Easy-axis Magnetic Anisotropy Research Articles

Spin waves in antiferromagnetically coupled bilayers of transition-metal dichalcogenides with Dzyaloshinskii–Moriya interaction

In this paper we analyse quantized spin waves (also referred to as magnons) in bilayers of two-dimensional van der Waals materials, like Vanadium-based dichalcogenides, VX2 (X = S, Se, Te) and other materials of similar symmetry. We assume that the materials exhibit Dzyaloshinskii–Moriya interaction and in-plane easy-axis magnetic anisotropy due to symmetry breaking induced externally (e.g. by strain, gate voltage, proximity effects to an appropriate substrate/oberlayer, etc.). The considerations are limited to a collinear spin ground state, stabilized by a sufficiently strong in-plane magnetic anisotropy. The theoretical analysis is performed within the general spin wave theory based on the Holstein–Primakoff–Bogoliubov transformation. Accordingly, the description takes into account quantum antiferromagnetic fluctuations. However, it is limited to linear spinwave modes. The Dzyaloshinskii–Moriya interaction is shown to modify the spin wave spectrum of the bilayers, making its low energy part qualitatively similar to the electronic spectrum of the Rashba spin–orbit model.

Skyrmion crystal formation and temperature–magnetic-field phase diagram of the frustrated triangular lattice Heisenberg magnet with easy-axis magnetic anisotropy

Skyrmion crystal formation and temperature–magnetic-field phase diagram of the frustrated triangular lattice Heisenberg magnet with easy-axis magnetic anisotropy

Coordination number impact on magnetic properties of Schiff base Co(II) complexes

Two mononuclear Co(II) complexes with a tetrahedral and octahedral coordination geometry with a Schiff base ligand L− (anion of 4-[(2-fluoroanilino)-phenyl-methylene]-5-methyl-2-phenyl-pyrazol-3-one) having the formulas [CoL2]·2MeCN (1) and [CoL2(H2O)2]·2MeCN (2) have been synthesized and structurally characterized. Notably, their coordination geometry and magnetic relaxation behaviors can be tuned by variation of reaction conditions. Static magnetic studies reveal that complex 1 exhibits considerable easy-axis magnetic anisotropy. Frequency-dependent susceptibility measurements revealed slow magnetic relaxation behavior with spin-reversal barriers of 79.2 K at an applied external field of 500 Oe. Clear magnetic hysteresis loops were observed for 1 at 2 K. Complex 2 show field-induced slow magnetic relaxation with Raman and direct relaxation processes. The observed magnetic behavior of 1 and 2 is confirmed by high-level ab initio calculations and simulation of χMT(T) curves.

Thermal evolution of spin excitations in honeycomb Ising antiferromagnetic FePSe3

We use elastic and inelastic neutron scattering (INS) to study the antiferromagnetic (AF) phase transitions and spin excitations in the two-dimensional (2D) zig-zag antiferromagnet FePSe3. By determining the magnetic order parameter across the AF phase transition, we conclude that the AF phase transition in FePSe3 is first-order in nature. In addition, our INS measurements reveal that the spin waves in the AF ordered state have a large easy-axis magnetic anisotropy gap, consistent with an Ising Hamiltonian, and possible biquadratic magnetic exchange interactions. On warming across TN, we find that dispersive spin excitations associated with three-fold rotational symmetric AF fluctuations change into FM spin fluctuations above TN. These results suggest that the first-order AF phase transition in FePSe3 may arise from the competition between C3 symmetric AF and C1 symmetric FM spin fluctuations around TN, in place of a conventional second-order AF phase transition.

Magnetic Anisotropy and Relaxation in Four-Coordinate Cobalt(II) Single-Ion Magnets with a [CoIIO4] Core.

