Showing papers on "Ferrimagnetism published in 2019"
TL;DR: It is shown that epitaxial rare-earth iron garnet films with perpendicular magnetic anisotropy exhibit homochiral Néel domain walls that can be propelled faster than 800 m s−1 by spin current from an adjacent platinum layer.
Abstract: Magnetic oxides exhibit rich fundamental physics1–4 and technologically desirable properties for spin-based memory, logic and signal transmission5–7. Recently, spin–orbit-induced spin transport phenomena have been realized in insulating magnetic oxides by using proximate heavy metal layers such as platinum8–10. In their metallic ferromagnet counterparts, such interfaces also give rise to a Dzyaloshinskii–Moriya interaction11–13 that can stabilize homochiral domain walls and skyrmions with efficient current-driven dynamics. However, chiral magnetism in centrosymmetric oxides has not yet been observed. Here we discover chiral magnetism that allows for pure spin-current-driven domain wall motion in the most ubiquitous class of magnetic oxides, ferrimagnetic iron garnets. We show that epitaxial rare-earth iron garnet films with perpendicular magnetic anisotropy exhibit homochiral Neel domain walls that can be propelled faster than 800 m s−1 by spin current from an adjacent platinum layer. We find that, despite the relatively small interfacial Dzyaloshinskii–Moriya interaction, very high velocities can be attained due to the antiferromagnetic spin dynamics associated with ferrimagnetic order. Spin currents from an adjacent Pt layer can drive homochiral Neel domain walls in centrosymmetric rare-earth iron garnet films at more than 800 m s–1, taking advantage of the antiferromagnetic spin dynamics of the ferrimagnetic oxide.
139 citations
TL;DR: In this paper, the structural, magnetic and electrical properties of two-component composites with controllable magnetic properties have been investigated in terms of microstructure analysis, including grain size, porosity and density.
Abstract: This paper described to the ceramics (inorganic) two-component composites with controllable magnetic and electrical properties. Ceramic composite samples were produced via solid state reaction method (standard ceramic technique) from initial magnetic (BaFe11.9Al0.1O19 or BF) and ferroelectric (BaTiO3 or BT) phases. BT and BF initial compounds were mixed in stoichiometric ratios (BF)1-x - (BT)x (x = 0, 0.25, 0.5, 0.75 and 1) and sintered. Initial compounds BaFe11.9Al0.1O19 (x = 0) and BaTiO3 (x = 1) were also produced via standard ceramic technique. The constituent materials were chosen considering their perspective ferrimagnetic and ferroelectric properties, respectively for BF and BT. Moreover, Ba-hexaferrites are reported to exhibit ferroelectricity at room temperature as well, and the combination of two ferroelectric phases is of interest. Systematic investigations of the structural, magnetic and electrical properties versus chemical composition (x) were performed. As structural properties we have defined the features of crystal structure (a and c lattice parameters, volume of unit cell) and peculiarities of microstructure (density, porosity, average grain size). The ferrimagnetic phase transition temperature is almost independent of the content of BT, which is determined by the exchange interactions Fe3+-O2--Fe3+in the magnetic phase. However, the coercivity of composite samples is lower which is due to the contribution of the microstructure dependent shape-anisotropy to the total magnetic anisotropy energy. The permittivity vs. temperature behavior confirmed the existence of two ferroelectric phase transitions corresponding to structural phase transitions in BT (at about 400 K) and BF (at about 700 K). It was observed that the electrical properties of composite samples, including the temperatures of the phase transitions, critically depended on concentration x which affects the composite microstructure. This behavior was discussed in terms of microstructure analysis (grain size, porosity and density).
110 citations
TL;DR: In this paper, the structural and magnetic properties of coordination polymers containing azide and carboxylate as simultaneous bridges between paramagnetic metal ions have been investigated, sometimes in collaboration with other short bridges of different types, leading to discrete, one-, two, and even three-dimensional magnetic motifs.
100 citations
TL;DR: Eu3+ doping was shown to have significant influence on the structure and magnetic attributes of the proposed CNMEuF NPs and values of various magnetic parameters of proposed compositions were reduced with the increase in Eu 3+ dopant contents.
100 citations
TL;DR: The van der Waals epitaxy of nonlayered magnets introduces a new route for realizing magnetism in 2D limit and provides more application potential in the 2D spintronics.
