Tb Atoms Research Articles

Enhancement of thermal stability of Nd–Fe–B sintered magnets with tuned Tb-diffused microstructures via temperature control

We investigate the magnetic properties and thermal stability of Tb-diffused Nd–Fe–B magnets prepared at various grain-boundary diffusion temperatures and additional heat-treatment temperatures. These heat-treatment processes improved the coercivity of Tb-diffused Nd–Fe–B magnets than that of the base magnets. The diffusion temperature was found to play a key role in controlling the magnetic thermal stability; temperature variations induced precise changes in the decoupled Tb-diffused microstructures in the magnets. The magnet fabricated at a high diffusion temperature showed the best coercivity at room temperature but poor thermal stability. This was due to the formation of Tb-rich (Tb, Nd)2Fe14B phases with high magnetocrystalline anisotropy produced inside the grains and less core–shell structures during diffusion at a higher temperature. The best thermal stability was observed for the magnet prepared at a lower diffusion temperature. This magnet had more well-formed core–shell structures than the remaining magnets. By analyzing its microstructure, using electron microscopy and a micromagnetic equation, it was found that a decoupled microstructure with diffused Tb atoms was mainly responsible for the better thermal magnetic stability. Results obtained herein suggest that an optimized diffusion temperature can provide a magnet with good thermal stability.

Magnetic properties and microstructure evolution of in-situ Tb-Cu diffusion treated hot-deformed Nd-Fe-B magnets

In this work, Tb70Cu30 alloy is employed as the addition for enhancing the hard magnetic properties of hot-deformed Nd-Fe-B magnets through in-situ diffusion. The magnets with and without Tb-Cu addition were prepared by hot pressing at 700 °C followed by hot deformation at different temperatures using melt spun Nd-Fe-B based powder as the raw materials. Tb and Cu elements were found to diffuse into the magnet after preparation. By adding 2 wt% Tb70Cu30, the coercivity and thermal stability of hot-deformed magnet were significantly improved due to the formation of local high-anisotropy (Nd,Tb)2Fe14B phase and the reduction in grain size. The intrinsic coercivity Hcj increased from 1281 kA/m to 1681 kA/m and the absolute value of temperature coefficient of coercivity |β| decreased from 0.479%/°C to 0.431%/°C for the magnets hot-deformed at 750 °C. It was confirmed that the diffused Tb atom prefers to substituting Nd in Nd2Fe14B type main phase rather than entering into RE-rich phase, and Cu distributes mainly at the grain boundaries. The reduction in crystal orientation was observed for diffused magnets, which is related to the increased rare earth-rich phase, resulting in the decreased remanence. The evolutions of the grain orientation, microstructure and magnetic properties of the magnets prepared at different hot-deformation temperatures were discussed as well.

Modulation of spin effect in electronic and vibrational properties of terbium dihydride (TbH2): An ab-initio study

The interaction of hydrogen with terbium was correlated and the structural and electronic structure properties for the cubic rare earth terbium dihydride (TbH2) using density functional theory (DFT) have been studied. The electronic band structure and density of states (DOS) for spin-up, spin-down and non-spin cases were studied and furthermore influence of higher pressure was also investigated. The charge contribution shows that TbH2 has metallic characteristic with a mixed covalent and ionic bonding. The Fermi surfaces show hole type structure and provide a space where hydrogen can be absorbed and filled easily. The Löwdin population analysis show that the decrease in charge density of Tb atom which explain absorption of H atom by Tb. The charge density of TbH2 also show decrease in differential charge density which verify the Löwdin population analysis. Furthermore, we have also analysed phonon dispersion curve at ambient and higher pressure and changes were studied. The TbH2 can be a good alternative to develop a hydrogen storage device as mass ratio percentage is around 1.27%.