A mononuclear four-coordinate Co(II) complex with a [CoIIO4] core, namely, PPN[Li(MeOH)4][Co(L)2] (1) (PPN = bis(phosphoranediyl)iminium; H2L = perfluoropinacol), has been studied by X-ray crystallography, magnetic characterization, and theoretical calculations. This complex presents a severely distorted coordination geometry. The O-Co-O bite angle is 83.42°/83.65°, and the dihedral twist angle between the O-Co-O chelate planes is 55.6°. The structural distortion results in a large easy-axis magnetic anisotropy with D = -104(1) cm-1 and a transverse component with |E| = +4(2) cm-1. Alternating current (ac) susceptibility measurements demonstrate that 1 exhibits slow relaxation of magnetization at zero static field. However, the frequency-dependent out-of-phase (χ"M) susceptibilities of 1 at 0 Oe do not show a characteristic maximum. Upon the application of a dc field or the dilution with a diamagnetic Zn matrix, the quantum tunneling of magnetization (QTM) process can be successfully suppressed. Notably, after dilution with the Zn matrix, the obtained sample exhibits a structure different from that of the pristine complex. In this altered sample, the asymmetric unit does not contain the Li(MeOH)4+ cation, resulting in an O-Co-O bite angle of 86.05° and a dihedral twist angle of 75.84°, thereby leading to an approximate D2d symmetry. Although such differences are not desirable for magnetic studies, this study still gives some insights. Theoretical calculations reveal that the D parameter is governed by the O-Co-O bite angle, in line with our previous report for other tetrahedral Co(II) complex with a [CoIIN4] core. On the other hand, the rhombic component is found to increase as the dihedral angle deviates from 90°. These findings provide valuable guidelines for fine-tuning the magnetic properties of Co(II) complexes.

Tailoring single-ion magnet properties of coordination polymer C11H18DyN3O9 (Dy-CP) using the radial effective charge model (RECM) and superposition model (SPM).

We investigate Dy-based coordination polymer C11H18DyN3O9 (Dy-CP) exhibiting single-ion magnet (SIM) properties, e.g., quantum tunnelling of magnetization (QTM), magnetic anisotropy, magnetic relaxation, and effective energy barrier (Ueff). To elucidate the underlying mechanisms, crystal field parameters (CFPs) for Dy3+ ions were modelled using the radial effective charge model (RECM) and superposition model (SPM), and the computational packages SIMPRE and SPECTRE. The modelled CFPs enable the prediction of the energy levels and associated wave functions, which successfully explain the field-induced Dy-CP SIM properties. The so-calculated magnetic susceptibility and isothermal magnetization match the experimental data reasonably well. The smaller energy separations of the first (Δ0-1 ∼ 31 cm-1) and the second (Δ0-2 = 74 cm-1) excited Kramers doublets suggest small Ueff = 65 cm-1 for Dy-CP. The magnetic moments of Dy3+ ions exhibit an easy-axis type magnetic anisotropy in the ground state, but change orientation in the excited states due to mixing of states from different Kramers doublets. Low-symmetry CF components play a crucial role in connecting different |±MJ〉 states within the ground multiplet, resulting in QTM and magnetic relaxation to the ground state occurring via the excited states. The RECM and SPM calculated CFP sets are standardized employing the 3DD package to enable meaningful comparison and assessing their mutual equivalence. The results demonstrate the correlation between structural and electronic features of the molecule and site symmetry and distortion of the local coordination polyhedra with SIM properties, offering insights for rational design of new SIMs. The importance of considering low-symmetry aspects in CFP modelling for accurate predictions of magnetic properties is highlighted. This study provides deeper understanding of field-induced behaviour in rare-earth-based SIMs and approaches for rationalization of experimentally measured SIMs' properties.

Control of the geometry and anisotropy driven by the combination of steric and anion coordination effects in CoII complexes with N6-tripodal ligands: the impact of the size of the ligand on the magnetization relaxation time.

