (ZFC) Exchange Bias (EB) effect in a single phase nanocrystalline Mg-ferrite thin film, deposited on an amorphous quartz substrate using pulsed laser ablation technique, is reported. The film showed a high ZFC EB shift (HE ∼ 190 Oe) at 5 K. The ZFC EB shift decreased with increasing temperature and disappeared at higher temperatures (T > 70 K). This Mg-ferrite thin film also showed the Conventional Exchange Bias (CEB) effect, but unlike many CEB systems, the film showed a decrease in coercivity (HC) under the Field Cooled measurements. The film also showed the training effect in ZFC measurements, which followed the frozen spin relaxation behavior. The observed exchange bias could be attributed to the pinning effect of the surface spins of frozen glassy states at the interface of large ferrimagnetic grains. [ABSTRACT FROM AUTHOR]

The current-driven domain wall dynamics along ferrimagnetic elements are here theoretically analyzed as a function of temperature by means of micromagnetic simulations and a one dimensional model. Contrarily to conventional effective approaches, our model takes into account the two coupled ferromagnetic sublattices forming the ferrimagnetic element. Although the model is suitable for elements with asymmetric exchange interaction and spin-orbit coupling effects due to adjacent heavy metal layers, we here focus our attention on the case of single-layer ferrimagnetic strips where domain walls adopt achiral Bloch configurations at rest. Such domain walls can be driven by either out-of-plane fields or spin transfer torques upon bulk current injection. Our results indicate that the domain wall velocity is optimized at the angular compensation temperature for both field-driven and current-driven cases. Our advanced models allow us to infer that the precession of the internal domain wall moments is suppressed at such compensation temperature, and they will be useful to interpret state-of-the art experiments on these elements. [ABSTRACT FROM AUTHOR]

We present a study of the transport properties of thermally generated spin currents in an insulating ferrimagnetic-antiferromagnetic-ferrimagnetic trilayer over a wide range of temperature. Spin currents generated by the spin Seebeck effect (SSE) in a yttrium iron garnet (YIG) YIG/NiO/YIG trilayer on a gadolinium gallium garnet (GGG) substrate were detected using the inverse spin Hall effect (ISHE) in Pt. By studying samples with different NiO thicknesses, the spin diffusion length of NiO was determined to be ∼3.8 nm at room temperature. Surprisingly, a large increase of the SSE signal was observed below 30 K, and the field dependence of the signal closely follows a Brillouin function for an S=7/2 spin. The increase of the SSE signal at low temperatures could thus be associated with the paramagnetic SSE from the GGG substrate. Besides, a broad peak in the SSE response was observed around 100 K. These observations are important in understanding the generation and transport properties of spin currents through magnetic insulators and the role of a paramagnetic substrate in spin current generation. [ABSTRACT FROM AUTHOR]

Magnetic properties in ferrimagnetic GdCo alloy films with bulk perpendicular magnetic anisotropy (PMA) are investigated as a function of annealing temperature (Tanneal) and annealing time for several capping layers. Magnetic properties in films capped by TaOx vary markedly with Tanneal; the saturation magnetization and coercivity vary progressively with increasing Tanneal up to 300°C, and above that temperature, PMA is lost abruptly. By comparing the annealing temperature dependence for Co-dominated and Gd-dominated compositions close to the magnetization compensation point, the data are readily explained by preferential oxidation of Gd during annealing. When films are capped by a Ta/Pt bilayer, the film properties are stable up Tanneal = 300 °C, indicating that oxidation at high temperatures is effectively blocked, but the abrupt loss of PMA for Tanneal > 300 °C is still observed. X-ray diffraction measurement reveals that the amorphous structure of the films remains the same after high-temperature annealing that is sufficient to remove PMA, indicating that crystallization from the amorphous phase is not responsible for the lack of PMA. Instead, our results suggest that high annealing temperatures may cause segregation of Co and Gd atoms in the films, which reduces anisotropic pair-pair correlations responsible for the observed bulk PMA in the as-grown state. [ABSTRACT FROM AUTHOR]

