Search Results (177)

Given the outstanding magnetic characteristics of lanthanide ions, the development of mononuclear or multinuclear lanthanide complexes becomes imperative. Previous research showed that a series of mononuclear Dy(III) complexes of rhodamine benzoyl hydrazone Schiff base ligands exhibit remarkable single-molecule magnetic properties and fluorescence. In this study, we used analogous ligands to synthesize lanthanide complexes [Dy(HL¹-o)(NO₃)₂(CH₃OH)₂]NO₃·CH₃OH (complex 1·MeOH) and tetranuclear complexes [Ln₄(L¹-c)₂(L²)₂(μ₃-OH)₂(NO₃)₂(CH₃OH)₄](NO₃)₂·2CH₃CN·5CH₃OH·2H₂O (Ln = Dy, complex 2; Ln = Gd, complex 3). Magnetic susceptibility measurements show that 1·2H₂O is a single-molecule magnet, 2 shows slow magnetic relaxation and 3 is a magnetic cooling material with the magnetic entropy change of 9.81 J kg⁻¹ K⁻¹ at 2 K and 5 T. The theoretical calculations on 1·MeOH indicate that it shows good magnetic anisotropy with the calculated energy barrier of 194.6 cm⁻¹. Full article

Magnetic nanowires with domain walls (DWs) play a crucial role in the advancement of next-generation memory and spintronic devices. Understanding the thermal effects on domain wall behavior is essential for optimizing performance and stability. This study investigates the thermal chirality-dependent dynamics and pinning of transverse domain walls (TDWs) in Z-junction nanowires using micromagnetic simulations. The analysis focuses on head-to-head (HHW) and tail-to-tail (TTW) domain walls with up and down chirality under varying thermal conditions. The results indicate that higher temperatures reduce the pinning strength and depinning current density, leading to enhanced domain wall velocity. At 200 K, the HHW_down domain wall depins at a critical current density of 1.2 × 10¹¹ A/m², while HHW_up requires a higher depinning temperature, indicating stronger pinning effects. Similarly, the depinning temperature (T_d) increases with Z-junction depth (d), reaching 300 K at d = 50 nm, while increasing Z-junction (λ) weakens pinning, reducing T_d to 150 K at λ = 50 nm. Additionally, the influence of Z-junction geometry and magnetic properties, such as saturation magnetization (M_s) and anisotropy constant (K_u), is examined to determine their effects on thermal pinning and depinning. These findings highlight the critical role of chirality and thermal activation in domain wall motion, offering insights into the design of energy-efficient, high-speed nanowire-based memory devices. Full article

In this research, an analysis of the thermomagnetic properties of a nanoscale spin-2 and spin-3/2 system is conducted. This system is modeled with as a quasi-spherical Ising-type nanoparticle with a diameter of 2 nm, in which atoms with spin-2 and spin-3/2 configured in body-centered cubic (BCC) lattices interact within their relevant nanostructures. To determine the thermomagnetic behaviors of the nanoparticle, numerical simulations using Monte Carlo techniques and thermal bath class algorithms are performed. The results exhibit the effects of exchange couplings ($J_1,J_2^{\prime }$), magnetocrystalline anisotropies ($D_{3/2}^{\prime },D_2^{\prime }$), and external magnetic fields ($h^{\prime }$) on the finite-temperature phase diagrams of magnetization ($M_T$), magnetic susceptibility (${\chi }_T$), and thermal energy ($k_B{T}^{\prime }$). The influences of the exchange, anisotropic, and external field parameters are clearly reflected in the compensation, hysteretic, and pseudocritical phenomena presented by the quasi-spherical nanoparticle. When the parameter reflecting ferromagnetic second-neighbor exchanges in the nanosphere ($J_2^{\prime }$) increases, for a given value of the external magnetic field, the compensation ($T_{comp}$) and pseudocritical ($T_{pc}$) temperatures increase. Similarly, in the ranges $0<J_2^{\prime }⩽4.5$ and $-15⩽h^{\prime }⩽15$ at a specific temperature, an increase in $J_2^{\prime }$ results in the appearance of exchange anisotropies (exchange bias) and and increased hysteresis loop areas in the nanomodel. Full article