Four mononuclear CoII complexes of formula [Co(L)(SCN)2(CH3OH)0.5(H2O)0.5]·1.5H2O·0.75CH3OH (1), [Co(L1)Cl2]·H2O·2CH3CN (2), [Co(L1)(SCN)2]·1.5H2O·CH3OH (3) and [Co(L1)]ClO4·2CH3OH (4) were prepared from the N6-tripodal Schiff base ligands (S)P[N(Me)NC(H)2-Q]3 (L) and (S)P[N(Me)NC(H)1-ISOQ]3 (L1), where Q and ISOQ represent quinolyl and isoquinolyl moieties, respectively. In 1, the L ligand does not coordinate to the CoII ion in a tripodal manner but using a new N,N,S tridentate mode, which is due to the fact that the N6-tripodal coordination promotes a strong steric hindrance between the quinolyl moieties. However, L1 can coordinate to the CoII ions either in a tripodal manner using CoII salts with poorly coordinating anions to give 4 or in a bisbidentate fashion using CoII salt-containing medium to strongly coordinating anions to afford 2 and 3. In the case of L1, there is no steric hindrance between ISOQ moieties after coordination to the CoII ion. The CoII ion exhibits a distorted octahedral geometry for compounds 1-3, with the anions in cis positions for the former and in trans positions for the two latter compounds. Compound 4 shows an intermediate geometry between an octahedral and trigonal prism but closer to the latter one. DC magnetic properties, HFEPR and FIRMS measurements and ab initio calculations demonstrate that distorted octahedral complexes 1-3 exhibit easy-plane magnetic anisotropy (D > 0), whereas compound 4 shows large easy-axis magnetic anisotropy (D < 0). Comparative analysis of the magneto-structural data underlines the important role that is played not only by the coordination geometry but also the electronic effects in determining the anisotropy of the CoII ions. Compounds 2-3 show a field-induced slow relaxation of magnetization. Despite its large easy-axis magnetic anisotropy, compound 4 does not show significant slow relaxation (SMR) above 2 K under zero applied magnetic fields, but its magnetic dilution with ZnII triggers SMR at zero field. Finally, it is worth remarking that compounds 2-4 show smaller relaxation times than the analogous complexes with the tripodal ligand bearing in its arms pyridine instead of isoquinoline moieties, which is most likely due to the increase of the molecular size in the former one.

Role of Inter-site Hubbard Interactions in MnS Monolayer: DFT+U+V Investigation

The stable MnS monolayer was recently predicted using first-principles density functional theory (DFT) including Hubbard U (DFT+U) correction and Monte Carlo (MC) simulations. It is shown to exhibit an indirect band gap of 0.68 eV semiconductor with a high Neel temperature (T_N) of 720 K and an in-plane easy axis magnetic anisotropy energy (MAE). The considered on-site Hubbard U correction takes into account only the Mn (3d) localized nature. To correct the inter-site errors due to strong hybridization between bonded Mn (3d) and S (2p) states, the Hubbard +V inter-site parameter should be added to the calculations. In this study, the band gap of MnS is found to be increased to 1.24 eV (twice that for DFT+U) after considering the inter-site V correction (DFT+U+V). Since the MnS monolayer prefers an in-plane easy axis for the MAE, the estimated Berezinskii Kosterlitz Thouless transition (BKT) transition temperature is as high as 1667.8 K. The carrier mobility is calculated based on the deformation potential and effective mass and it is found that holes (2.12 〖cm〗^2 v^(-1) S^(-1)) are twice the size of these electrons (1.21 〖cm〗^2 v^(-1) S^(-1)). The results are expected to improve the potential of the MnS monolayers in multiple AFM spintronic device applications.

Formation of a single-ion magnet in the lanthanum calcium silicate apatite structure by the cobalt oxide doping

A small amount of cobalt was incorporated into the lanthanum calcium silicate apatite structure by annealing at 1500 °C in argon. The compound exhibits easy-axis magnetic anisotropy with a zero-field splitting parameter 2D of −60 cm−1 and field- induced slow relaxation of magnetization with a remagnetization energy barrier of 58–63 cm−1. Thereby, for the first time, a cobalt-based single-ion magnet was created in silicate.

Syntheses, Structures, and Magnetic Properties of Three Cyano-Bridged FeII-MoIII Single-Molecule Magnets.