Tuning magnetostriction of Fe–Ga alloys via stress engineering

Stress has a strong impact on the magnetization and magnetostriction of magnetic materials due to the magneto-elastic coupling. It offers a clue to understand the 2–5 times enhancement on the magnetostriction of Fe–Ga alloys with rare-earth elements doping. In this article, the stress states of melt-quenched and melt-spun (Fe0.83Ga0.17)100-xTbx (x = 0–0.47) alloys were measured by high energy X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) technique. The macroscopic residual and microscopic stress of different Tb doped alloys were deduced from the shift and broadening of diffraction peaks and the deviation of the identified 1st Fe–Fe and 2nd Ga–Ga bond length. Rietveld refinement confirmed that the dissolved Tb atoms can replace the Fe/Ga site while small-angle neutron scattering (SANS) showed the presence of Tb-rich nanoscale precipitates. The effect of external stress loading and Tb doping on magnetization and magnetostriction of the modified Fe–Ga alloys was compared and discussed. We propose that the magnetization and magnetostriction of Fe–Ga alloys can be controlled through stress engineering by manipulating the magnetic domain structure through chemical doping or mechanical loading.

Magnetocaloric effect of the Gd3-xTbxCo system

Gd3-xTbxCo compounds with x = 0, 0.25, 0.5, 1, 1.5, 2, 2.5 and 3 were investigated using structural and magnetic methods. The lattice parameters, and the location of 4c and 8d Wyckoff sites occupied by Gd, Tb, and Co atoms, in an Fe3C–orthorhombic type of structure, were refined by the Rietveld method. The magnetic ordering temperature changes linearly with Tb content. The magnetocaloric effect (MCE) in Tb3Co at 77 K and a magnetic field of 7 T is equal to −28.8 J/kgK. An inverse MCE observed in GdTb2Co reaches its maximum value of 6.8 J/kgK at 47 K and a magnetic field of 6 T.

Continious series of solid solutions Tb2Ni17-xCox, 0 ≤ x ≤ 17. Structural and electrochemical characteristics of alloys

Synthesis, study of the phase, structural and electrochemical characteristics of the alloys from homogeneity range of the continious series of solid solutions Tb 2 Ni 17- x Co x (0 ≤ x ≤ 17) was carried out in the prototype of NiMH battery for the purpose of search of new materials for modern electrical energy sources. The samples for investigation were synthesized by arc melting of pure components under an argon atmosphere with further annealing at 600 oC for one month in evacuated silica ampules. X-ray powder diffraction, scanning electron microscopy, X-ray fluorescent and energy dispersive X-ray spectroscopy were used to examine the alloys before and after electrochemical studies. The process of electrochemical hydrogenation of the samples was carried out in two-electrode “Swagelok-cell” prototype of NiMH battery. Studied alloys were used as anode materials (during discharging of the batteries). A mixture of Ni(OH) 2 and graphite served as cathode material (during discharging of the batteries). The anode and cathode materials were soaked by 6 M solution of KOH as electrolite and separated by pressed cellulose to avoid contacts between them. During charging we obtained the hydride of inclusion on the basis of Tb 2 Ni 17- x Co x phases. The process of hydrogenation is characterized by one stage, namely the inclusion of H-atoms into vacant tetrahedral and octahedral voids. At the small hydrogen concentration its atoms occupy the octahedral voids (6 h ) formed by two Tb atoms and four (Ni, Co) atoms. As electrode materials, the studied phases are relatively stable in the electrolyte solution. Increasing of the cobalt content improves the electrode capacity, but decreases the corrosion stability of the electrodes to the action of the electrolyte that is confirmed by the decreasing of crystallinity, passivation of the surfaces and changing of quantitative compositions of the samples. The amount of mobile hydrogen under the same conditions (during discharge) is the following: 1.53 H/f.u. for Tb 2 Ni 17 , 1.83 H/f.u. for Tb 2 Ni 12 . 2 Co 4 . 8 and 2.08 H/f.u. for Tb 2 Ni 6 . 5 Co 10 . 5 . The specific capacity does not exceed 60 mA∙h/g. The electrochemical processes in all cases led to changing of the surface morphology, reducing of the grains size. Significant amorphization was observed for electrodes with higher content of Co. Keywords : intermetallic compound, continious series of solid solutions, electrochemical hydrogenation, nickel metal hydride batteries.