Abstract: Two-dimensional (2D) magnetic materials provide an ideal platform for the application in spintronic devices due to their unique spin states in nanometer scale. However, recent research on the exfoliated monolayer magnetic materials suffers from the instability in ambient atmosphere, which needs extraordinary protection. Hence the controllable synthesis of 2D magnetic materials with good quality and stability should be addressed. Here we report for the first time the van der Waals (vdW) epitaxial growth of one-unit-cell-thick air-stable ferrimagnet Cr2S3 semiconductor via a facile chemical vapor deposition method. Single crystal Cr2S3 with the domain size reaching to 200 μm is achieved. Most importantly, we observe the as grown Cr2S3 with a Neel temperature (TN) of up to 120 K and a maximum saturation magnetic momentum of up to 65 μemu. As the temperature decreases, the samples show a transition from soft magnet to hard magnet with the highest coercivity of 1000 Oe. The one-unit-cell-thick Cr2S3 devices sh...
98 citations
TL;DR: In this article, the effect of Nb3+ substitution on the magnetic and structural properties of CoFe2O4 nanoparticles (NPs) synthesized by hydrothermal approach was investigated.
88 citations
TL;DR: The observed mode coupling is theoretically explained as arising from the broken rotational symmetry due to a weak magnetocrystalline anisotropy, which is exchange enhanced around the ferrimagnetic compensation point.
Abstract: We experimentally study the spin dynamics in a gadolinium iron garnet single crystal using broadband ferromagnetic resonance. Close to the ferrimagnetic compensation temperature, we observe ultrastrong coupling of clockwise and counterclockwise magnon modes. The magnon-magnon coupling strength reaches almost 40% of the mode frequency and can be tuned by varying the direction of the external magnetic field. We theoretically explain the observed mode coupling as arising from the broken rotational symmetry due to a weak magnetocrystalline anisotropy. The effect of this anisotropy is exchange enhanced around the ferrimagnetic compensation point.
86 citations
TL;DR: SrTmxFe12−xO4 (0.10) hexaferrites (HFs) are produced successfully using a sol-gel approach in this paper, where structural, optical, and magnetic properties are investigated.
Abstract: SrTmxFe12−xO4 (0.00 ≤ x ≤ 0.10) hexaferrites (HFs) are produced successfully using a sol–gel approach. The structural, optical, and magnetic properties are investigated. The hexagonal phase is confirmed for all the products. The magnetization is measured with respect to the applied magnetic field, M(H). The magnetic parameters including saturation magnetization Ms, remanence Mr, squareness ratio (SQR = Mr/Ms), coercivity Hc, and magnetic moment n B are deduced at room (300 K; RT) and low (10 K) temperatures. It is shown that the ferrimagnetic nature and Tm3+ substitutions lead to decreases in the magnetization and coercivity magnitudes. The results on magnetic properties are investigated extensively with respect to the structural and microstructural properties. The SQR values indicate the formation of a single magnetic domain for the x = 0.0 sample and a multi-magnetic domain structure for the Tm3+-substituted Sr HFs (x ≥ 0.02). The obtained Hc values suggest that the produced HFs are promising candidates for potential magnetic recording applications.
85 citations
TL;DR: In this article, the authors report a long spin coherence length and associated bulk-like torque characteristics in an antiferromagnetically coupled ferrimagnetic multilayer, and they find that a transverse spin current can pass through >10-nm-thick ferromagnetic Co/Tb multilayers, whereas it is entirely absorbed by a 1-nmthick Co/Ni multiilayer.
Abstract: Spintronics relies on magnetization switching through current-induced spin torques. However, because spin transfer torque for ferromagnets is a surface torque, a large switching current is required for a thick, thermally stable ferromagnetic cell, and this remains a fundamental obstacle for high-density non-volatile applications with ferromagnets. Here, we report a long spin coherence length and associated bulk-like torque characteristics in an antiferromagnetically coupled ferrimagnetic multilayer. We find that a transverse spin current can pass through >10-nm-thick ferrimagnetic Co/Tb multilayers, whereas it is entirely absorbed by a 1-nm-thick ferromagnetic Co/Ni multilayer. We also find that the switching efficiency of Co/Tb multilayers partially reflects a bulk-like torque characteristic, as it increases with ferrimagnet thickness up to 8 nm and then decreases, in clear contrast to the 1/thickness dependence of ferromagnetic Co/Ni multilayers. Our results on antiferromagnetically coupled systems will invigorate research towards the development of energy-efficient spintronics.