Three new cyano-bridged FeII-MoIII complexes assembled from the [MoIII(CN)7]4- unit, FeII ions, and three pentadentate N3O2 ligands, namely {[Fe2H3(dapab)2][Mo(CN)6]}n·2H2O·3.5MeCN (1), [Fe(H2dapb)(H2O)][Fe(Hdapb)(H2O)][Mo(CN)6]·4H2O·3MeCN (2), and [Fe(H2dapba)(H2O)]2[Mo(CN)7]·6H2O (3) (H2dapab = 2,6-diacetylpyridine bis(2-aminobenzoylhydrazone), H2dapb = 2,6-diacetylpyridine bis(benzoylhydrazone), H2dapba = 2,6-diacetylpyridine bis(4-aminobenzoylhydrazone)), have been synthesized and characterized. Single-crystal structure analyses suggest that complex 1 contains a one-dimensional (1D) chain structure where two FeII ions are bridged by the in situ generated [MoIII(CN)6]3- unit through two trans-cyanide groups into trinuclear Fe2IIMoIII clusters that are further linked by the amino of the ligand into an infinite chain. Complexes 2 and 3 are cyano-bridged Fe2IIMoIII trinuclear clusters with two FeII ions connected by the [MoIII(CN)6]3- and [MoIII(CN)7]4- units, respectively. Direct current magnetic studies confirmed the ferromagnetic interactions between the cyano-bridged FeII and MoIII centers and significant easy-axis magnetic anisotropy for all three complexes. Furthermore, complexes 1-3 exhibit slow magnetic relaxation under a zero dc field, with relaxation barriers of 42.3, 21.6, and 14.4 K, respectively, making them the first examples of cyano-bridged FeII-MoIII single-molecule magnets.

Spatial Spin-Modulated Structure of Bi1 – xSrxFeO3 – y (x = 0, 0.05, and 0.10) Multiferroics

The room-temperature X-ray and Mössbauer data on the BiFeO3, Bi0.95Sr0.05FeO3 – y, and Bi0.90Sr0.10FeO3 – y multiferroics obtained by solid-phase synthesis are presented. The samples have a rhombohedral crystal structure with the sp. gr. R3c. The lattice parameter ah is invariable, while the parameter ch decreases with increasing strontium content. The 57Fe Mössbauer spectra recorded at a temperature of 295 K have been interpreted within the cycloid spatial spin-modulated structure model. It has been established that the easy-axis magnetic anisotropy is implemented in the investigated multiferroics. The anharmonicity parameter m of the spin-modulated structure has been measured. Upon replacement of trivalent Bi3+ ions in small amounts (x = 0–0.10) with divalent Sr2+ ions, the parameter m increases by a factor of more than 3: from 0.10(4) at x = 0.00 to 0.36(10) at x = 0.10.

Field-induced Co(II) single-ion magnet in octahedral [S6] coordination environment

The soft donor ligands are of great importance to the pursuit of 3d transition-metal complexes with large magnetic anisotropy. Herein, a soft tripodal ligand, hydrotris(mercaptobenzothiazolyl)borate (Tbz) was used to construct a high-spin mononuclear complex [CoII(Tbz)2] (1), having an octahedral geometry in an S6 donor set. The combination of direct-current (dc) magnetic susceptibility and Low-temperature high-field electron paramagnetic resonance (HFEPR) reveals the easy-axis magnetic anisotropy of 1. Complex 1 shows field-induced slow relaxation of magnetization at an applied magnetic field of 1000 Oe, indicating the behavior of single-molecule magnet. The foregoing result constitutes the first instance of Co(II)-based single-ion magnet containing a CoS6 unit.

Hydrogen-bonded nickel(II)-organosulfonate framework: Thermal expansion behavior, proton conduction, and magnetic properties