We investigate the temperature dependence and the thickness dependence of anomalous Hall effect (AHE) of TbFeCo ultra-thin films under high magnetic field. The sign change on temperature dependence of AHE in 20nm-thick TbFeCo film with rare-earth (RE) rich composition was observed. The AHE sign at low temperature is negative while it gradually becomes positive as the temperature increases. Moreover, the AHE sign for 5nm-thick TbFeCo film remains positive while that for 50nm-thick TbFeCo film remains negative at temperature in the range from 5 K to 400 K. The similar thickness dependence of AHE in TM-rich samples was also observed. From the mean-field approximation, the sign change temperature in AHE is related to the compensation temperature and the existence of interfacial region, which has the TM-rich composition and the weak anisotropy. Therefore, We clarified that the novel behavior of AHE sign changes in TbFeCo thin films with different thickness can be explained by the interfacial layer with weak anisotropy and two phase model. [ABSTRACT FROM AUTHOR]

Antiferromagnetic and ferrimagnetic microtubes decorated with nanowires have been obtained during thermal oxidation process, which was assisted by in situ electrical resistivity measurements. The synthesis route including heat treatment and electrical current along with growth mechanism are presented. This simple method and the ability to tune in the magnetic moment of the obtained microtubes going from a nonmagnetic-like to a large magnetization saturation open an avenue for interesting applications. In vitro experiments involving adherence, migration, and proliferation of fibroblasts cell culture on the surface of the microtubes indicated the absence of cytotoxicity for this material. We have also calculated both torque and driving magnetic force for these microtubes with nanowires and cells as a function of external magnetic field gradient which were found to be robust opening the possibility for magnetic bio micro-robot device fabrication and application in biotechnology. [ABSTRACT FROM AUTHOR]

All optical switching is an emerging recording technology by using femtosecond laser to realize ultrafast magnetization manipulation for super-high magnetic storage. TbCo films possess ferrimagnetic structure and large perpendicular anisotropy and thus have the potential to be used as a AOS material. In this paper, we simulate the ultrafast magnetization reversal of TbCo films under 100fs pulse laser with a general theoretical framework and the simulated results show that TbCo films can generate magnetization reversal at the timescale of several ps. Cosublattice completes demagnetization and subsequently triggers magnetize reversal within 1.0ps, whereas Tb- sublattice begins to magnetize reversal more than 4.0ps. Moreover, large laser power intensity easily induce the complete demagnetization and subsequent magnetization reversal regardless of the composition of TbCo films. [ABSTRACT FROM AUTHOR]

Amorphous Fe64Gd36 thin film square elements are investigated by imaging in the Fresnel mode of a transmission electron microscope (TEM). The equilibrium state without an applied field shows the well-known four-domain flux closure pattern with in-plane magnetization. However, the vortex is displaced from the center of the square element and the domain walls are curved. In a reference measurement of a thin Ni81Fe19 element, the vortex core is perfectly centered and the domain walls straight. When an increasing external field is applied in-plane, the vortex core can be moved. While this motion of the vortex core is linear in NiFe elements, in the ferrimagnetic FeGd squares the vortex core moves by sudden jumps. Micromagnetic simulations show that the asymmetry of the domain patterns as well as the vortex core pinning and depinning can be attributed to random anisotropy and a patchy microstructure in amorphous films. [ABSTRACT FROM AUTHOR]

We obtained the spin Seebeck effect enhancement in Y3Fe5O12 (YIG)/Pt system by inserting a very thin Ni80Fe20 at the interface of YIG/Pt. One of important parameters determining the spin Seebeck coefficient is the spin mixing conductance at the interface between magnetic oxide and nonmagnetic metal, and it was theoretically reported that the spin mixing conductance depends on the magnetic density at the interface. However, a ferrimagnetic oxide such as YIG has a small magnetic moment density. In this report, we fabricated YIG (1 mm)/Ni80Fe20 (t nm)/Pt (5 nm) and the spin Seebeck coefficient of t=0.6 nm becomes 2.1 times larger than that of t=0. It is considered owing to improvement of the magnetic moment density and the spin mixing conductance. [ABSTRACT FROM AUTHOR]

We investigated the electric-current-induced dynamics of bubble domains in a perpendicularly magnetized ferrimagnetic {Tb/Co}7 multilayer wire with a heavy-metal Pt cap layer. The {Tb/Cog}7 wire with the transition-metal-dominant and rare-earthdominant magnetizations was obtained by changing temperature. We found that the bubble domains moved to the electric current direction with growing in oblique angles when electric current pulses were applied. The oblique directions of the bubbledomain's growth in the {Tb/Co}7 wire with the transition-metal-dominant and rareearth- dominant magnetizations were opposite with each other. The micromagnetic simulations imply that these oblique growths are accounted by the spin injection from the Pt layer via the spin Hall effect. [ABSTRACT FROM AUTHOR]