84 citations
TL;DR: In this article, the effect of dysprosium (Dy) ions on the structural, microstructural and magnetic properties of nickel nanospinelferrite, NiFe2O4.
82 citations
TL;DR: In this paper, a co-substitution effect on morphological, structural, optical and magnetic properties of NiFe2O4 NPs was analyzed via FT-IR, XRD, TEM, SEM, DRS and VSM techniques.
TL;DR: Magnetic, optic and microstructural properties of ultrasonically synthesized CoEuxFe2-xO4 (x ≤ 0.1) nanoferrites (NFs) have been examined in this study and a decreasing trend in the Ms, Mr and nB values was noted with Eu3+ substitutions.
TL;DR: In this paper, the impact of vanadium substitution on the structural, magnetic, and optical properties of NiFe2−xVxO4 (x ≤ 0.3) nanoparticles (NPs) produced by the cost-effective sol-gel route was investigated.
Abstract: The current study investigates the impact of vanadium substitution on the structural, magnetic, and optical properties of NiFe2−xVxO4 (x ≤ 0.3) nanoparticles (NPs) produced by the cost-effective sol-gel route. The as-prepared spinel ceramic powders were examined by X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (DRS), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). The functional groups, spinel phase, and crystal structure were confirmed by XRD and FT-IR, respectively. The crystallites size decreased from 45.24 to 36.56 nm as the doping process increases. The plots of Tauc were drawn to determine optical band gap magnitudes of 1.291, 1.302, and 1.312 eV for x = 0.0, 0.2, and 0.3, respectively. The estimated saturation magnetization is maximum for pristine NiFe2O4 NPs and decreases to minimum for NiFe1.7V0.3O4 NPs. The σ-H hysteresis loops have finite coercivity (between 125 and 169 Oe) and retentivity (between 9.36 and 14.04 emu/g) values. The calculated σr/σs ratios are lower than 0.500, assigning the uniaxial anisotropy for NiFe2−xVxO4. The effective anisotropy constants (Keff) are in the range of 0.824 × 105 and 1.303 × 105 Erg/g. The magnetocrystalline anisotropy field (Ha) values are around 5.0 kOe. The characteristics of hysteresis (σ-H) curves and the order of magnetic data reveal the soft ferrimagnetic feature of as-prepared nanoparticle samples. From Mossbauer analysis, the variations in hyperfine magnetic field, quadrupole splitting, line width, and isomer shift have been evaluated. The distribution of cations showed that the octahedral B sites are occupied by all the ions of V3+. Mossbauer spectra are composed of four Zeeman sextets and one doublet.
TL;DR: In this paper, a high-entropy oxide nanocrystalline powder with chemical and microstructure homogeneity has been successfully synthesized, for the first time by a modified solution combustion synthesis method at synthesis temperature above 623
TL;DR: In this article, the authors present an experimental and theoretical investigation of all-optical switching by single femtosecond laser pulses, and they identify the switching mechanism as a front of reversed Co magnetization that nucleates near the Co/Gd interface and propagates through the Co layer driven by exchange scattering.
Abstract: We present an experimental and theoretical investigation of all-optical switching by single femtosecond laser pulses. Our experimental results demonstrate that, unlike rare-earth transition-metal ferrimagnetic alloys, $\mathrm{Pt}/\mathrm{Co}/{[\mathrm{Ni}/\mathrm{Co}]}_{N}/\mathrm{Gd}$ can be switched in the absence of a magnetization compensation temperature, indicative for strikingly different switching conditions. In order to understand the underlying mechanism, we model the laser-induced magnetization dynamics in Co/Gd bilayers and GdCo alloys on an equal footing, using an extension of the microscopic three-temperature model to multiple magnetic sublattices and including exchange scattering. In agreement with our experimental observations, the model shows that Co/Gd bilayers can be switched for a thickness of the Co layer far away from compensating the total Co and Gd magnetic moment. We identify the switching mechanism in Co/Gd bilayers as a front of reversed Co magnetization that nucleates near the Co/Gd interface and propagates through the Co layer driven by exchange scattering.