Metalo Hydrogen-bonded organic frameworks are emerging supramolecular platforms for designing functional molecular materials. Herein, we reported the supramolecular structure, thermal, magnetic, and proton conduction properties of a hydrogen-bonded nickel(II)-organosulfonate framework, [Ni(H2O)6][NPS]2 (NiHOF, HNPS = naphthalene-2-sulphonic acid). Single-crystal X-ray diffraction studies reveal a two-dimensional hydrogen-bonded network sustained by multiple and charge-assisted OH···O H bonds between hexaaquanickel(II) cations and organosulfonate anions. Additionally, continuous ca. 0.47 × 0.70 nm2 windows were formed within the framework. The thermal stability of the NiHOF was confirmed by thermal gravimetric analysis and variable temperature single-crystal and powder X-ray diffraction patterns. N2 sorption isotherms suggest an ultramicroporous supramolecular framework of NiHOF with permanent porosity. The anisotropic positive thermal expansion behavior of NiHOF was evidenced by the dynamic crystallography experiments. Magnetic measurements indicate easy-axis magnetic anisotropy (D = -10.5 cm−1) of the NiHOF while no slow magnetic relaxation behavior. Electrochemical impedance spectroscopy indicates the temperature and humidity dependence of conductivities of NiHOF. At 50 °C and 70% relative humidity, the conductivity is 1.13 × 10−4 S·cm−1, revealing a supramolecular proton conductor of NiHOF. This work provides a potential way for designing novel thermal, magnetic, and electrical molecular materials through the supramolecular assembly of inorganic and organosulfonate synthons.

Ab initio exploration of short-pitch skyrmion materials: Role of orbital frustration

In recent years, the skyrmion lattice phase with a short lattice constant has attracted attention due to its high skyrmion density, making it a promising option for achieving high-density storage memory and for observing novel phenomena like the quantized topological Hall effect. Unlike conventional non-centrosymmetric systems where the Dzyaloshinsky–Moriya interaction plays a crucial role, the short pitch skyrmion phase requires a quadratic magnetic interaction J(q) with a peak at finite-Q, and weak easy-axis magnetic anisotropy is also critical. Thus, conducting first-principles evaluations is essential for understanding the formation mechanism as well as for promoting the discovery of new skyrmion materials. In this Perspective, we focus on recent developments of the first-principles evaluations of these properties and apply them to the prototype systems GdT2X2 and EuT2X2, where T denotes a transition metal and X represents Si or Ge. In particular, based on the spin density functional theory with the Hubbard correction combined with the Liechtenstein method in the Wannier tight-binding model formalism, we first show that the Hubbard U and Hund’s coupling is essential to stabilize a skyrmion lattice state by enhancing the easy-axis anisotropy. We then discuss mechanisms of finite-Q instability and show that competition among Gd-5d orbitals determines whether ferromagnetism or a finite-Q structure is favored in GdT2Si2 with T= Fe and Ru. Our systematic calculations reveal that GdRu2X2, GdOs2X2, and GdRe2X2 are promising, while GdAg2X2, GdAu2X2, and EuAg2X2 are possible candidates as the skyrmion host materials. Analysis based on a spin spiral calculation for the candidate materials is also presented.

Proton-conducting cobalt(II) hydrogen-bonded organic framework driven by coordinated water molecules with slow magnetic relaxation

Metal hydrogen-bonded organic framework (MHOF) has received ongoing attention because they provide new chances for the design and construction of functional molecular materials. Herein, we reported a rare dual-functional MHOF based on a mononuclear complex, [Co(QLC)2·(H2O)2] (1, HQLC = Quinoline-2-carboxylic acid) with interesting magnetic and electrical properties. Variable-temperature single-crystal diffraction experiments revealed a highly thermal stable three-dimensional (3D) hydrogen-bonded network supported by multiple intermolecular hydrogen bonding and π–π stacking interactions. Importantly, the metal-bound water molecules were found to be critical for the formation of H-bonded 2D layers with the contribution of terminal carboxylic oxygen of QLC. By taking advantage of the enhanced acidity of the coordinated water molecules, variable-temperature and -humility alternating current impedance spectroscopy revealed the compound is a good supramolecular proton conductor with 1.2 × 10−4 S·cm−1 at 70 °C under 97% RH. D.C. susceptibility measurement indicated easy-axis magnetic anisotropy of the Co2+ ions with the experimental D value of -72.1 cm−1 in the complex. Dynamic A.C. susceptibility measurements revealed the compound can display slow magnetic relaxation under an applied dc field. The foregoing results provide not only a rare hydrogen-bonded organic−cobalt framework displaying interesting magnetic and electrical properties but also a promising way to build multifunctional MHOFs via coordinated water molecules.