Permanent magnetic materials are essential for technological applications, with the majority of available magnets being either ferrites or materials composed of critical rare-earth elements, such as well-known Nd₂Fe₁₄B. The binary Fe₂P material emerges as a promising candidate to address the performance gap, despite its relatively low Curie temperature $T_C$ of 214 K. In this study, density functional theory was employed to investigate the effect of Si and Co substitution on the magnetic moments, magnetocrystalline anisotropy energy (MAE) and Curie temperature in ${\mathrm{Fe}}_{2-y}$Co_yP_1−xSi_x compounds. Our findings indicate that Si substitution enhances magnetic moments due to the increase in 3f-3f and 3f-3g interaction energies, which also contribute to higher $T_C$ values. Conversely, Co substitution leads to a reduction in magnetic moments, attributable to the inherently lower magnetic moments of Co. In all examined cases of different Si concentrations, such as hexagonally structured ${\mathrm{Fe}}_{2-y}$Co_yP, ${\mathrm{Fe}}_{2-y}$Co_yP_0.92Si_0.08 and ${\mathrm{Fe}}_{2-y}$Co_yP_0.84Si_0.16, Co substitution increases the Curie temperatures by augmenting 3g-3g exchange interaction energies. Both Si and Co substitutions decrease the magnetocrystalline anisotropy energy, resulting in the loss of the easy magnetization direction at higher Co contents. However, higher Si concentrations appear to confer resilience against the loss. In summary, Si and Co substitutions effectively modify the investigated magnetic properties. Nonetheless, to preserve a high MAE, the extent of substitution should be optimized. Full article

Recently, significant effort has been devoted to enhancing magnetic anisotropy energy (MAE) and the Dzyaloshinskii–Moriya interaction (DMI) in two-dimensional (2D) ferromagnetic materials through various tuning approaches. Among these methods, defect engineering is one of the most effective strategies. However, the influence of these charged defects on the MAE and DMI is unclear. Therefore, we systematically investigate the defect effect on the MAE and DMI of I vacancy-doped (v_I-CrI₃), 3d-transition-metal-doped (TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) (3d-TM_i@CrI₃), and v_I-TM co-doped (3d-TM_i@v_I-CrI₃) monolayer CrI₃ using first-principles calculations. Our results indicate that Cr-rich conditions can promote the defect formation of v_I-CrI₃, 3d-TM_i@CrI₃, and 3d-TM_i@v_I-CrI₃ systems and demonstrate that 49 types of charged systems are stable. Among these systems, the Cu_i@v_I-CrI₃ in the +1 charge state (Cu_i^•@v_I-CrI₃) system has a smaller defect formation energy, exhibiting a large MAE exceeding 30 meV, and the ratio (D/J) of the antisymmetric magnetic exchange parameter (D) to the Heisenberg exchange parameter (J) reaches 1.04. The large MAE originates from the transition from single-ion anisotropy (SIA) to covalent interaction anisotropy (CIA) due to the coupling variation between the p_y and p_x orbitals of I atoms near the Fermi level caused by charge states. The enhancement of the DMI is due to the electrostatic potential differences between the I-top and I-bottom layers, which are conducive to forming stable chiral spin textures. This study provides insight into the defect charge state modulating the magnetism of 2D magnetic materials. Full article

By performing first-principles calculations, we predicted a kind of novel ultrathin two-dimensional (2D) ferromagnet, single-atomic-layer EuN. EuN monolayer is a ferromagnetic half-metal with a large band gap of 1.69 eV; Eu ions in EuN are in the highest spin state and have large magnetic moments of 6 μB, much larger compared with the non-rare-earth (RE) metal ions. The magneto-crystalline anisotropy energy (MCE) of EuN monolayer is −3.72 meV per Eu ion, which is much higher than that of CrI₃ monolayer (0.685 meV per Cr ion); the magnetic dipolar energy (MDE) enhances magnetic anisotropy for EuN monolayer; large magnetic anisotropy energy (MAE) is beneficial to stabilizing the long-range ferromagnetic ordering. More importantly, different from many RE metal monolayers, hybridization between Eu-f and N-p orbitals induces ferromagnetism for EuN monolayer; the Curie temperature of EuN monolayer is above the liquid-nitrogen temperature (100 K). Additionally, the Curie temperature of EuN monolayer increases with increasing biaxial strain due to increased f-p hybridization. Full article

The impact of rhenium doping on the transport properties and electron localization in monolayer graphene was experimentally investigated. In this study, we report the emergence of unsaturated negative magnetoresistance in Re-doped graphene devices, which is observed exclusively at low temperatures. Moreover, angle-dependent measurements reveal a pronounced anisotropy in the negative magnetoresistance. This phenomenon is attributed to the disorder and localized magnetic moments introduced by Re doping, which lead to charge carrier localization and are accompanied by substantial magnetocrystalline anisotropy energy. Full article

