Compensation Of Magnetic Moments Research Articles

Magnetic properties of GdFeCo thin films tailored by sputtering conditions

The unique properties of ferrimagnets including easy detection of their dynamic and static states, strong resistance to external disturbances, and rapid dynamic characteristics, have made them attractive in the spintronics community. Our study focuses on the engineering of these magnetic properties of ferrimagnets, particularly employing a GdFeCo alloy, a prominent ferrimagnetic material, by utilizing magnetron sputtering. A series of GdFeCo films are fabricated by altering their thicknesses and working pressure during the sputtering process. Our experimental results reveal that these sputtering parameters significantly influence a Gd composition within the films, which in turn affects critical properties of ferrimagnets such as magnetic anisotropy, and magnetic moment compensation temperature. By precisely controlling these sputtering parameters, we successfully tailored the magnetic properties of the GdFeCo thin films with desired properties, offering new possibilities for the creation of sophisticated magnetic materials tailored to specific technological needs.

Neuromorphic Computing in Synthetic Antiferromagnets by Spin‐Orbit Torque Induced Magnetic‐Field‐Free Magnetization Switching

AbstractSynthetic antiferromagnet (SAF) with high thermal stability, ultra‐fast spin dynamics, and highly efficient spin‐orbit torque switching has great application potential in neuromorphic computing hardware. However, two challenges, the weakening of Hall signal in the remanent state and the need for a large auxiliary magnetic field for perpendicular magnetization switching, greatly limit the advantages of SAF in neuromorphic computing. In this work, both the enhanced anomalous Hall resistance and magnetic‐field‐free perpendicular magnetization switching are achieved by using oblique sputtering to fabricate the Pt/CoPt/Ru/CoTb SAF with strong interlayer exchange coupling and magnetic moment compensation. The fabricated SAF as synapse shows nearly linear, nonvolatile multistate plasticity, and as neuron exhibits a nonlinear sigmoid activation function, which are used to construct a fully connected neural network with a remarkable 97.0–98.1% recognition rate for the handwritten digits. Additionally, SAF serving as spike‐timing‐dependent plasticity synapse is used to construct an adaptive, unsupervised learning spiking neural network, and achieve an 87.0% accuracy in handwritten digit recognition. The findings exhibit the promise of SAFs as specialized hardware for high‐performance neuromorphic computing, offering high recognition rates and low power consumption.

Investigations of the variable magnetic moment automatic compensation efficiency improving possibility of three-phase electrical equipment currents

An analysis and review of known parametric systems for automatic compensation of electrical equipment the external magnetic field was carried out. It was found that the known parametric electrical equipment automatic compensation systems of the external magnetic field do not take into account the change in the order of alternating power phases when the level of the external magnetic field changes, which reduces the effectiveness of the three-phase electrical equipment magnetic field compensation by two to three times. The parametric system of three-phase electrical equipment sinusoidal currents magnetic moment automatic compensation with the phase alternation order sensor was improved, the distinguishing features of which are the preliminary determination of the phases alternation order in the power circuit of three-phase electrical equipment and the formation electromagnets compensators currents taking into account this order, which allows to increase the efficiency of three-phase electrical equipment currents magnetic moment compensation and use such a system in a three-phase distribution device containing a plurality of three-phase feeders. The system parameters bench adjustment method of the sinusoidal currents magnetic moment automatic compensation of three-phase electrical equipment with the phase alternation order sensor has been improved, which differs from known methods in that the phases order in the power circuit is determined in advance and the currents of the electromagnets compensators are formed taking into account this order and only then the power is supplied in turn, in each independent circuit of the electrical equipment power circuit an electromagnet compensator oriented along the selected axis is simultaneously turned on, the component of the total magnetic moment along the same axis is measured, and depending on its value, the magnitude and phase of the compensation currents signals are adjusted, then the sequence of alternating phases is changed and the rest of the operations are repeated. It is recommended to improve the non-sinusoidal currents magnetic moment system automatic compensation of three-phase electrical equipment with the phases alternating order sensor to ensure high efficiency of the magnetic moment compensation and the external magnetic field regardless of the power supply phases alternating order of three-phase electrical equipment.

