Tb Magnetic Moments Research Articles

(Invited) Magnetism of Tb3N@C80 Endofullerenes

Tb3N@C80 was one of the first trimetallic endofullerenes to be studied in view of its magnetization where the microscopic picture of 3 Tb magnetic moments non-collinearly aligned by the ligand field of the central nitrogen ion was proposed [1]. The triangular geometry results in a net molecular magnetization of two Tb3+ ions or 18 μB. Today, this is confirmed with 23 possible pseudospin arrangements of the 3 Tb magnetic moments, resulting in a frustrated magnetic ground state with fluctuating pseudospins [2]. This picture does not include coherent tunneling of the magnetization, which is predicted within an 8-dimensional Hamiltonian and can be tested with low temperature magnetization measurements. Experimentally, we find a low temperature hysteresis that identifies Tb3N@C80 as a single molecule magnet. More surprisingly, we observe room temperature ferromagnetism in cubic single crystallites of the molecules using SQUID magnetometry. Since the magnetic interaction between adjacent carbon cages is expected to be dipolar it is neglected in the explanation of magnetic order above 3 K [3] and it is challenging to explain this finding with endofullerene magnetism. We present a series of analytical chamistry results of samples with and without room temperature ferromagnetism.[1] M. Wolf et al. Angew. Chem. Int. Ed. 44, 3306 (2005).[2] R. Westerström et al. Phys. Rev. B, 89, 060406(R) (2014).[3] A. Kostanyan et al. Phys. Rev. B, 101, 134429 (2020).

Crystal and magnetic structures of R2Ni2In compounds (R = Tb and Ho).

Crystal and magnetic structures of R2Ni2In (R = Tb and Ho) have been studied using powder neutron diffraction at low temperatures. The compounds crystallize as orthorhombic crystal structures of the Mn2AlB2 type. At low temperatures, the magnetic moments localized solely on the rare earth atoms form antiferromagnetic structures. The Tb magnetic moments, equal to 8.8 (4) μB and parallel to the c axis, form a collinear magnetic structure described by the propagation vector k = [½ , ½ , ½]. This magnetic structure is stable up to the Néel temperature TN = 40 K. For Ho2Ni2In a complex, temperature-dependent magnetic structure is detected. In the temperature range 6.1-8.6 K, an incommensurate sinusoidal magnetic structure, described by the propagation vector k1 = [0.24, 1, 0.52] is observed, while in the temperature interval 2.2-2.5 K a square-modulated magnetic structure, related to k2 = [0.17,{{5} \over {6}},{{1} \over {2}}] (the component along the a axis slightly differs from the commensurate value) and its third harmonics 3k2 = [0.50,{{5} \over {2}},{{3} \over {2}}] is found. At 3.1-3.7 K as well as below 2 K, a coexistence of both detected magnetic structures is observed. The Ho magnetic moments remain parallel to the c axis in both the sine- and square-modulated magnetic structures. The low-temperature heat capacity data confirm a first-order transition near 3 K.

Canting Angle Behavior of Magnetic Moments in Y‐Substituted Tb2BaNiO5 and Its Relevance for Magnetoelectric Coupling

The Haldane‐spin chain compound, Tb2BaNiO5, has been known to be an exotic multiferroic system, exhibiting antiferromagnetic anomalies at T N1 = 63 K and T N2 = 25 K, with ferroelectricity appearing below T N2 only. Previous reports in addition have established that, interestingly, Tb ions play a direct and decisive role to lead to multiferroic properties with a critical canting angle of magnetic moments, unlike other well‐known multiferroics. Herein, the results of temperature‐dependent neutron powder diffraction studies on Tb2–x Y x BaNiO5 are reported, to get an insight into the critical canting angle for multiferroic behavior. While multiferroic transition temperature decreases linearly with Y concentration, there is an abrupt drop of relative canting angle (of Tb and Ni magnetic moments) with respect to that in the parent compound for an initial substitution of x = 0.5 in the multiferroic region, without any notable change thereafter. Therefore, it is inferred that this critical canting angle is made up of two components—cooperative (long‐range) and local (short‐range) contributions.

