Ferrimagnetic Coupling Research Articles

Toroidal Protein Adaptor Assembles Ferrimagnetic Nanoparticle Fibers with Constructive Magnetic Coupling

Inspired by nature, the synthesis of biohybrid nanocomposites containing inorganic nanoparticles (NPs) and biopolymers such as DNA and peptides as templates offers great potential for a wide range of applications. Using selective recognition schemes of 3D protein spaces for the assembly of magnetic nanocrystals is a challenge with great promise in the field of biomedicine and magnetic data storage. Here we apply the toroidal protein Hcp1 as an interparticle connector for the directed molecular assembly and ferrimagnetic coupling of biohybrid cobalt ferrite NP wires. The resulting biohybrid NP composites show bundles of nanofibers ranging from nano‐ to the microscale in length verified by TEM, EDX analysis and focused ion beam cut. Their magnetic characterization reveals an increase of the coercive field (+12%) reaching values of high‐end Nd2Fe14B bulk magnets, enhanced saturation (+28%) and remanence magnetization (+38%) at 2 K compared to NPs lacking the protein connector. Thus, the combination of the nanoscale alignment of magnetic NPs with the molecular precision of the protein connectors leads to constructive addition of the magnetization reversal energy. This approach can be used to control magnetic properties for the design of materials with enhanced coercivity applicable for magnetic data storage, hyperthermia and theranostics.

Magnetic properties of a nanoribbon: An effective-field theory

An effective-field theory is proposed to study magnetic properties of a nanoribbon. The model consists of a core spin-3/2 and shell spin-2 with a ferrimagnetic exchange coupling, which is described by transverse Ising model with the anisotropy. Based on the differential operator technique, the magnetization and the susceptibility formulas of the nanoribbon are given. Numerical results of the magnetization, the susceptibility, the hysteresis loop of the system are discussed for specific values of the parameters. Magnetization plateaus exhibits on the magnetization curves at low temperature. The exchange coupling, the anisotropy and the transverse field have important roles in the magnetic properties for the nanoribbon. Results may provide some guidance to design in the nanoribbons.

Spin-Related Micro-Photoluminescence in Fe3+ Doped ZnSe Nanoribbons

Spin-related emission properties have important applications in the future information technology; however, they involve microscopic ferromagnetic coupling, antiferromagnetic or ferrimagnetic coupling between transition metal ions and excitons, or d state coupling with phonons is not well understood in these diluted magnetic semiconductors (DMS). Fe3+ doped ZnSe nanoribbons, as a DMS example, have been successfully prepared by a thermal evaporation method. Their power-dependent micro-photoluminescence (PL) spectra and temperature-dependent PL spectra of a single ZnSe:Fe nanoribbon have been obtained and demonstrated that alio-valence ion doping diminishes the exciton magnetic polaron (EMP) effect by introducing exceeded charges. The d-d transition emission peaks of Fe3+ assigned to the 4T2 (G) → 6A1 (S) transition at 553 nm and 4T1 (G) → 6A1 (S) transition at 630 nm in the ZnSe lattice have been observed. The emission lifetimes and their temperature dependences have been obtained, which reflected different spin–phonon interactions. There exists a sharp decrease of PL lifetime at about 60 K, which hints at a magnetic phase transition. These spin–spin and spin–phonon interaction related PL phenomena are applicable in the future spin-related photonic nanodevices.

Phase diagrams and magnetic properties of ferrimagnetic mixed spin-12 and spin-32 Ising nanowire

A hexagonal nanowire consisting of a ferromagnetic spin–12 core and spin–32 outer shell coupled with ferrimagnetic interlayer coupling has been studied by the use of the Monte Carlo simulation based on the heat bath algorithm. Particular emphasis is given to the effects of the size, the crystal field, the shell and the interface coupling constants on the critical and the compensation phenomenon. Some interesting behaviors have been observed which include the first and second order phase transitions. The isolated critical points are also observed. We have also found that the system exhibits the compensation phenomenon for appropriate values of the system parameters. The critical exponent has also been calculated.