TL;DR: In this paper, the spectral properties of single-phase hexaferrite have been studied through XRD, SEM, EDX (Energy-dispersive X-ray), TEM (Transmission electron microscopy), DR% (UV-Visible diffuse reflectance spectrophotometer), FT-IR (Fourier transform infrared spectrophotsometer).
Abstract: Hexaferrite (HFs) of Sr1−xZrxFe12O19 (0.00 ≤ x ≤ 0.10) have been produced through Citrate Sol-gel approach. The characteristic of compositions is studied through XRD (X-ray powder diffractometer), SEM (Scanning electron microscopy), EDX (Energy-dispersive X-ray), TEM (Transmission electron microscopy), DR% (UV–Visible diffuse reflectance spectrophotometer), FT-IR (Fourier transform infrared spectrophotometer). The single-phase Sr hexaferrite was confirmed for each product by XRD. The crystallites size of the products was calculated as 22–40 nm range which makes this material as an appropriate candidate for high density recording media. The optical band gap tends to decrease when increasing the Zr content. The analyses of magnetization versus applied magnetic field, M(H), were performed at room (300 K; RT) and low (10 K) temperatures. The various magnetic parameters including coercivity Hc, squareness ratio (SQR = Mr/Ms), remanence Mr, saturation magnetization Ms and magnetic moment nB were deduced and described in detail. At both considered temperatures, the M(H) results showed ferrimagnetic nature. It is showed that the Zr substitutions significantly affect the magnetizations data. A significant decrease in the Ms, Mr, and nB was observed with Zr substitution.
TL;DR: The design of 2D organometallic frameworks with typical antiaromatic rings such as pentalene, which show Curie temperatures well above room temperature from classic Heisenberg model Monte Carlo simulations, confirms this proposal.
Abstract: Two-dimensional (2D) magnetic semiconductors with room-temperature ferromagnetism are very desirable. Despite the great progress made recently, the Curie temperature is still very low (∼45 K), originating from the weak ferromagnetic superexchange interaction. Here, based on first-principles calculations, we propose a general route to achieve 2D magnetic semiconductors with enhanced Curie temperature in organometallic frameworks by incorporating antiaromatic rings as organic linkers. Antiaromatic rings usually possess low-energy multiple spin states, which can be easily induced by adjacent magnetic moments of transition metals and subsequently coupled with them through the strong d–p direct exchange interaction, producing high-temperature ferrimagnetic ordering. The design of 2D organometallic frameworks with typical antiaromatic rings such as pentalene, which show Curie temperatures well above room temperature from classic Heisenberg model Monte Carlo simulations, confirms our proposal.
TL;DR: In this article, the effects of annealing process on the soft magnetic properties were investigated, and it was shown that the Fe3O4 insulating layer was coated on the surface of the iron powders, which effectively reduced the magnetic dilution and decreased the core loss of the composites.
TL;DR: In this paper, the magnetic field controlled electrical polarization is studied in hydrothermally synthesized multiferroic 0.25BaTiO3-0.75CoFe2O4 (BTO-CFO) nanocomposite.
TL;DR: The results demonstrate the high potential of the vortex beams with OAM as a new spectroscopic probe of magnetism in matter as well as the conventional dichroism for circularly polarized light.
Abstract: Circularly polarized light with spin angular momentum is one of the most valuable probes of magnetism. We demonstrate that light beams with orbital angular momentum (OAM), or vortex beams, can also couple to magnetism exhibiting dichroisms in a magnetized medium. Resonant optical absorption in a ferrimagnetic crystal depends strongly on both the handedness of the vortex and the direction of the beam propagation with respect to the sample magnetization. This effect exceeds the conventional dichroism for circularly polarized light. Our results demonstrate the high potential of the vortex beams with OAM as a new spectroscopic probe of magnetism in matter.
TL;DR: In this article, the formation of single phase cubic spinel with crystallite sizes in the range of 30-42nm was characterized by X-ray diffraction (XRD), Mossbauer Spectroscopy (MS), and Vibrating Sample Magnetometer (VSM).