Two-layered structures consisting of piezopolymer and magnetic elastomer were investigated as magnetoelectric material. Three types of magnetic elastomer based on cobalt ferrite (CoFe₂O₄) and Ni- or Zn-substituted CoFe₂O₄ nanoparticles were used as magnetically sensitive layers. Cobalt ferrite nanoparticles are considered one of the most promising metal-oxide nanomaterials because of their favorable magnetic properties, such as high saturation magnetization and magnetic anisotropy. The substitution of Co²⁺ in cobalt ferrite with other transition metals allows for additional tailoring of these properties. The modified magnetic behavior of the substituted CoFe₂O₄ nanoparticles directly influenced the magnetic properties of magnetic elastomers and, consequently, the magnetoelectric response of composite structures. In this case, the resonant frequency of the magnetoelectric effect remained largely independent of the type of magnetic nanoparticles in the magnetic elastomer layer but its magnitude increased upon Zn substitution up to ~107 mV·cm⁻¹·Oe⁻¹. These findings highlight the potential of chemically engineered magnetic properties of CoFe₂O₄ nanoparticles for manufacturing magnetoelectric composites to expand their applications in energy harvesting and sensors. Full article

In order to meet the demand for high-frequency current sensors in 5G communication and new energy fields, there is an urgent need to develop high-performance nickel-zinc ferrite-based co-fired ceramic magnetic cores. In this study, a nickel-zinc ferrite core based on low temperature co-fired ceramic (LTCC) technology was developed. The regulation mechanism of BaCo_0.06Bi_0.94O₃ doping on the low-temperature sintering characteristics of NiZn ferrites was systematically investigated. The results show that the introduction of BaCo_0.06Bi_0.94O₃ reduces the sintering temperature to 900 °C and significantly improves the density and grain uniformity of ceramics. When the doping amount is 0.75 wt%, the sample exhibits the lowest coercivity of 35.61 Oe and the following optimal soft magnetic properties: initial permeability of 73.74 (at a frequency of 1 MHz) and quality factor of 19.64 (at a frequency of 1 MHz). The highest saturation magnetization reaches 66.07 emu/g at 1 wt% doping. The results show that BaCo_0.06Bi_0.94O₃ doping can regulate the grain boundary liquid phase distribution and modulate the magnetocrystalline anisotropy, which provides an experimental basis and optimization strategy for the application of LTCC technology in high-frequency current sensors. Full article

Fe-based amorphous and nanocrystalline alloys, such as FINEMET and its improved variants, are highly valued as green energy-saving materials due to their unique magnetic properties, including high permeability, low coercivity, and near-zero saturation magnetostriction. These characteristics have enabled their extensive use in power electronics and information technology. However, the full potential of these alloys remains unfulfilled due to insufficient understanding of their stress sensitivity. This study focuses on the development history, heat treatment, annealing processes, chemical composition, and underlying mechanisms of Fe-based amorphous and nanocrystalline alloys, aiming to provide insights into stress-induced magnetic anisotropy and guide the development of greener and more efficient soft magnetic materials. Full article

Ta₂AlC is an emerging ceramic material characterized by its high melting point, high hardness, excellent thermal stability, and superior mechanical properties, which allow for broad application prospects in aerospace and defense fields. This paper investigates the physical mechanisms underlying the modulation of the mechanical and photoelectric properties of Ta₂AlC through doping using the first-principles pseudopotential plane-wave method. We specifically calculated the geometric structure, mechanical properties, electronic structure, Mulliken population analysis, and optical properties of Ta₂AlC doped with V, Ga, or Si. The results indicate that doping induces significant changes in the structural parameters of Ta₂AlC. By applying the Born’s criterion as the standard for mechanical stability, we have calculated that the structures of Ta₂AlC, both before and after doping, are stable. The mechanical property calculations revealed that V and Si doping weaken the material’s resistance to deformation while enhancing its plasticity. In contrast, Ga doping increases the material’s resistance to lateral deformation and brittleness. Doping also increases the anisotropy of Ta₂AlC. Electronic structure calculations confirmed that Ta₂AlC is a conductor with excellent electrical conductivity, which is not diminished by doping. The symmetric distribution of spin-up and spin-down electronic state densities indicates that the Ta₂AlC system remains non-magnetic after doping. The partial density of states diagrams successfully elucidated the influence of dopant atoms on the band structure and electronic state density. Mulliken population analysis revealed that V and Ga doping enhance the covalent interactions between C-Ta and Al-Ta atoms, whereas Si doping weakens these interactions. Optical property calculations showed that V and Si doping significantly enhance the electromagnetic energy storage capacity and dielectric loss of Ta₂AlC, while Ga doping has minimal effect. The reflectivity of doped and undoped Ta₂AlC reaches over 90% in the ultraviolet region, indicating its potential as an anti-ultraviolet coating material. In the visible light region, both doped and undoped Ta₂AlC exhibit a similar metallic gray appearance, suggesting its potential as a temperature control coating material. The light loss of Ta₂AlC is limited to a narrow energy range, indicating that doping does not affect its use as a light storage material. These results demonstrate that different dopants can effectively modulate the mechanical and photoelectric properties of Ta₂AlC. Full article