Incorporating Highly Anisotropic Four-Coordinate Co(II) Ions within One-Dimensional Coordination Chains

Low-coordinate metallic ions have been well recognized for constructing good-performance single ion magnets (SIMs) due to their enhanced magnetic anisotropy; however, the incorporation of such specific ions into coordination polymers is still challenging. Here, we reported two new CoII coordination polymers, namely [Co(pdms)(bpe)]n (1) and {[Co(pdms)(tpb)]·H2O·tpb}n (2) (H2pdms = 1,2-bis(methanesulfonamido)benzene, bpe = 1,2-di(4-pyridyl)ethane, tpb = 1,2,4,5-tetra(4-pyridyl)benzene). Single crystal X-ray diffraction experiments indicated that the CoII centers in both 1 and 2 display a distorted tetrahedral geometry with quasi C2v symmetry and are linked into a one-dimensional (1D) zig-zag chain via the ditopic bridging ligand of bpe in 1 while a ribbon chain via the tetradentate linker of tpb in 2. Magnetic studies revealed the easy-axis magnetic anisotropy of the CoII ions with different zero-field splitting D of −19 cm–1 (1) and −33 cm–1 (2), likely due to the distinct changes in the Npy–Co–Npy bite angles (100.20° (1) vs. 93.90° (2)). Moreover, slow magnetic relaxation proceeded via different relaxation mechanisms under applied dc fields was observed, giving an effective energy barrier (Ueff) of 69.6 K for 1 and 76.6 K for 2, respectively. The ab initio calculations on both the polymers further confirmed the sign and magnitude of the ZFS parameters and nicely reproduced the experimental results. Our study demonstrated a great potential for applying the well-studied and highly anisotropic 4-coordinate metal ions within a coordination polymer, opening a viable means to tuning magnetic anisotropy via topological control.

Ancillary Ligand Coordination Directed Modes of Aggregation in Mixed-Valence Tetranuclear Cobalt Complexes: Synthesis, Structure, Field-Induced SIM Behavior, and Theoretical Insights

The contrasting metal–ion coordination reactivity behavior for the multisite ligand H3L ([2,6-bis-{(2-hydroxymethyl-phenylimino)methyl}-4-methylphenol]) with Co(ClO4)2·6H2O in the presence of ancillary ligands NaPiv (Piv = (CH3)3CCO2–) and NH4SCN afforded two different types of mixed-valence tetranuclear cobalt complexes, [CoIII3CoII(HL)(L)(μ4-O)(μ-OH)((CH3)3CCOO)2]ClO4·H2O (1) and [CoIII2CoII2(L)2(NCS)4(CH3CN)2]·CH3CN (2). In the first case, the presence of bridging pivalate anions triggered the oxido-hydroxido-bridged dual control for aggregation, whereas in the second case, terminal thiocyanate coordination forced the dicubane type of aggregation. The connectivity for different numbers of CoIII and CoII ions are achieved through contrasting bridges by ancillary water-molecule-derived HO– plus O2– linkers and ligand-anion-based double phenolato bridges, where terminal monodentate coordinations finally fulfill the octahedral geometries around the CoII ions. Alternating current/direct current (AC/DC) magnetic studies revealed field-induced slow magnetic relaxation for complex 1 that arises from the single octahedral CoII ion connected to three other diamagnetic CoIII ions. Whereas in complex 2, having a tetranuclear CoIII2CoII2 structure, the two CoII centers showed an antiferromagnetic interaction (J = −0.39 cm–1). The structural distortions in these two types of aggregates lead to different magnitudes of easy-axis magnetic anisotropy (D = −51.31 cm–1 for 1 and −31.9 cm–1 for 2) and a small but non-negligible transverse component (E/D = 0.263 for 1 and 0.255 for 2). The static and dynamic magnetic data were analyzed using DFT and CASSCF-based calculations.