TL;DR: This study provides important insights into the functional design of NiCo2 O4 for developing spinel-based spintronic applications and reveals the intricate interplay between the spin-dependent impurity scattering, band intrinsic Berry phase effect, and electron correlation.
Abstract: The inverse spinel ferrimagnetic NiCo2 O4 presents a unique model system for studying the competing effects of crystalline fields, magnetic exchange, and various types of chemical and lattice disorder on the electronic and magnetic states. Here, magnetotransport anomalies in high-quality epitaxial NiCo2 O4 thin films resulting from the complex energy landscape are reported. A strong out-of-plane magnetic anisotropy, linear magnetoresistance, and robust anomalous Hall effect above 300 K are observed in 5-30 unit cell NiCo2 O4 films. The anomalous Hall resistance exhibits a nonmonotonic temperature dependence that peaks around room temperature, and reverses its sign at low temperature in films thinner than 20 unit cells. The scaling relation between the anomalous Hall conductivity and longitudinal conductivity reveals the intricate interplay between the spin-dependent impurity scattering, band intrinsic Berry phase effect, and electron correlation. This study provides important insights into the functional design of NiCo2 O4 for developing spinel-based spintronic applications.
TL;DR: The authors show reversal of non-volatile magnetization by electric field as well as the polarization switching by magnetic field in a single-component material, close to room temperature.
Abstract: Mutual control of the electricity and magnetism in terms of magnetic (H) and electric (E) fields, the magnetoelectric (ME) effect, offers versatile low power consumption alternatives to current data storage, logic gate, and spintronic devices. Despite its importance, E-field control over magnetization (M) with significant magnitude was observed only at low temperatures. Here we have successfully stabilized a simultaneously ferrimagnetic and ferroelectric phase in a Y-type hexaferrite single crystal up to 450 K, and demonstrated the reversal of large non-volatile M by E field close to room temperature. Manipulation of the magnetic domains by E field is directly visualized at room temperature by using magnetic force microscopy. The present achievement provides an important step towards the application of ME multiferroics. Mutual control of the electric polarization and magnetization promises for low power consumption spintronic devices but remains challenging. Here the authors show reversal of non-volatile magnetization by electric field as well as the polarization switching by magnetic field in a single-component material, close to room temperature.
TL;DR: Using the Monte Carlo simulation, the magnetic and thermodynamic properties of a ferrimagnetic mixed-spin (1, 3/2, 2) ternary metal nanoisland with core-shell structure in external magnetic field have been researched detailedly.
Abstract: Using the Monte Carlo simulation, the magnetic and thermodynamic properties of a ferrimagnetic mixed-spin (1, 3/2, 2) ternary metal nanoisland with core–shell structure in external magnetic field have been researched detailedly. The effects of crystal-field, exchange coupling and temperature on magnetization, susceptibility, blocking temperature and internal energy as well as hysteresis loops behavior of the system have been exhibited. Some interesting phenomena such as multiple saturation magnetizations and rich hysteresis loops behaviors have been found. The results can be comparable with some theoretical and experimental researches.
TL;DR: By studying the spin-orbit torque induced switching in the Heusler alloy Mn2 Ru1- x Ga, it is found that efficient current-induced magnetic switching can be realized in a nearly compensated sample with strong perpendicular anisotropy and large film thickness.
Abstract: Ferrimagnetic materials combine the advantages of the low magnetic moment of an antiferromagnet and the ease of realizing magnetic reading of a ferromagnet. Recently, it was demonstrated that compensated ferrimagnetic half metals can be realized in Heusler alloys, where high spin polarization, zero magnetic moment, and low magnetic damping can be achieved at the same time. In this work, by studying the spin-orbit torque induced switching in the Heusler alloy Mn2 Ru1- x Ga, it is found that efficient current-induced magnetic switching can be realized in a nearly compensated sample with strong perpendicular anisotropy and large film thickness. This work demonstrates the possibility of employing compensated Heusler alloys for fast, energy-efficient spintronic devices.
TL;DR: In this article, a model representing the double perovskite Sr2CrIrO6 in order to simulate and to predict its magnetic properties is presented, which is done using the Monte Carlo method under the Metropolis algorithm.