Effect of pseudo-Tsai cluster incorporation on the magnetic structures of R−Au−Si (R=Tb,Ho) quasicrystal approximants

In cluster-based quasicrystals, tetrahedra located in conventional Tsai clusters may be replaced by single rare-earth $(R)$ ions at the cluster centers (pseudo-Tsai clusters). In this study, we investigate the effect of the pseudo-Tsai cluster incorporation on the magnetic structures of two approximants, the Tsai-type Tb-Au-Si [denoted TAS(0)] and Ho-Au-Si [denoted HAS(52)] with partial replacement of conventional Tsai clusters by pseudo-Tsai clusters, up to 52%. The mixture of Tsai and pseudo-Tsai clusters can be considered a different source of randomness/disorder other than the conventional chemical mix sites (Au/Si). The effect of the latter has been previously discussed regarding the origin/cause of spin-glass-like ordering and Anderson localization of electronic states in quasicrystals and approximant crystals. Single crystal neutron diffraction experiments at 2 K were performed and bulk physical properties (magnetization and specific heat) were investigated. In addition, earlier collected powder neutron diffraction data of TAS(14) with 14% replacement was reanalyzed in light of the results on TAS(0) and HAS(52). We find that the arrangement of ordered magnetic spins in the icosahedral shells of these phases is similar, while the cluster-center $R$ magnetic states are different. In the case of TAS(14), the cluster-center Tb magnetic moments seem to affect the arrangement of surrounding icosahedral magnetic moments, and the magnetic structure of the icosahedral shell deviates from that of TAS(0). In the case of HAS(52), however, the icosahedral $R$ magnetic moments are less affected by the cluster-center $R$, while the averaged cluster-center $R$ magnetic moments are significantly diminished. We discuss these results considering the magnetic ordering effect on the bulk physical properties.

Revisiting the antiferromagnetic structure of Tb14Ag51: the importance of distinguishing alternative symmetries for a multidimensional order parameter

The antiferromagnetic structure of Tb14Ag51 with the propagation vector [1/3, 1/3, 0] and the parent space group P6/m is revisited using both magnetic symmetry and irreducible representation arguments. A new magnetic structure under the hexagonal Shubnikov magnetic space group P 6′ which fits much better the experimental data is found. This new solution was obtained by constraining the spin arrangement to one of the three possible magnetic space groups of maximal symmetry that can be realized by a magnetic ordering transforming according to the four-dimensional physically irreducible representation that is known to be relevant in this magnetic phase. The refined model, parameterized under P 6′, implicitly includes the presence of a third harmonic with the propagation vector at the gamma point [0, 0, 0], which has an important weight in the final result. The structure consists of 13 symmetry-independent Tb magnetic moments with the same size of 8.48 (2) μB, propagating cycloidally in the ab plane. The modulation has a substantial deviation from being purely sinusoidal due to the contribution of the mentioned third harmonic.

WITHDRAWN: Effect of magnetostrictive coupling on the magnetic properties of TbFe2: ab initio study

• Elastic and magnetoelastic constants governing the amorphous TbFe 2 have been computed, and strains on crystal lattice have been studied. • Ferromagnetic interaction between Tb atoms has been found and the 111-direction is revealed to be the easy axis of the magnetization. • XMCD and XAS spectra show a large sensitivity on magnetic and elastic properties. Density functional theory (DFT) within the GGA approach is applied to investigate the electronic, elastic and magnetic properties of the amorphous TbFe 2 alloy. We found that TbFe 2 exhibits a trigonal R3̅m structure at T=0 K with lattice constants a = b = c = 5.15 Å, and α = β = γ = 60.14°. This structure can undergo elastic deformations that affect the TbFe 2 properties. The electronic properties analysis revealed a magnetic behavior and a metallic character. Therefore, to investigate the elastic and magnetic properties of TbFe 2 , the elastic and magnetoelastic constants governing the system are determined before studying the effects of applied strains on the crystal lattice. The results reveal a redistribution of Tb and Fe magnetic moments along the a-and c-axis. Moreover, a ferromagnetic interaction between the Tb atoms is found, and the [111] direction is the easy axis of the magnetization. Furthermore, the XMCD and XAS spectra of TbFe 2 in normal and deformed cases show significant magnetic and elastic properties sensitivity.