Magnetic random-access memory, recognized as a breakthrough in spintronics, demonstrates substantial potential for next-generation nonvolatile memory and logic devices due to its unique magnetization-switching mechanism. However, realizing reliable perpendicular magnetization switching via spin–orbit torque necessitates an externally applied in-plane magnetic bias, a requirement that complicates integration in high-density device architectures. This study proposes a novel device architecture where geometric asymmetry engineering in an interlayer design generates an intrinsic equivalent in-plane magnetic field. By strategically introducing a non-symmetrical spacer between the heavy metal and ferromagnetic layers, we establish deterministic magnetization reversal while eliminating external field dependency. Furthermore, the energy barrier during magnetization switching is dynamically adjusted by applying a voltage across a perpendicular-anisotropy magnetic tunnel junction, leveraging the voltage-controlled magnetic anisotropy effect. We established a physics-driven compact model to assess the design and performance of voltage-controlled spin–orbit torque magnetic tunnel junction (VCSOT-MTJ) devices. Simulations reveal that the introduction of a minimally asymmetric light metal layer effectively resolves the issue of incomplete switching in field-free spin-orbit torque systems. Full article

A chain of dipole-coupled elongated magnetic islands whose long axes are oriented perpendicular to the chain is studied for its magnetization properties. With a magnetic field applied perpendicular to the chain, the competition between dipolar energy, shape anisotropy, and field energy leads to three types of uniform states with distinct magnetizations: (1) oblique to the chain, (2) perpendicular to the chain, and (3) zero due to having alternating dipoles. The response of these states to a slowly varying field is analyzed, focusing on their stability limits and related oscillation modes, and the dependencies on the dipolar and anisotropy constants. Based on identifiable transitions among the three states and their instability points, the theoretically predicted zero-temperature magnetization curves show significant dependence on the anisotropy. The model suggests a path for designing advanced materials with desired magnetic properties. Different geometries and magnetic media for the islands are considered. Full article

Four similar dinuclear lanthanide complexes have been synthesized by linking two [Ln(hfac)_2–3] units (hfac stands for hexafluoroacetylacetone) with different μ-O bridging ligands. The 2,2′-bipyridine-N-oxide ligand (bmpo) constructed two centrosymmetric complexes [Ln₂(hfac)₆(bmpo)₂] (Ln = Dy(1), Tb(2)), with nine-coordinated Ln^III ions showing C_s low symmetry, while the ligand di(2-pyridyl)methanediol (py₂C(OH)₂) formed another two compounds [Ln₂(hfac)₄(py₂C(OH)O)₂] (Ln = Dy(3), Tb(4)), with two kinds of eight-coordinated Ln^III ions exhibiting improved symmetries of D_4d and D_2d. Magnetic analysis reveals that Dy₂ complex 1 shows intramolecular antiferromagnetic coupling (J = −1.07 cm⁻¹) and no relaxation process above 2.0 K even in a 1000 Oe dc field, owing to the low symmetry of Dy^III ions, while the similar Dy₂ complex 3 with improved Dy^III symmetry shows ferromagnetic coupling (J = 1.17 cm⁻¹), which induces a 1000 Oe dc field-induced two-step magnetization relaxation processes with effective energy barrier U_eff = 47.4 K and 25.2 K for the slow relaxation and fast relaxation processes, respectively. This study proves again that the improved symmetry combined with intramolecular ferromagnetic interactions, both mediated by bridging ligands, can enhance the Dy^III anisotropy, further quench the quantum tunneling of the magnetization, and finally, enhance the magnetic behavior of Ln^III-based systems. Full article

We study a system of ultra-cold dipolar Bose gas atoms confined in a two-dimensional (2D) harmonic trap with a dipolar impurity implanted at the center of the trap. Due to recent experimental progress in dipolar condensates, we focused on calculating properties of dipolar impurity systems that might guide experimentalists if they choose to study impurities in dipolar gases. We used the Gross–Pitaevskii formalism solved numerically via the split-step Crank–Nicolson method. We chose parameters of the background gas to be consistent with dysprosium (Dy), one of the strongest magnetic dipoles and of current experimental interest, and used chromium (Cr), erbium (Er), terbium (Tb), and Dy for the impurity. The dipole moments were aligned by an external field along what was chosen to be the z-axis, and we studied 2D confinements that were perpendicular or parallel to the external field. We show density contour plots for the two confinements, 1D cross-sections of the densities, calculated self-energies of the impurities while varying both number of atoms in the condensate and the symmetry of the trap. We also calculated the time evolution of the density of an initially pure system where an impurity is introduced. Our results show that while the self-energy increases in magnitude with increasing number of particles, it is reduced when the trap anisotropy follows the natural anisotropy of the gas, i.e., elongated along the z-axis in the case of parallel confinement. This work builds upon work conducted in Bose gases with zero-range interactions and demonstrates some of the features that could be found when exploring dipolar impurities in 2D Bose gases. Full article