The Impact of the Composition Effect on Ferromagnetic Properties of Tb2Co2Ga

The ferromagnetic properties of Tb2Co2Ga, crystallizing into an orthorhombic W2CoB2-type structure, were investigated by preparing 11 polycrystalline samples with different starting atomic compositions. We found that Tb2Co2Ga possesses a homogeneity range in the ternary phase diagram. The Curie temperature TC is sensitive to the atomic composition and ranges rather widely, i.e., from 75 to 145 K. For the samples with a TC above 90 K, the nearest Tb–Tb and the Tb–Co distances would be important factors deciding TC, considering the RKKY interaction through the hybridization between Tb and Co atoms. An anisotropic change of two kinds of Co–Tb–Co angles in the octahedron formed by two Tb and four Co atoms occurs in the samples with a TC lower than 90 K. Such a change of octahedral parameters seems to be related to a difference of shapes in the ac magnetization anomaly at TC between the samples in the lowest TC (~ 75 K) group and those in the other groups.

Structural stability and evolution of terbium‐doped silicon clusters and influence of 4f → 5d electronic transition mechanism on magnetism and appearance of photoelectron spectroscopy for TbSin0/− (n = 6‐18) clusters

AbstractThe global minimal structures of terbium‐doped Si clusters and their anions TbSi n0/− (n = 6‐18) are confirmed by employing the ABCluster unbiased global search technique combined with a B2PLYP double‐hybrid density functional and comparing consistency of simulated and experimental photoelectron spectroscopy (PES). The results demonstrated that structural evolution patterns for neutral clusters prefer Tb‐substitutional to Tb‐encapsulated configuration starting from n = 16. While for the corresponding anionic clusters, the growth pattern adopts Tb‐linked structures to encapsulated motif. The Natural Population Analysis revealed that the 4f electrons of Tb atom in TbSi n0/− (n = 6‐18) clusters participate in bonding. The way to participate in bonding is one 4f electron transition to 5d orbital ([Xe]6s24f9 → [Xe]6s24f85d1), which significantly affects the cluster's magnetism and appearance of PES. The total magnetic moments of neutral TbSi n and the corresponding anions maintain at 7 μB and 6 μB, respectively, which are larger than that of an isolated Tb atom. The HOMO‐LUMO energy gap, relative stability, and chemical bonding analysis demonstrated that superatomic TbSi16− cluster is a magic cluster with fine thermodynamic and moderate chemical stability.

MM-Fe-B based gap magnet with excellent energy density

TbHx nanoparticles were applied to prepare sintered MM-Fe-B magnet by using grain boundary diffusion technique. Under optimal processing conditions, the coercivity and maximum energy product substantially increase by 383% and 151%, reaching to 6.81 kOe and 20.18 MGOe, respectively. Further investigation indicates that the interchange between Tb atoms and Ce atoms leads to a core/shell structure with (MM,Tb)2Fe14B phase in the surface region of MM2Fe14B matrix grains in the magnet. The modified structure successfully restrains the magnetic domain reversal process, resulting in remarkable enhancement of coercivity and maximum energy product of the magnet.

Composition effect in ferromagnetic properties of Tb3Co3Ga

The magnetic properties of Tb3Co3Ga, crystallizing into the orthorhombic W3CoB3-type structure, have been investigated by focusing on a composition effect. Tb3Co3Ga has been characterized as a ferromagnet by measuring the dc and ac magnetic susceptibilities and the magnetization curve. We have found that the Curie temperature determined by the ac susceptibility is highly sensitive to the atomic composition, and ranges from 90 K to 117 K. The crystal structure parameters slightly change with the Ga concentration. The lattice parameter a correlates with the coercive field; a shrinkage of a leading to an enhanced crystalline anisotropy increases the coercive field. There are two inequivalent crystallographic sites Tb1 and Tb2 for Tb atoms. The narrowing of the Tb1-Tb2-Tb1 angle would contribute to the enhanced Curie temperature, which can be qualitatively explained by considering the 4f charge distribution of Tb3+ ion.