Electrophilic Trifluoromethylation of Dimetallofullerene Anions en Route to Air-Stable Single-Molecule Magnets with High Blocking Temperature of Magnetization.

Lanthanide dimetallofullerenes with single-electron M-M bonds are an important class of single molecular magnets and qubit candidates, but stabilization of their unique electronic and spin structure in the form of a neutral molecule requires functionalization of the fullerene cage with a single radical group. The lack of selectivity of the currently available procedure results in a complicated and tedious separation process. Here we demonstrate that electrophilic trifluoromethylation of a mixture of metallofullerene anions with Umemoto reagent II is highly selective toward M2@C80- (M = Tb, Y) anions, yielding M2@C80(CF3) monoadducts as the main reaction product. Single-crystal X-ray diffraction study proved attachment of the CF3 group to the pentagon/hexagon/hexagon junction and revealed that positions of metal atoms inside the fullerene cage in the cocrystal with NiOEP are strongly related to the position of the porphyrin moieties. Magnetic characterization of Tb2@C80(CF3) showed that it is a robust single-molecule magnet with broad magnetic hysteresis, 100 s blocking temperature of 25 K, and the relaxation barrier of 801(4) K, corresponding to the flipping of the Tb magnetic moment in the strongly ferromagnetically coupled [Tb3+-e-Tb3+] spin system.

Strain-induced modulation of temperature characteristics in ferrimagnetic Tb\u2013Fe films

This study investigates the effect of strain on the compensation temperature of ferrimagnetic Tb–Fe films formed on a flexible substrate. The compensation temperature is determined by the anomalous Hall measurement, and an application of 1.2% tensile strain reduces the compensation temperature by 12 K. X-ray magnetic circular dichroism reveals that approximately 5% of Fe magnetic moment and approximately 1% of Tb magnetic moment are reduced by an application of 0.9% tensile strain at the room temperature. To understand the greater reduction in Fe magnetization compared with that in Tb and the compensation temperature reduction simultaneously, a model applying molecular field theory is analyzed. Changes in three types of exchange coupling between Fe and Tb atoms are speculated to be caused by the strain.

New type of magnetic structure in the R2T2X group: Tb2Pd2In

Anisotropy of bulk magnetic properties and magnetic structure studies of a Tb2Pd2In single crystal by means of bulk magnetization methods and neutron diffraction techniques confirmed the antiferromagnetic order below the Néel temperature 29.5 K. The collinear magnetic structure of Tb magnetic moments aligned along the tetragonal c-axis is characterized by a propagation vector k = (1/4, 1/4, 1/2), yielding an equal-moment structure with alternating coupling between nearest as well as next-nearest Tb neighbors within the basal plane and antiferromagnetic coupling between the c-axis neighbors. In the context of magnetism of R2T2X compounds, where R stands for rare-earth or actinide element, such collinear structure with long-wavelength periodicity represents a new type of magnetic structure.

Multireference Ab Initio Studies of Magnetic Properties of Terbium-Based Single-Molecule Magnets.

We investigate how different chemical environments influence magnetic properties of terbium(III) (Tb)-based single-molecule magnets (SMMs), using first-principles relativistic multireference methods. Recent experiments showed that Tb-based SMMs can have exceptionally large magnetic anisotropy and that they can be used for experimental realization of quantum information applications, with a judicious choice of chemical environment. Here, we perform complete active space self-consistent field calculations including relativistic spin-orbit interaction for representative Tb-based SMMs such as TbPc2 and TbPcNc in three charge states. We calculate the low-energy electronic structure from which we compute the Tb crystal-field (CF) parameters and construct an effective pseudospin Hamiltonian. Our calculations show that the ligand type and fine points of molecular geometry do not affect the gap between the ground-state and first-excited doublets, whereas the latter varies weakly with oxidation number. On the other hand, higher-energy levels have a strong dependence on all these characteristics. For neutral TbPc2 and TbPcNc molecules, the Tb magnetic moment and ligand spin are parallel to each other and the coupling strength between them does not depend much on the ligand type and details of the atomic structure. However, ligand distortion and molecular symmetry play a crucial role in transverse CF parameters which lead to tunnel splitting. The tunnel splitting induces quantum tunneling of magnetization by itself or by combining with other processes. Our results provide insights into the mechanisms of magnetization relaxation in the representative Tb-based SMMs.