Layer-resolved electronic behavior in a Kondo lattice system, CeAgAs2

We investigate the electronic structure of an antiferromagnetic Kondo lattice system CeAgAs2 employing hard x-ray photoemission spectroscopy. CeAgAs2, an orthorhombic variant of HfCuSi2 structure, exhibits antiferromagnetic ground state, Kondo like resistivity upturn and compensation of magnetic moments at low temperatures. The photoemission spectra obtained at different photon energies suggest termination of the cleaved surface at cis-trans-As layers. The depth-resolved data show significant surface-bulk differences in the As and Ce core level spectra. The As 2p bulk spectrum shows distinct two peaks corresponding to two different As layers. The peak at higher binding energy correspond to cis-trans-As layers and is weakly hybridized with the adjacent Ce layers. The As layers between Ce and Ag-layers possess close to trivalent configuration due to strong hybridization with the neighboring atoms and the corresponding feature appear at lower binding energy. Ce 3d core level spectra show multiple features reflecting strong Ce-As hybridization and strong correlation. Intense f 0 peak is observed in the surface spectrum while it is insignificant in the bulk. In addition, we observe a features at binding energy lower than the well-screened feature indicating the presence of additional interactions. This feature becomes more intense in the bulk spectra suggesting it to be a bulk property. Increase in temperature leads to a spectral weight transfer to higher binding energies in the core level spectra and a depletion of spectral intensity at the Fermi level as expected in a Kondo material. These results reveal interesting surface-bulk differences, complex interplay of intra- and inter-layer covalency, and electron correlation in the electronic structure of this novel Kondo lattice system.

Tuning the Structural and Magnetic Properties in Mixed Cation MnxCo2-xP2S6.

The metal thiophosphates (MTP), M2P2S6, are a versatile class of van der Waals materials, which are notable for the possibility of tuning their magnetic properties with the incorporation of different transition-metal cations. Further, they also offer opportunities to probe the independent and synergistic role of the magnetically active cation sublattice when coupled to P2Q6 polyhedra. Herein, we report the structural, magnetic, and electronic properties of the series of MTPs, MnxCo2-xP2S6 (x = 0.25, 0.5, 1, 1.5, 1.75) synthesized by the P2S5 flux method. Structural and elemental analysis indicates a homogeneous stoichiometry in the MnxCo2-xP2S6 compounds. We observe that a correlation is apparent between the intensities of specific Raman modes and Raman shifts with respect to the alloying ratio between Mn and Co. Magnetic susceptibility measurements indicate that the alloyed systems adopt an ordered antiferromagnetic (AFM) configuration with a dependence of the Néel temperature on the alloying ratio. A possible magnetic frustration behavior was observed for the composition MnCoP2S6 due to magnetic moment compensation as the alloying ratio between Mn and Co approaches parity. Interestingly, mixed oxidation states of the metal cation species are also observed in MnxCo2-xP2S6 along with a linear dependence of the work function on the alloying ratio of Mn and Co.

Reactive Sintering of Dysprosium-Iron Garnet via a Perovskite-Hematite Solid State Reaction and Physical Properties of the Material.

In this paper, we report on a successful synthesis of dysprosium iron garnet Dy3Fe5O12 (DyIG) by a reactive synthesis method involving dysprosium iron perovskite and hematite. Phase formation was traced using dilatometry, and XRD measurements attested to the formation of the desired structure. Samples with relative density close to 97% were fabricated. The samples were characterized using vibrating sample magnetometry, dielectric spectroscopy, and UV-Vis-NIR spectroscopy. Magnetic properties were probed in temperatures between 80 and 700 K with a maximum applied field of 1 kOe. The measurements revealed several effects: the compensation of magnetic moments at a certain temperature, the inversion of the magnetocaloric effect, and the ability to measure the Curie temperature of the material. Activation energy was determined from UV-Vis-NIR and dielectric spectroscopy measurements. Characteristic magnetic temperatures and activation energy values of the samples were similar to bulk DyIG obtained using other methods.