Regulating element distribution to improve magnetic properties of sintered Nd–Fe–B/Tb–Fe–B composite magnets**Project supported by the National Natural Science Foundation of China (Grant Nos. 51861030 and 51571126) and the National Key Research and Development Program of China (Grant No. 2016YFB0700900).

Nd content was varied in B6 (x = 0, 0.5, 1, and 1.5) to optimize the magnetic properties of sintered Nd–Fe–B/Tb–Fe–B composite magnets, which were prepared by mixing 9 g of Nd–Fe–B with 1 g of Tb17Fe75B8 powder. In conventional magnets, by reducing Nd content, the coercivity of 10.4 kOe in Nd13.2Fe80.8B6 decreases to 7.2 kOe in Nd12.2Fe81.8B6; meanwhile, in Nd–Fe–B/Tb–Fe–B magnets the coercivity does not decrease when reducing Nd content. In the intergranular phase, the Tb content increases owing to the reducing Nd content of the Nd–Fe–B alloy in the sintered composite magnets. Therefore, the excess Tb in Tb17Fe75B8 enters the intergranular phase, and more Tb atoms can substitute for Nd at the grain boundary of the Nd–Fe–B phase, leading to a more significant increase in coercivity. The remanence increases with reducing Nd content, and the energy product of 39.1 MGOe with a high coercivity of 21.0 kOe is obtained in Nd12.2Fe81.8B6/Tb17Fe75B8 magnets. These investigations show that magnetic properties can be further improved by regulating the element distribution in sintered composite magnets.

Effect of Tb-Fe diffusion on magnetic properties and thermal stability of hot-deformed magnets

Hot-deformed Nd-Fe-B magnets co-doped with and without Tb-Fe addition are prepared to study the effect of Tb-Fe particles on the magnetic properties and thermal stability. With the addition of 2 wt. % Tb-Fe particles, the coercivity increases by 28.7%, while the remanence decreases by only 3.6%. It is observed that Tb atoms are diffused from the Tb-Fe particles to neighboring Nd-Fe-B melt-spun ribbons, in which Nd atoms in 2:14:1 grains are partially substituted by Tb atoms. The formation of local high-anisotropy (Nd, Tb)2Fe14B regions promotes the locally magnetically hardening, suppressing the nucleation of reversed magnetic domains at the low-anisotropy surface magnetic “defects”. This can be employed to explain the coercivity enhancement of diffusion-processed hot-deformed magnets. In addition, the thermal stability of the magnet is improved due to the higher Curie temperature of (Nd, Tb)2Fe14B grain.

Spin-orbit torque-induced switching in ferrimagnetic alloys: Experiments and modeling

We investigate spin-orbit torque (SOT)-induced switching in rare-earth-transition metal ferrimagnetic alloys using W/CoTb bilayers. The switching current is found to vary continuously with the alloy concentration, and no reduction in the switching current is observed at the magnetic compensation point despite a very large SOT efficiency. A model based on coupled Landau-Lifschitz-Gilbert (LLG) equations shows that the switching current density scales with the effective perpendicular anisotropy which does not exhibit strong reduction at the magnetic compensation, explaining the behavior of the switching current density. This model also suggests that conventional SOT effective field measurements do not allow one to conclude whether the spins are transferred to one sublattice or just simply to the net magnetization. The effective spin Hall angle measurement shows an enhancement of the spin Hall angle with the Tb concentration which suggests an additional SOT contribution from the rare earth Tb atoms.