Magnetic properties of a hexagonal prismatic nanoparticle with ferrimagnetic core–shell structure

Based on Monte Carlo simulation a hexagonal prismatic nanoparticle consisting of a ferromagnetic core of spin-1 surrounded by a ferromagnetic shell of spin-3/2 with ferrimagnetic interface exchange coupling has been investigated. Curves of magnetizations, magnetic susceptibilities, internal energy of the system and phase diagrams are obtained and discussed in detail. It has shown that exchange couplings and single-ion anisotropies of core and shell sublattice play important roles in magnetic properties of the system. A number of characteristic types of magnetization curves have been plotted. The occupation of shell sublattice by spin-3/2 results in the different initial values of total magnetization. The internal energy of the system shows a different variation when different parameters change. For the appropriate parameters, the nanoparticle may exhibit compensation behavior. Especially, two compensation temperatures have been found in this system.

Electronic structures and magnetic properties in Cu-doped two-dimensional dichalcogenides

We explore the electronic structures and magnetic properties in Cu-doped MX2 (=MoS2, MoSe2, MoTe2, and WS2) based on density functional theory. A Cu dopant leads to a net moment of 5.0 or 1.0μB in MX2, which mainly depend on the size of crystal-field splitting relative to that of the spin splitting. No magnetism is observed in Cu-doped MoTe2. The local distortion around the Cu atom reduces the total magnetic moment in two-Cu-doped MX2. The magnetic coupling between the nearest neighboring Cu atoms is ferromagnetic for all the cases, but they demonstrate various magnetic ground states with the increasing distance between Cu atoms: the Cu-doped MoS2 and WS2 exhibit anti-ferromagnetic and nonmagnetic ground state, respectively. A long-range ferromagnetic or ferrimagnetic coupling is attributed to double-exchange interaction in Cu-doped MoSe2. Half-metallic ferromagnetism with Curie temperature above room temperature in Cu-doped MoSe2 provides a useful guidance to engineer the magnetic properties of MoSe2 in experiments.

Structure and magnetism of Sr3NiSb2O9

The crystal structure of the perovskite-related oxide Sr3NiSb2O9 has been refined from X-ray and neutron powder diffraction data; space group P21/n, a=5.64381(2), b=5.62299(2), c=7.95687(3)Å, β=90.014(2)°. The structure has two crystallographically-distinct six-coordinate cation sites with occupancies Sb 0.97(1), Ni 0.03 and Sb 0.36, Ni 0.64. The magnetic susceptibility has been measured over the temperature range 2≤T/K≤300. Fitting data recorded in the temperature range 150<T/K<300 to the Curie–Weiss law resulted in µeff=3.49(1)µB per Ni2+, θ=−138(1)K. Ferrimagnetic coupling in the vicinity of the antisite defects is suggested to be responsible for the enhanced susceptibility observed below ~90K. The zero-field cooled susceptibility shows a maximum at 8.7K that is not observed in the field-cooled susceptibility. Hysteresis is observed in M(H) at 2K but not at 7.5K.

Synthesis, Magnetic Properties, and X‐ray Spectroscopy of Divalent Cobalt(II) and Nickel(II) Cubanes [MII4(HL2)4(OAc)4

AbstractUnder anaerobic conditions, the reactions of cobalt(II) and nickel(II) acetate tetrahydrate with 2,6‐pyridinedimethanol (H2L2, 3) in anhydrous acetonitrile afforded two tetranuclear metal(II) complexes [MII4(HL2)4(OAc)4] (4; MII = Co2+, Ni2+) with a [M4(μ3‐O)4]4+ cubane core. X‐ray structural analyses revealed that both MII cubanes 4a·2CH3OH and 4b·2CH3OH are isostructural and crystallize in the tetragonal space group I41/acd with eight molecules in the unit cell. In the solid state, the orientation of the cubane cores of 4 and the formation of a 3D framework were controlled by π–π interactions as well as intra‐ and intermolecular O–H···O hydrogen bonds. Variable‐temperature magnetic susceptibility measurements revealed that the cubanes 4 show a ferrimagnetic coupling scheme that leads to a diamagnetic ground state for both complexes. Core‐level X‐ray photoelectron spectroscopy confirmed that the Co and Ni ions in 4a and 4b are in a divalent state. X‐ray magnetic circular dichroism was performed to extract the spin and orbital contributions to the Co and Ni magnetic moments. We compared the experimental results of the local electronic structures around the Co2+ ions in 4a and the Ni2+ ions in 4b with charge‐transfer multiplet simulations.