Neutron diffraction and ab initio studies on the fully compensated ferrimagnetic characteristics of Mn2V1−x Co x Ga Heusler alloys

Neutron diffraction and ab initio studies were carried out on Mn2V1−x Co x Ga (x = 0, 0.25, 0.5, 0.75, 1) Heusler alloys which exhibits high T C fully compensated ferrimagnetic characteristics for x = 0.5. A combined analysis of neutron diffraction and ab initio calculations revealed the crystal structure and magnetic configuration which could not be determined from the x-ray diffraction and magnetic measurements. As reported earlier, Rietveld refinement of neutron diffraction data confirmed L21 structure for Mn2VGa and X a structure for Mn2CoGa. The alloys with x = 0.25 and 0.5 possess L21 structure with Mn(C)–Co disorder. As the Co concentration reaches 0.75, a structural transition has been observed from disordered L21 to disordered X a. Detailed ab initio studies also confirmed this structural transition. The reason for the magnetic moment compensation in Mn2(V1−x Co x )Ga was identified to be different from that of the earlier reported fully compensated ferrimagnet (MnCo)VGa. With the help of neutron diffraction and ab initio studies, it is identified that the disordered L21 structure with antiparallel coupling between the ferromagnetically aligned magnetic moments of (Mn(A)–Mn(C)) and (V–Co) atom pairs enables the compensation in Mn2V1−x Co x Ga.

Magnetic characterization of a thin Co2MnSi/L10–MnGa synthetic antiferromagnetic bilayer prepared by MBE**Project supported by the National Program on Key Basic Research Project, China (Grant No. 2018YFB0407601), the Key Research Project of Frontier Science of the Chinese Academy of Sciences (Grant Nos. QYZDY-SSW-JSC015 and XDPB12), and the National Natural Science Foundation of China (Grant Nos. 11874349 and 11774339).

A synthetic antiferromagnet based on a thin antiferromagnetically coupled Co2MnSi/MnGa bilayer with Pt capping is proposed in this work. Square magnetic loops measured by anomalous Hall effect reveal that a well perpendicular magnetic anisotropy is obtained in this structure. A very large coercivity of 83 kOe (1 Oe = 79.5775 A⋅m−1) is observed near the magnetic moment compensation point of 270 K, indicating an antiferromagnetic behavior. Moreover, the anomalous Hall signal does not go to zero even at the magnetic compensation point, for which the difficulty in detecting the conventional antiferromagnets can be overcome. By changing the temperature, the polarity of the spin–orbit torque induced switching is changed around the bilayer compensation point. This kind of thin bilayer has potential applications in spin–orbit-related effects, spintronic devices, and racetrack memories.

Tuning interfacial Dzyaloshinskii-Moriya interactions in thin amorphous ferrimagnetic alloys

Skyrmions can be stabilized in magnetic systems with broken inversion symmetry and chiral interactions, such as Dzyaloshinskii-Moriya interactions (DMI). Further, compensation of magnetic moments in ferrimagnetic materials can significantly reduce magnetic dipolar interactions, which tend to favor large skyrmions. Tuning DMI is essential to control skyrmion properties, with symmetry breaking at interfaces offering the greatest flexibility. However, in contrast to the ferromagnet case, few studies have investigated interfacial DMI in ferrimagnets. Here we present a systematic study of DMI in ferrimagnetic CoGd films by Brillouin light scattering. We demonstrate the ability to control DMI by the CoGd cap layer composition, the stack symmetry and the ferrimagnetic layer thickness. The DMI thickness dependence confirms its interfacial nature. In addition, magnetic force microscopy reveals the ability to tune DMI in a range that stabilizes sub-100 nm skyrmions at room temperature in zero field. Our work opens new paths for controlling interfacial DMI in ferrimagnets to nucleate and manipulate skyrmions.