Femtosecond Laser-Induced Magnetization Reversal Domain of Co-Sublattice in TbCo Film

All-optical switching (AOS) is an emerging recording technology by using femtosecond laser to manipulate the ultrafast magnetization reversal for future super high density magnetic storage. TbCo films possess a ferrimagnetic structure and large perpendicular anisotropy and, thus, become a potential material for AOS. In this paper, we simulate the ultrafast magnetization reversal domain of Co-sublattice in TbCo films under 100 fs pulse laser with a general theoretical framework, and our simulation results show that TbCo films irradiated with a higher power fluence laser have a larger reversal domain of Co-sublattice due to the higher peak temperature and the further critical isotherm of electrons. Moreover, high Co content can help Co-sublattice form a large reversal domain, but is unable to obtain the highly uniform reversal domain perhaps attributed to the insufficient anti-ferromagnetic interaction between Tb atoms and Co atoms.

Comparison on the Coercivity Enhancement of Hot-Deformed Nd2Fe14B-Type Magnets by Doping R70Cu30(R = Nd, Dy, and Tb) Alloy Powders

Coercivity enhancement effect of the anisotropic hot-deformed NdFeB magnets made from NdFeB MQU-F powders doped with 2 wt% low-melting R70Cu30 (R = Nd, Dy, and Tb) powders was explored. Post-annealing treatment at 600 °C and 700 °C was employed to modify the microstructures and therefore improve the magnetic properties of the hot-deformed magnets. Doping R70Cu30 alloy powders into the hot-deformed NdFeB magnets is effective in enhancing the coercivity from 15.1 kOe to 16.3–23.6 kOe, depending on the rare-earth elements adopted. The coercivity increment $\Delta _{i}\text{H}_{c}$ is 1.2 and 4.4 kOe for the magnets doped with Nd70Cu30 and Dy70Cu30 alloy powders, respectively. Most interestingly, Tb70Cu30-doped magnet followed with 700 °C post-annealing exhibits the highest coercivity i H c of 23.6 kOe and the highest coercivity increment of 8.5 kOe. TEM analysis shows that annealing treatment not only modifies the grain boundary of the platelet 2:14:1 phase but also promotes more Tb atoms entering into 2:14:1 crystal. As a result, the coercivity of the magnets is effectively enhanced.

Triboluminescence and crystal structure of centrosymmetric complex Tb(AcAc)3Phen

The atomic structure of crystals of the complex Tb(AcAc)3Phen (AA –acetylacetonate-anion, Phen – 1,10 - phenanthroline) characterized by an intensive luminescence and triboluminescence has been determined by means of the X-ray structural analysis method. The crystal structure is represented by individual С27Н29N2O6Tb complexes linked through van der Waals interactions with clearly expressed cleavage planes. The structural aspects of the suggested model of formation of the triboluminescent properties have been considered and the role of the cleavage planes has been discussed. The notions of destruction zone and destruction zone width were introduced for the crystal under mechanical impact. This zone boundaries and width are naturally determined by surfaces spreading through central Tb atoms of molecular complexes, on which the ionization of charged acetylacetonate ions occurs as a result of the mechanical impact. In the case of the studied complex, the width of such destruction zone is equal to 6.414Å.

The Density Functional Study of Structural, Electronic, Magnetic and Thermodynamic Properties of XFeSi (X = Gd, Tb, La) and GdRuSi Compounds

The structural, electronic, magnetic, and thermodynamic properties of XFeSi (X = Gd, Tb, La) and GdRuSi compounds are investigated using density functional theory by the WIEN2k code. Using the first-principle procedure, the Hubbard parameter of Gd and Tb 4f electrons and La 5d electrons of XFeSi (X = Gd, Tb, La) and GdRuSi compounds is calculated. The structural and electronic and magnetic properties of these compounds within GGA and GGA + U approaches in the presence of spin-orbit coupling are calculated and compared. The calculated results indicate that the ferromagnetic phase is the most stable phase of XFeSi (X = Gd, Tb) and GdRuSi compounds and the nonmagnetic phase is the stable phase of LaFeSi. The magnetic moment of GdFeSi, GdRuSi, and TbFeSi compounds is due to Gd and Tb atoms. The calculated electronic band structures of these compounds show that these compounds have metallic behavior. Furthermore, the thermodynamic properties of these compounds using the quasi-harmonic Debye model as a function of temperature and pressure within GGA and GGA + U approaches are investigated.