Ferrimagnetic behaviors in a double-wall cubic metal nanotube

A double-wall cubic metal nanotube consists of the ferromagnetic spin-1 inner shell and spin-3/2 surface shell. It is of the ferrimagnetic exchange coupling between two shells. Considering the single-ion anisotropy and transverse field exist together, the magnetization, the initial susceptibility, the internal energy and the specific heat have been investigated by using the effective-field theory with correlations. Some interesting phenomena have been found in the thermal variations of the system. Magnetization appears two or three compensation points in certain parameters. It is an unconventional ferrimagnetic behavior in the nanotube. The shapes of total magnetization and the initial susceptibility are great influenced by the surface exchange coupling, surface single-ion anisotropy and surface transverse field. Some results of nanotube may have potential applications in different research fields, such as electronics, optics, mechanics, and even biomedicine and molecular devices.

Magnetic properties of a single transverse Ising ferrimagnetic nanoparticle

Using the effective field theory with a probability distribution technique that accounts for the self-spin correlation function, the thermal and the magnetic properties of a single Ising nanoparticle consisting of a ferromagnetic core, a ferromagnetic surface shell and a ferrimagnetic interface coupling are examined. The effect of the transverse field in the surface shell, the exchange interactions between core/shell and in surface shell on the free energy, thermal magnetization, specific heat and susceptibility are studied. A number of interesting phenomena have been found such as the existence of the compensation phenomenon and the magnetization profiles exhibit P-type, N-type and Q-type behaviors.

Magnetic Moment Enhancement for Mn7 Cluster on Graphene

Mn7 cluster on graphene with different structural motifs and magnetic orders are investigated systematically by first-principles calculations. The calculations show that Mn7 on graphene prefers a two-layer motif and exhibits a ferrimagnetic coupling. The magnetic moment of the Mn7 cluster increases from 5.0 μB at its free-standing state to about 6.0 μB upon adsorption on graphene. Mn7 cluster also induces about 0.3 μB of magnetic moment in the graphene layer, leading to an overall enhancement of 1.3 μB magnetic moment for Mn7 on graphene. Detail electron transfer and bonding analysis have been carried out to investigate the origin of the magnetic enhancement.

Insulator-half metal transition driven by hole doping: a density functional study of Sr-doped La2VMnO6.

La2VMnO6 is an insulating ferrimagnet experimentally. By substituting La with Sr, La2-xSrxVMnO6 (x = 0.5, 1.0, 1.5, 2.0) was investigated using the density functional theory. Our results indicated that half metallic properties are obtained for x = 0.5, 1.5, 2.0. For x = 1.0, it is insulating. With the increase of hole doping, the holes initially go to V 3d orbitals for x = 0.5, 1.0, and after that, the holes go to the Mn 3d orbitals for x = 1.5, 2.0. Ferrimagnetic coupling between V and Mn is found to be the ground state for x = 0.5, 1.5, while for x = 1.0 and 2.0, ferromagnetic and antiferromagnetic couplings between Mn and Mn are competitive for the ground state.