Manipulation of saturation magnetization and perpendicular magnetic anisotropy in epitaxial CoxMn4−xN films with ferrimagnetic compensation

Spintronics devices utilizing a magnetic domain-wall motion have attracted increasing attention, and ferrimagnetic materials with almost-compensated magnetic moments are highly required to realize the fast magnetic domain-wall motion. Here, we report a key function for this purpose in the antiperovskite $\mathrm{C}{\mathrm{o}}_{x}\mathrm{M}{\mathrm{n}}_{4\ensuremath{-}x}\mathrm{N}$ film. We have grown $\mathrm{C}{\mathrm{o}}_{x}\mathrm{M}{\mathrm{n}}_{4\ensuremath{-}x}\mathrm{N}$ films with various Co/Mn ratios on $\mathrm{SrTi}{\mathrm{O}}_{3}(001)$ by molecular-beam epitaxy. High-quality growth is confirmed and a perpendicular magnetization emerges at $x=0$, 0.2, 0.5, and 0.8, whereas it turns into in plane for $x\ensuremath{\ge}1.1$. The saturation magnetization ${M}_{S}$ decreases as $x$ increases and reaches a minimum value of $15\phantom{\rule{0.16em}{0ex}}\mathrm{emu}/\mathrm{c}{\mathrm{m}}^{3}$ at $x=0.8$. Then, it increases with $x$ when $0.8\ensuremath{\le}x\ensuremath{\le}3.6$ and saturates. These results indicate that ${M}_{S}$ and magnetic anisotropy of $\mathrm{C}{\mathrm{o}}_{x}\mathrm{M}{\mathrm{n}}_{4\ensuremath{-}x}\mathrm{N}$ films can be manipulated by the Co composition. X-ray absorption spectroscopy and magnetic circular dichroism measurements revealed that Co atoms tend to occupy the I site in the antiperovskite lattice and reasonably explains the origin of minimum ${M}_{S}$ near $x=0.8$, where a compensation of magnetic moments occurs among different atomic sites. We consider that the nearly compensated ferrimagnetic $\mathrm{C}{\mathrm{o}}_{0.8}\mathrm{M}{\mathrm{n}}_{3.2}\mathrm{N}$ is suitable for application to current-induced domain-wall motion devices.

Ultrafast spin dynamics and spintronics for ferrimagnets close to the spin compensation point (Review)

The possibilities of applying magnets with full or partial magnetic moment compensation in various spin groups to improve the performance of magnetic electronic devices using spin current (spintronics) are discussed. The effects of an exchange enhancement of the spin dynamics in antiferromagnets are well known. Over the past few years, antiferromagnetic spintronics has turned into an independent, rapidly developing field of applied physics of magnetism. This article provides for a detailed analysis of the possibility of using another class of magnetic materials, such as ferrimagnets close to the spin compensation point, in which the indicated acceleration effects are also detected. A comparative analysis of these two classes of magnets is conducted. The nonlinear spin dynamics of ferrimagnets are examined using a nonlinear sigma-model for the antiferromagnetic vector, describing the difference in spin densities of various spin groups. The simple conclusion derived based on this model is presented, and its real parameters for popular ferrimagnets, amorphous alloys of iron, and rare earth elements, are discussed. The different nonlinear effects of spin dynamics, ranging from homogeneous spin vibrations in small particles to the dynamics of solitons, domain walls, ferrimagnetic skyrmions, and vortices, are analyzed. The possibility of exciting such dynamic modes using spin torque, and their application in ultrafast spintronics is considered.

Magnetooptic Properties of Bismuth-Substituted Ferrite–Garnet Films in Strong Pulsed Magnetic Fields

Abstract—A technique of measuring the rotation of the light polarization plane in pulsed magnetic fields with strength up to 40 T with a sensitivity of 0.1° is proposed. The Faraday effect has been studied in films of diluted ferrites—garnets (Lu,Bi)3(Fe,Ga,Al)5O12 in the temperature range from room temperature to 78 K, including the vicinity of the magnetic moment compensation temperature. The transition to the noncollinear phase in the magnetic phase diagram is shown to occur at a magnetic field strength higher than 30 T at room temperature, and the threshold transition field tends to zero when approaching the magnetic moment compensation temperature.