Comprehensive study of the magnetic phase transitions in Tb3Co combining thermal, magnetic and neutron diffraction measurements

A comprehensive study of the magnetic phase transitions in Tb3Co has been undertaken combining different techniques. Using single crystal neutron diffraction in the paramagnetic state a weak crystal structure distortion from the room temperature orthorhombic structure of the Fe3C type described with the Pnma space group toward structure with lower symmetry has been observed with cooling below 100 K. At 81 K there is a second order phase transition to an antiferromagnetic incommensurate phase with the propagation vector k = (0.155, 0, 0). As derived from thermal diffusivity measurements, the critical exponents for this transition are very close to the 3D-Heisenberg universality class, proving that the magnetic interactions are short-range but with a deviation from perfect isotropy due to crystal field effects. At T2 ≈ 70 K there is another magnetic phase transition to a ferromagnetic state whose character is shown to be weakly first order. The low temperature magnetic state has a non-coplanar ferromagnetic structure with strong ferromagnetic components of Tb magnetic moments along the crystallographic c-axis. The application of an external magnetic field B = 2 T along the c crystallographic axis suppresses the incommensurate antiferromagnetic phase and gives rise to the ferromagnetic phase. The magnetic entropy peak change as well as the refrigerant capacity indicate that Tb3Co is a competitive magnetocaloric material in this temperature range.

Phononic thermal Hall effect in diluted terbium oxides

We observe thermal Hall conductivity for ${({\mathrm{Tb}}_{0.3}{\mathrm{Y}}_{0.7})}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$, which is even larger than the previously observed thermal Hall conductivity for ${\mathrm{Tb}}_{2}{\mathrm{Ti}}_{2}{\mathrm{O}}_{7}$ [Science 348, 106 (2015)]. The robustness against the dilution of the Tb magnetic moment indicates the Hall effect of phonons is the origin of thermal Hall conductivity in Tb pyrochlore oxide. The temperature and magnetic field dependences are observed to follow the empirical relation that the Hall angle is proportional to the magnetization. We also investigate thermal Hall conductivity for ${({\mathrm{Tb}}_{0.3}{\mathrm{Y}}_{0.7})}_{3}{\mathrm{Ga}}_{5}{\mathrm{O}}_{12}$. We observe barely finite thermal conductivity at low temperatures. This confirms the thermal Hall conductivity in Tb-garnet oxide. The origins of the empirical relation in the pyrochlore system and the magnitude difference between the two systems are discussed comparatively with previously proposed theories of the phonon Hall effect.

Temperature dependence of the microscopic magnetization process of Tb12Co88 using magnetic Compton scattering

Abstract Tb-Co perpendicular magnetization films are mother materials for perpendicular magnetic recording media. Since the magnetic recording technique is based on magnetic switching of a material, investigating a magnetic the response of the material to a magnetic field is important. The magnetic response of the entire system is the net of each microscopic response of the spin magnetic moment and orbital magnetic moment of the elements. Herein we study the magnetization processes of the spin, orbital, and the element-specific magnetic moments by measuring the magnetic field dependence of the magnetic Compton profile of a Tb12Co88 film. The spin and orbital magnetic moments have opposite orientations. Similarly, Tb and Co magnetic moments have opposite directions. When the total magnetic moment reverses, the orientation of spin and orbital magnetization as well as Tb and Co reverse. Decreasing the temperature, the fluctuation of the magnetic moment of Tb in the perpendicular direction decreases. So the cancelation between the Tb and Co moments reduces total magnetic moment.