Abstract: The double perovskite Sr2CrIrO6 has very important characteristics for spintronic applications. It is a ferrimagnetic material distinguished by its high Curie temperature. This manuscript presents a model representing the double perovskite Sr2CrIrO6 in order to simulate and to predict its magnetic properties. This compound contains only two magnetic atoms, namely: Cr (S = 3/2) and Ir ( σ = 2 ). Our simulations are done using the Monte Carlo method under the Metropolis algorithm. We present the behavior of the magnetization and the susceptibilities as a function of the temperature. Also, we discuss the effect of the physical parameters such as the coupling exchange interactions, the crystal field and the external magnetic field. To complete this study, we have presented the ground state by exposing the different phase diagrams in different planes of the physical parameters. Moreover, we establish the magnetic hysteresis loops of this compound.
TL;DR: Time-resolved soft x-ray magnetic circular dichroism measurements of the ferrimagnetic GdFeCo alloy are reported on allowing us to record the dynamics of elemental spin and orbital moments at the Fe and Gd sites during femtosecond laser-induced demagnetization.
Abstract: One of the key processes setting the speed of the ultrafast magnetization phenomena is the angular momentum transfer from and into the spin system. However, the way the angular momentum flows during ultrafast demagnetization and magnetization switching phenomena remains elusive so far. We report on time-resolved soft x-ray magnetic circular dichroism measurements of the ferrimagnetic GdFeCo alloy allowing us to record the dynamics of elemental spin and orbital moments at the Fe and Gd sites during femtosecond laser-induced demagnetization. We observe a complete transfer of spin and orbital angular momentum to the lattice during the first hundreds of femtoseconds of the demagnetization process.
TL;DR: In this paper, the Monte Carlo simulation has been used to study the magnetic and thermodynamic properties of a cylindrical ferrimagnetic Ising nanowire system with core/shell structure.
Abstract: The Monte Carlo simulation has been used to study the magnetic and thermodynamic properties of a cylindrical ferrimagnetic Ising nanowire system with core/shell structure Phase diagrams are attained with diverse single-ion anisotropies and exchange couplings It is discovered plentiful phase transitions in the nanowire system, for example, the compensation behaviors, the second-order and first-order phase transitions as well as the tricritical point phenomena We have discussed the significant effects of single-ion anisotropies, exchange couplings and temperature on the magnetization, the susceptibility, the internal energy and the specific heat for the cylindrical core/shell nanowire system In addition, we have also found the existence of two types of triple hysteresis loops behaviors for certain physical parameters It is interesting to achieve satisfying results to compare our results obtained with other theoretical and experimental studies
TL;DR: In this paper, the authors demonstrated the reversal of large nonvolatile M by E field close to room temperature by using magnetic force microscopy, which provides an important step towards the application of bulk ME multiferroics.
Abstract: Mutual control of the electricity and magnetism in terms of magnetic (H) and electric (E) fields, the magnetoelectric (ME) effect, offers versatile low power-consumption alternatives to current data storage, logic gate, and spintronic devices. Despite its importance, E-field control over magnetization (M) with significant magnitude was observed only at low temperatures. Here we have successfully stabilized a simultaneously ferrimagnetic and ferroelectric phase in a Y-type hexaferrite single crystal up to T=450K and demonstrated the reversal of large non-volatile M by E field close to room temperature. Manipulation of the magnetic domains by E field is directly visualized at room temperature by using magnetic force microscopy. The present achievement provides an important step towards the application of bulk ME multiferroics.
TL;DR: A new oxide NaCu3Fe2Os2O12 is synthesized using high pressure and temperature conditions and the Rietveld structural analysis shows that the compound possesses both A- and B-site ordered quadruple perovskite structure in Pn3̅ symmetry.
Abstract: A new oxide NaCu3Fe2Os2O12 is synthesized using high pressure and temperature conditions. The Rietveld structural analysis shows that the compound possesses both A- and B-site ordered quadruple perovskite structure in Pn3 symmetry. The valence states of transition metals are confirmed to be Cu2+/Fe3+/Os5.5+. The three transition metals all take part in magnetic interactions and generate strong Cu2+(↑)Fe3+(↑)Os5.5+(↓) ferrimagnetic superexchange interactions with a high Curie temperature about 380 K. Electrical transport measurements suggest its half-metallic properties. The first-principles theoretical calculations demonstrate that the compound has a spin-down conducting band and a spin-up insulating band with a wide energy gap.