Near total magnetic moment compensation with high Curie temperature in Mn2V0.5Co0.5Z (Z = Ga,Al) Heusler alloys

Mn2V1−xCoxZ (Z = Ga,Al and x = 0, 0.25, 0.5, 0.75, 1) Heusler alloys have been synthesized to investigate the effect of Co substitution at the V site on the magnetic moment and Curie temperature of half-metallic ferrimagnets Mn2VGa and Mn2VAl. Near total magnetic moment compensation was achieved with high Curie temperature for x = 0.5 composition. The Co substituted alloys show a non linear decrease in lattice parameter without altering the crystal structure of the parent alloys. The end members Mn2VGa and Mn2CoGa have the saturation magnetization of 1.80 µB/f.u. and 2.05 µB/f.u. respectively whereas for the Mn2V0.5Co0.5Ga alloy, a near total magnetic moment compensation (0.10 µB/f.u.) was observed due to the ferrimagnetic coupling of Mn with parallelly aligned V and Co. The Co substituted Mn2VAl has also shown a similar trend with compensated magnetic moment value of 0.06 µB/f.u. for x = 0.5. The Curie temperatures of the alloys including the x = 0.5 composition are well above the room temperature (more than 650 K) which is in sharp contrast to the earlier reported values of 171 K for the (MnCo)VGa and 105 K for the (MnCo)VAl (substitution at the Mn site). The observed TC values are highest among the Mn2V based fully compensated ferrimagnets. The magnetic moment compensation without significant reduction in TC indicates that the V site substitution of Co does not weaken the magnetic interaction in Mn2VZ (Z = Ga,Al) alloys which is contrary to the earlier experimental reports on Mn site substitution.

Магнитооптические свойства висмутзамещенных пленок ферритов-гранатов в сильных импульсных магнитных полях

Abstract —A technique of measuring the rotation of the light polarization plane in pulsed magnetic fields with strength up to 40 T with a sensitivity of 0.1° is proposed. The Faraday effect has been studied in films of diluted ferrites—garnets (Lu,Bi)_3(Fe,Ga,Al)_5O_12 in the temperature range from room temperature to 78 K, including the vicinity of the magnetic moment compensation temperature. The transition to the noncollinear phase in the magnetic phase diagram is shown to occur at a magnetic field strength higher than 30 T at room temperature, and the threshold transition field tends to zero when approaching the magnetic moment compensation temperature.

Design and Synthesis of an Artificial Perpendicular Hard Ferrimagnet with High Thermal and Magnetic Field Stabilities

It is of great fundamental and practical interest to develop effective means of modulating the magnetic hystereses of magnetic materials and their heterostructures. A notable example is the exchange bias (EB) effect between an antiferromagnet or ferrimagnet and a ferromagnet, which has been widely employed to manipulate magnetic anisotropy in spintronic devices and artificial magnets. Here, we report the design, synthesis and characterization of a synthetic perpendicularly-magnetized ferrimagnet based on [Mn2.9Ga/Co2MnSi]n superlattices, which attains thermal stability above 400 K and a coercive field up to 45 kOe through a mechanism of magnetic compensation. The structure is incorporated into a prototype Heusler alloy and MgO barrier based magnetic tunnel junction, which demonstrates high dynamic range linear field responses and an unusual in-plane EB effect. With increasing temperature, the coercive field reaches beyond 70 kOe at 400 K in this device due to the increasing degree of magnetic moment compensation in the superlattice. The results demonstrate that the compensation mechanism can be utilized to achieve simultaneous thermal robustness and high coercivity in realistic spintronic devices.

Structure, magnetism, and magnetic compensation behavior of Co50-xMn25Ga25+x and Co50-xMn25+xGa25 Heusler alloys