Existence of a critical canting angle of magnetic moments to induce multiferroicity in the Haldane spin-chain system Tb2BaNiO5

We report an unusual canted magnetism due to 3d and 4f electrons, occupying two different crystallographic sites, with its consequence to electric dipole order. This is based on neutron powder diffraction measurements on Tb2BaNiO5 (orthorhombic, Immm centrosymmetric space group), exhibiting Neel order below (TN) 63 K, to understand multiferroic behavior below 25 K. The magnetic structure is made up of Ni and Tb magnetic moments, which are found to be mutually canted in the entire temperature range below TN, though collinearity is seen within each sublattice, as known in the past. First-principles density functional theory calculations (GCA plus SO and GCA plus U plus SO approximations) support such a canted ground state. The intriguing finding, being reported here, is that there is a sudden increase in this Tb-Ni relative cantingle angle at the temperature (that is, at 25 K) at which spontaneous electric polarization sets in, with bond distance and bong angle anomalies. This finding emphasizes the need for a new spin-driven polarization mechanism, that is, a critical canting angle coupled with exchangestriction, to induce multiferroicity in magnetic insulators with canted spins.

High Blocking Temperature of Magnetization and Giant Coercivity in the Azafullerene Tb2 @C79 N with a Single-Electron Terbium-Terbium Bond.

The azafullerene Tb2@C79N is found to be a single‐molecule magnet with a high 100‐s blocking temperature of magnetization of 24 K and large coercivity. Tb magnetic moments with an easy‐axis single‐ion magnetic anisotropy are strongly coupled by the unpaired spin of the single‐electron Tb−Tb bond. Relaxation of magnetization in Tb2@C79N below 15 K proceeds via quantum tunneling of magnetization with the characteristic time τ QTM=16 462±1230 s. At higher temperature, relaxation follows the Orbach mechanism with a barrier of 757±4 K, corresponding to the excited states, in which one of the Tb spins is flipped.

Spin reorientation and magnetoelastic properties of ferromagnetic Tb1−xNdxCo2 systems with a morphotropic phase boundary

The spin reorientation (SR) and magnetoelastic properties of pseudobinary ferromagnetic $\mathrm{T}{\mathrm{b}}_{1\ensuremath{-}x}\mathrm{N}{\mathrm{d}}_{x}\mathrm{C}{\mathrm{o}}_{2}$ ($0\ensuremath{\le}x\ensuremath{\le}1.0$) systems involving a morphotropic phase boundary (MPB) were studied by high-resolution synchrotron x-ray diffraction (XRD), magnetization, and magnetostriction measurements. The easy magnetization direction of the Laves phase lies along the $\ensuremath{\langle}111\ensuremath{\rangle}$ axis with $xl0.65$, whereas it lies along the $\ensuremath{\langle}100\ensuremath{\rangle}$ axis for $xg0.65$ below Curie temperature (${T}_{\mathrm{C}}$). The temperature-dependent magnetization curves showed SR; this can be explained by a two-sublattice model. Based on the synchrotron (XRD) and magnetization measurements, the SR phase diagram for a MPB composition of $\mathrm{T}{\mathrm{b}}_{0.35}\mathrm{N}{\mathrm{d}}_{0.65}\mathrm{C}{\mathrm{o}}_{2}$ was obtained. Contrary to previously reported ferromagnetic systems involving MPB, the MPB composition of $\mathrm{T}{\mathrm{b}}_{0.35}\mathrm{N}{\mathrm{d}}_{0.65}\mathrm{C}{\mathrm{o}}_{2}$ exhibits a low saturation magnetization (${M}_{\mathrm{S}}$), indicating a compensation of the Tb and Nd magnetic moments at MPB. The anisotropic magnetostriction (${\ensuremath{\lambda}}_{\mathrm{S}}$) first decreased until $x=0.8$ and then continuously increased in the negative direction with further increase of Nd concentration. The decrease in magnetostriction can be attributed to the decrease of spontaneous magnetostriction ${\ensuremath{\lambda}}_{111}$ and increase of ${\ensuremath{\lambda}}_{100}$ with opposite sign to ${\ensuremath{\lambda}}_{111}$. This paper indicates an anomalous type of MPB in the ferromagnetic $\mathrm{T}{\mathrm{b}}_{1\ensuremath{-}x}\mathrm{N}{\mathrm{d}}_{x}\mathrm{C}{\mathrm{o}}_{2}$ system and provides an active way to design novel functional materials with exotic properties.