Magnetic properties and thermodynamics in a metallic nanotube

A metallic nanotube composed of the ferromagnetic spin-3/2 inner shell and spin-1 outer shell with a ferrimagnetic interlayer coupling has been studied by using the effective-field theory with correlations (EFT). With both existence of the magnetic anisotropy and transverse field, we have studied effects of them on the magnetic properties and the thermodynamics. Some interesting phenomena have been found in the phase diagrams. At low temperature, the magnetization curves present different behaviors. Two compensation points have been found for the certain values of the system parameters in the system. The research results of metallic nanotubes may have potential applications in the fields of biomedicine and molecular devices.

Hysteresis loop of a cubic nanowire in the presence of the crystal field and the transverse field

The effective-field theory with correlations (EFT) has been used to study the various shapes of the hysteresis loop for a ferromagnetic core of spin-1 and a ferromagnetic shell of spin-3/2 with ferrimagnetic interface coupling on a cubic nanowire. The magnetizations and phase diagrams of the nanowire have been investigated in the previous work (J. Magn. Magn. Mater. 324 (2012) 4034–4042). A number of characteristic behaviors are obtained especially for the triple and multiple hysteresis loop patterns for certain values of the system parameters at low temperature. We also examine the effect of the system parameters on coercivity of the nanowire.

Atomic-scale structure and electronic property of the La2FeCrO6/SrTiO3 interface

Combining transmission electron microscopy with first-principles calculations, we investigate atomic-scale structure of a La2FeCrO6/SrTiO3 interface and related it to its electronic properties at the atomic scale with special focus on the strain effect. We find that the La2FeCrO6 film shows a clean and direct contact to the substrate and that an epitaxial, coherent and atomically sharp interface is formed between La2FeCrO6 and SrTiO3. By estimating the adhesion energies for 21 possible candidate interface geometries, we determine the most stable interface structure theoretically, in consistence with the experimental data. The strain is found to play an insignificant role in affecting interfacial atomic structures, yet impose a substantial electronic impact. The strain induces interfacial electronic states and is responsible for the covalent nature of the interfacial bonding. Moreover, the valence states of Fe and Cr are identified to be +3, and a ferrimagnetic coupling is revealed between Fe and Cr.

Morphology, Microstructure, and Magnetic Properties of Ordered Large-Pore Mesoporous Cadmium Ferrite Thin Film Spin Glasses

Herein, we report the synthesis, microstructure, and magnetic properties of cadmium ferrite (CdFe2O4) thin films with both an ordered cubic network of 18 nm diameter pores and single-phase spinel grains averaging 13 nm in diameter. These mesoporous materials were produced through facile polymer templating of hydrated nitrate salt precursors. Both the morphology and the microstructure, including cation site occupancy and electronic bonding configuration, were analyzed in detail by electron microscopy, grazing incidence small-angle X-ray scattering, Raman and X-ray photoelectron spectroscopy, and N2-physisorption. The obtained data demonstrate that the network of pores is retained up to annealing temperatures as high as 650 °C--the onset of crystallization is at ϑ = (590 ± 10) °C. Furthermore, they show that the polymer-templated samples exhibit a "partially" inverted spinel structure with inversion parameter λ = 0.40 ± 0.02. This differs from microcrystalline CdFe2O4 which shows virtually no inversion. Magnetic susceptibility studies reveal ferrimagnetic spin coupling below 147 K and further point to the likelihood of glassy behavior at low temperature (T(f) ≈ 60 K). In addition, analysis of room temperature magnetization data indicates the presence of sub-10 nm diameter superparamagnetic clusters in an otherwise paramagnetic environment.

From (3,6)-Connected kgd, chiral anh to (3,8)-connected tfz-d Nets in Low Nuclear Metal Cluster-Based Networks with Triangular Pyridinedicarboxylate Ligand