Electronic magnetic structure of intermetallic compounds RNi2Mn studied by XMCD

The x-ray absorption near edge structure (XANES) and the x-ray magnetic circular dichroism (XMCD) measurements in the hard X-ray range at the Ni and Mn K edges and Tb, Dy L2, 3 edges were carried out in TbNi2Mn and DyNi2Mn in magnetic field up to 6T at 10K. XMCD on the Dy and Tb L-edges reaches 3.2%. The spin and orbital d-projected density of states on Tb and Dy atoms were obtained from the XMCD spectra. The Ni and Mn K-edges absorptions are practically identical in both compounds, as well as the dichroism spectra. The magnitude of dichroism is less than 0.5% and its length of about 50eV. Scattering of outgoing p-wave on magnetic atoms environment is the main source of the K-edge dichroism. Element-specific magnetic hysteresis-loops measurements on TbNi2Mn and DyNi2Mn were performed by X-ray magnetic circular dichroism.

Substitution disorder and photoluminescent property of a new rare-earth borate: K3TbB6O12

Abstract A new rare-earth borate K3TbB6O12 has been prepared using the high temperature molten salt method and was structurally determined by single crystal X-ray diffraction analyses. The structure features a three-dimensional (3D) framework which is composed of isolated B5O10, KO6, KO8 and TbO6 groups. An atom site in the 32 screw axis is shared by K and Tb atoms with the molar ratio of 1:1. The self-activated photoluminescence (PL) property of K3TbB6O12 was studied. Under the excitation of 378 nm, the emission spectrum exhibits an intense green emission centered at 543–548 nm with the chromaticity coordinates (0.342, 0.590), which can be assigned to the 5D4→7F5 transition of Tb3+. The excitation spectra cover a wide range from 330 to 385 nm, which suggests that the K3TbB6O12 phosphors can be effectively excited by a near-UV light source. One may expect that compound K3TbB6O12 can be used as a green phosphor pumped by near-UV LED chips.

Di- and tetranuclear heterometallic 3d–4f cobalt(II)–lanthanide(III) complexes derived from a hexadentate bisoxime: Syntheses, structures and magnetic properties

Five heterometallic Co(II)–Ln(III) complexes, a discrete heterodinuclear complex [CoLLa(Py)(NO3)3(CH3OH)] (1) (Py=pyridine), a heterotetranuclear dimer [Co2L2La2(4,4′-bipy)(NO3)6(CH3OH)2] (2) (4,4′-bipy=4,4′-bipyridine) and three discrete heterodinuclear complexes [CoLLn(OAc)(NO3)2(CH3OH)] (Ln=Gd (3), Tb (4), Dy (5)), were synthesized with a hexadentate bisoxime ligand 1,2-bis(3-methoxysalicylideneaminooxy)ethane (H2L), and characterized by single crystal X-ray diffraction. The complexes 1, 3, 4 and 5 are discrete heterodinuclear structures, but the assembly of two dinuclear units [CoLLa(NO3)3(CH3OH)] and one 4,4′-bipyridine results in a discrete heterotetranuclear dimer 2. The Co(II) and La(III) atoms in the complexes 1 and 2 are penta- and decacoordinated, while the Co(II) and Ln(III) (Ln=Gd, Tb and Dy) atoms in the complexes 3, 4 and 5 are hexa- and nonacoordinated, respectively. Magnetic measurements were performed on the complexes 3, 4 and 5, where an intramolecular ferromagnetic interaction is found in the complex 3.