Easy-axis magnetic anisotropy in tetragonally elongated cobalt(II) complexes beyond the spin-Hamiltonian formalism.

Two hexacoordinate Co(II) complexes [Co(hfac)2(etpy)2] (1) and [Co(hfac)2(bzpyCl)2] (2) were synthesized and spectrally and structurally characterized. The {CoO4N2} chromophore adopts a geometry of the elongated tetragonal bipyramid with a small o-rhombic component. This less common arrangement causes the magnetic data to need be analysed using the Griffith-Figgis model, instead of the commonly used spin-Hamiltonian with zero-field splitting parameters D and E. In the case of the elongated bipyramid for d7 complexes, the source of the magnetic anisotropy of an easy-axis type is the axial crystal field splitting Δax. The ab initio CASSCF calculations followed by the NEVPT2 module confirm that the ground electronic term is quasi-degenerate owing to the splitting of the 4Eg (D4h) mother term. The lowest spin-orbit multiplets appear as four Kramers doublets belonging to the Γ5 irreducible representation of the double point group D2'. They exhibit a serious mixing of the |±1/2〉 and |±3/2〉 spins which reflects a sizable effect of the spin-orbit coupling. Both complexes exhibit field-supported slow magnetic relaxation governed by the Raman process.

Pushing up the easy-axis magnetic anisotropy and relaxation times in trigonal prismatic CoII mononuclear SMMs by molecular structure design.

The replacement of pyridine by 1-methyl-imidazol in the arms of a N6-tripodal ligand allows preparing two new CoII complexes with quasi-ideal triangular prismatic geometry, which behave as SIMs (Single Ion Magnets) at zero dc field with enhanced axial magnetic anisotropy, magnetic relaxation times and magnetic hysteresis.

Competing Easy-Axis Anisotropies Impacting Magnetic Tunnel Junction-Based Molecular Spintronics Devices (MTJMSDs).

Molecular spintronics devices (MSDs) attempt to harness molecules' quantum state, size, and configurable attributes for application in computer devices-a quest that began more than 70 years ago. In the vast number of theoretical studies and limited experimental attempts, MSDs have been found to be suitable for application in memory devices and futuristic quantum computers. MSDs have recently also exhibited intriguing spin photovoltaic-like phenomena, signaling their potential application in cost-effective and novel solar cell technologies. The molecular spintronics field's major challenge is the lack of mass-fabrication methods producing robust magnetic molecule connections with magnetic electrodes of different anisotropies. Another main challenge is the limitations of conventional theoretical methods for understanding experimental results and designing new devices. Magnetic tunnel junction-based molecular spintronics devices (MTJMSDs) are designed by covalently connecting paramagnetic molecules across an insulating tunneling barrier. The insulating tunneling barrier serves as a mechanical spacer between two ferromagnetic (FM) electrodes of tailorable magnetic anisotropies to allow molecules to undergo many intriguing phenomena. Our experimental studies showed that the paramagnetic molecules could produce strong antiferromagnetic coupling between two FM electrodes, leading to a dramatic large-scale impact on the magnetic electrode itself. Recently, we showed that the Monte Carlo Simulation (MCS) was effective in providing plausible insights into the observation of unusual magnetic domains based on the role of single easy-axis magnetic anisotropy. Here, we experimentally show that the response of a paramagnetic molecule is dramatically different when connected to FM electrodes of different easy-axis anisotropies. Motivated by our experimental studies, here, we report on an MCS study investigating the impact of the simultaneous presence of two easy-axis anisotropies on MTJMSD equilibrium properties. In-plane easy-axis anisotropy produced multiple magnetic phases of opposite spins. The multiple magnetic phases vanished at higher thermal energy, but the MTJMSD still maintained a higher magnetic moment because of anisotropy. The out-of-plane easy-axis anisotropy caused a dominant magnetic phase in the FM electrode rather than multiple magnetic phases. The simultaneous application of equal-magnitude in-plane and out-of-plane easy-axis anisotropies on the same electrode negated the anisotropy effect. Our experimental and MCS study provides insights for designing and understanding new spintronics-based devices.