Structural and electron-transport properties of thin films of the ferrimagnetic Heusler compound CoFeCrAl have been investigated to elucidate structure-property relationships. The alloy is, ideally, a spin-gapless semiconductor, but structural disorder destroys the spin-gapless character and drastically alters the transport behavior. Two types of CoFeCrAl films were grown by magnetron sputtering deposition at 973 K, namely polycrystalline films on Si substrates and epitaxial films on MgO (001) substrates. The resistivity decreases with increasing temperature, with relatively small temperature coefficients of -0.19 μΩcm/KμΩcm/K for the polycrystalline films and -0.12 μΩcm/KμΩcm/K for the epitaxial films. The residual resistivity of the polycrystalline films deposited on Si is higher than that of the epitaxial film deposited on MgO, indicating that the polycrystalline films behave as so-called dirty metals. [ABSTRACT FROM AUTHOR]

GdBaMn2O5.0 is a double-perovskite ferrimagnet consisting of pyramidal manganese layers. In this work, we study the in-plane and the c-axis thermal conductivities of GdBaMn2O5.0 single crystals at low temperatures down to 0.3 K and in high magnetic fields up to 14 T. The κc (T) curve shows a broad hump below the Néel temperature (TN = 144 K), which indicates the magnon heat transport along the c axis. Whereas, the κa (T) shows a kink at TN, caused by a magnon-phonon scattering effect. This anisotropic behavior is caused by the anisotropy of spin interactions along different directions. At very low temperatures, magnetic-field-induced changes of κa and κc, which is likely due to phonon scattering by free Gd3+ spins, is rather weak. This indicates that the spin coupling between Gd3+ and Mn2+/Mn3+ is rather strong at low temperatures. [ABSTRACT FROM AUTHOR]

In this work we investigated thin films of the ferrimagnetic insulators Y3Fe5O12 and NiFe2O4 capped with thin Pt layers in terms of the longitudinal spin Seebeck effect (LSSE). The electric response detected in the Pt layer under an out-of-plane temperature gradient can be interpreted as a pure spin current converted into a charge current via the inverse spin Hall effect. Typically, the transverse voltage is the quantity investigated in LSSE measurements (in the range of μV). Here, we present the directly detected DC current (in the range of nA) as an alternative quantity. Furthermore, we investigate the resistance of the Pt layer in the LSSE configuration. We found an influence of the test current on the resistance. The typical shape of the LSSE curve varies for increasing test currents. [ABSTRACT FROM AUTHOR]

The ferrimagnetic superlattice (SL) [MnGa/Co2FeAl]n exhibiting perpendicular magnetic anisotropy opened a new method for spintronics materials used in magnetic random access memory, because of the high anisotropy, small damping constant and tunable magnetization. In this work, we fabricated SLs with different MnGa composition and studied the MnGa composition dependence of the structure and magnetic properties of the SLs. Furthermore, we fabricated fully perpendicular magnetic tunnel junctions with SLs as both top and bottom electrodes. A clear tunnel magnetoresistance (TMR) effect with TMR ratio of 1.3% at room temperature was observed. [ABSTRACT FROM AUTHOR]

Composites of anisotropic diamagnetic multilayer Graphene (MLG) and ferrimagnetic CoFe2O4 (CFO) nanoparticles (NPs) were synthesized through a one-step sonication process in the presence of a surfactant. The samples were characterized at ambient using x-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy, magnetic force microscopy (MFM) and magnetometry (vibrating sample magnetometer). An induced ferromagnetism was observed in MLG with saturation magnetization MS = 18 emu/g(MLG). This induced ferromagnetism is attributed to ferrimagnetic CFO uniformly distributed on the surface of diamagnetic MLG. SEM images confirm uniform dense distribution of CFO nanoparticles on MLG. MFM images confirm the formation of larger magnetic domains in the composite sample of MLG/CFO. The measured coercivity HC = 3.6 Oe of MLG/CFO composite is much smaller than HC = 32.4 Oe of pristine CFO NPs; this difference in HC is attributed to the effect of change in surface anisotropy. [ABSTRACT FROM AUTHOR]