The structure, magnetism, magnetic compensation behavior, exchange interaction, and electronic structures of Co50-xMn25Ga25+x and Co50-xMn25+xGa25 (x = 0–25) alloys have been systematically investigated by both experiments and first-principles calculations. We found that all the samples exhibited body centered cubic structures with high degree of atomic ordering. With increasing Ga content, the composition dependence of lattice parameter shows a kink point at the middle composition in Co50-xMn25Ga25+x alloys, which can be attributed to the enhanced covalent hybridization between the main-group Ga and the transition-metal atoms. Moreover, a complicated magnetic competition has been revealed in Co50-xMn25Ga25+x alloys, which causes the Curie temperature dramatically decrease and results in a magnetic moment compensation behavior. In Co50-xMn25+xGa25 alloys, however, with increasing Mn content, an additional ferrimagnetic configuration is established in the native ferromagnetic matrix, which causes the molecular moment monotonously decrease and the exchange interaction enhance gradually. The electronic structure calculations indicate that the Co50-xMn25+xGa25 alloys are likely to be in a coexistence state of the itinerant and localized magnetism. Our study will be helpful to understand the nature of magnetic ordering as well as to tune magnetic compensation and electronic properties of Heusler alloys.

Unusual lattice constant changes and tunable magnetic moment compensation in Mn50−xCo25Ga25+x alloys

We report on unusual lattice parameter changes and tunable magnetic moment compensation in Mn50−xCo25Ga25+x (x = 0-25) Heusler alloys by substituting Ga for Mn. The observed lattice parameter first increases with increasing Ga content x, showing a maximum at x = 12.5, and then abnormally decreases due to the enhanced covalence effect between transition-metal and main-group atoms. Moreover, a tunable magnetic moment compensation was also observed due to the diversification in role of the main magnetic contributor when the structure varies from Hg2CuTi-type Mn2CoGa to Cu2MnAl-type CoMnGa2. These results provide an alternative way to simultaneously tune both the structural and magnetic properties of Heusler alloys, which is particularly important for developing flexible spintronics devices.

Magnetic tunnel junctions with compensated magnetic moment by directly exchange-coupled NiFe∕CoGd∕NiFe trilayers

The compensation of magnetic moments plays a major role in magnetic tunnel junction electrodes and is usually established by artificial trilayer ferrimagnets such as CoFe∕Ru∕CoFe. An alternative route is described here: trilayers consisting of ferromagnetic rare earth and transition metals show an antiparallel exchange coupling of the individual layers. In magnetic tunnel junctions consisting of IrMn exchange biased NiFe∕CoGd∕NiFe trilayers the total magnetic moment can thus be compensated by an appropriate choice of the individual layer thicknesses. Consequently, an enhancement of the exchange bias field and a strong reduction of the Neél coupling can be found in parallel. The compensation point can be shifted on the temperature scale by the CoGd composition, even to values above room temperature.

Structural and magnetic properties of Laves compounds Dy1−xPrx(Fe0.35Co0.55B0.1)2 (⩽x⩽1)

Dy 1 − x Pr x ( Fe 0.35 Co 0.55 B 0.1 ) 2 (0⩽x⩽1) Laves compounds with a cubic MgCu2-type structure were synthesized by arc melting and subsequent annealing. The lattice parameter of the Laves compounds linearly increases, while the Curie temperature TC decreases with increasing Pr content. The saturation magnetization Ms at 5K or 295K for the Dy1−xPrx(Fe0.35Co0.55B0.1)2 alloys decreases to reach a minimum, then increases with increasing Pr content. The composition for magnetic moment compensation is about x=0.55 at 295K and x=0.65 at 5K, respectively. The magnetostriction λ‖ or λ⊥ at room temperature was investigated either parallel or perpendicular to the applied field using a standard strain gauge technique.

Ferrimagnetic properties of Co/(Gd–Co) multilayers

Co/(Gd–Co) multilayers have been prepared by rf-sputtering and investigated by means of Transverse Magnetooptic Kerr Effect (TMOKE), SQUID and VSM magnetometry. The composition of amorphous Gd 0.36 Co 0.64 layers was chosen so that their saturation magnetization was dominated by Gd moments in all the temperature range. Co and Gd–Co layers formed a macroscopic ferrimagnetically coupled system displaying a compensation temperature. Complete magnetic moment compensation was found at such point. An inversion of TMOKE hysteresis loops and a divergent behaviour of coercivity were also observed. By changing the layers thickness it has been possible to control the magnetic characteristics of the Co/(Gd–Co) structures, in particular the compensation takes place at different temperatures.