Zero Thermal Expansion in Magnetic and Metallic Tb(Co,Fe)2 Intermetallic Compounds.

Due to the advantage of invariable length with temperatures, zero thermal expansion (ZTE) materials are intriguing but very rare especially for the metals based compounds. Here, we report a ZTE in the magnetic intermetallic compounds of Tb(Co,Fe)2 over a wide temperature range (123-307 K). A negligible coefficient of thermal expansion (αl = 0.48 × 10-6 K-1) has been found in Tb(Co1.9Fe0.1). Tb(Co,Fe)2 exhibits ferrimagnetic structure, in which the moments of Tb and Co/Fe are antiparallel alignment along the c axis. The intriguing ZTE property of Tb(Co,Fe)2 is formed due to the balance between the negative contribution from the Tb magnetic moment induced spontaneous magnetostriction and the positive role from the normal lattice expansion. The present ZTE intermetallic compounds are also featured by the advantages of wide temperature range, high electrical conductivity, and relatively high thermal conductivity.

Investigation and Effective Control of Perpendicular Magnetic Anisotropy for TbCo Films with Different Underlayers

We performed a detailed study on the perpendicular magnetic anisotropy (PMA) of TbCo film by using two kinds of nonmagnetic underlayers, Ta and Ta/Cu with different thicknesses. We found that for both the Tb-rich and Co-rich TbCo alloy films, the PMA strength decreases considerably with the increase of Ta underlayer thickness, while their net saturation magnetization [Formula: see text] exhibit opposite varying trends. The [Formula: see text] value continues to increase for the Co-rich TbCo samples while decrease for the Tb-rich films. Interestingly, an additional Cu layer inserted between the Ta and TbCo layers can efficiently recover the PMA and [Formula: see text]. We attribute such observed variation behaviors of magnetic properties to the increased disordering of Tb magnetic moments at the Ta/TbCo interface, which has been verified by both experimental measurements and micromagnetic simulations.

Anomalous Hall effect studies on Tb–Fe thin films

TbxFe100−x (with x=11, 25, 31 and 44) thin films were prepared with the substrates kept at a temperature of 300°C and the Hall resistivities and electrical resistivities were investigated in the temperature range 25–300K. The sign of Hall resistivity is found to change from positive for x=31 to negative for x=44 film at temperatures 25K and 300K, reflecting the compensation of Tb and Fe magnetic moments between these two compositions. Perpendicular magnetic anisotropy was observed in the films of x=25 and 31 at 25K as well as at 300K. The Hall resistivity is seen to increase for the films of x=11 and 31 with increasing temperature, while it decreases for the films of x=25 and 44 with increasing temperature. The temperature coefficients of electrical resistivities of these films are seen to be positive. The presence of perpendicular magnetic anisotropy (refers to magnetic anisotropy, in this paper) in the temperature range 25–300K in Tb25Fe75 and Tb31Fe69 and their metallic nature are indicators that the Tb–Fe films deposited at higher temperatures are more suitable for magneto optic data storage applications than their amorphous counterparts, due to the stability of the former.

Structural, Magnetic, and Optoelectronic Properties of TbNi5, TbNi3Ti2 and TbNi3V2 Compounds

The spin-polarized, electronic, magnetic, and optical properties of TbNi5, TbNi3Ti2, and TbNi3V2 intermetallic compounds have been calculated by employing the full-potential linear augmented plane waves (FP-LAPW) within the density functional theory (DFT) and implemented in the WIEN2k package. In this approach, the generalized gradient approximation with Hubbard U-correction (GGA + U) was chosen as exchange-correlation potential. The electronic structure such as band structure and density of states have been investigated and compared among them. The frequency dependences of dielectric function, optical absorption, reflectivity, and optical conductivity are determined. The optical spectra are changed due to the substitution of nickel with titanium and vanadium. Total and local magnetic moments of Tb, Ni, Ti, and V are also estimated; it is shown that the total magnetic moment of the three alloys is vigorously contributed by the local magnetic moment of terbium.