Four novel coordination polymers based on asymmetric triangular 5-(4′-carboxylphenyl) nicotinic acid (H2cpna), namely, Ni(cpna)(H2O)2 (1), M2(cpna)2(H2O)3·0.5H2O·DMF [M = Ni for (2), Co for (3)] and Ni3(Hcpna)2(cpna)2(H2O)4·2H2O (4), have been synthesized under solvothermal conditions. All of the four compounds contain low nuclear metal clusters as secondary building units (SBUs). Complex 1 exhibits two-dimensional (3,6)-connected (43)2(46.66.83)-kgd topology, in which cpna ligands and edge-shared dinuclear SBUs act as 3-connected and 6-connected nodes, respectively. Compounds 2 and 3 are constructed by corner-shared dinuclear SBUs and show an unprecedented (3,6)-connected chiral (42.6)2(44.62.88.10)-anh (flu-3, P6222) topology. In 4, linear trimers are ligated by six cpna ligands to form a planar (43)2(46.66.83)-kgd layer, and adjacent layers are further linked by Hcpna– ligands through Ni–O and Ni–N bonds to form three-dimensional (3,8)-connected (43)2(46.618.84)-tfz-d net. Both 1 and 4 crystallize in the triclinic crystal system with symmetric space group P̅1, which result in an equal ratio of (R)- and (S)-cpna isomers. Isostructural 2 and 3 crystallize in a trigonal crystal system with the chiral space group P3221, and a single crystal contains a sole optical isomer of cpna, although bulk crystals are a racemic mixture. Variable-temperature magnetic susceptibility measurements reveal ferromagnetic coupling of edge-shared dimers in 1, antiferromagnetic coupling of corner-shared dimers in 2 and 3, and ferrimagnetic coupling of linear trimers in 4.

Magnetocaloric effect in M–pyrazole–[Nb(CN)8] (M = Ni, Mn) molecular compounds

We report a study of magnetocaloric effect (MCE) in cyanido-bridged {[MII(pyrazole)4]2[NbIV(CN)8]⋅4H2O}n molecular compounds where M = Ni, Mn, pyrazole = C3H4N2. The substances show a sharp phase transition to a long range magnetically ordered state, with ferromagnetic coupling between M and Nb sublattices in the case of the Ni-based sample 1 (Tc = 13.4 K) and ferrimagnetic coupling for the Mn-based sample 2 (Tc = 23.8 K). The magnetic entropy change ΔS due to applied field change ΔH as a function of temperature was determined by the magnetization and heat capacity measurements. The maximum value of ΔS at μ0ΔH = 5 T is 6.1 J mol−1 K−1 (5.9 J kg−1 K−1) for 1 at T = 14 K and 6.7 J mol−1 K−1 (6.5 J kg−1 K−1) for 2 at T = 25 K. MCE data at different applied fields have been presented as one universal curve, which confirms magnetic transitions in 1 and 2 to be of second order. The temperature dependences of the n exponent characterizing the dependence of ΔS on ΔH have been obtained. The n(Tc) values, consistent with the shape of the magnetization curves, pointed to the 3D Heisenberg behaviour for 2 and some anisotropy, probably of the XY type, for 1. The (H/Tc)2/3 dependence of the maximum entropy change has been tested in the ferrimagnetic Mn2–L–[Nb(CN)8] (L = C3H4N2, C4H4N2) series.

Surface effects on a ferrimagnetic hexagonal nanowire with single-ion anisotropis and transverse field

A hexagonal nanowire consists of the ferromagnetic spin-3/2 core and spin-1 outer shell coupled with ferrimagnetic interlayer coupling has been studied. The general formula for the temperature dependence of the longitudinal and the transverse magnetization of the system is given. Particularly, emphases of the effects of the physical parameters on transition temperature and the range of physical parameters over which two compensation points exist are given. The competition among the exchange coupling between the outer shell and core, the outer shell coupling, the anisotropies, the transverse field, and the temperature has a profound effect on the characteristic of magnetic properties in the hexagonal nanowire system.

Environmental Influence on the Single-Molecule Magnet Behavior of [MnIII6CrIII]3+: Molecular Symmetry versus Solid-State Effects

The structural, spectroscopic, and magnetic properties of a series of [Mn(III)(6)Cr(III)](3+) (= [{(talen(t-Bu(2)))Mn(III)(3)}(2){Cr(III)(CN)(6)}](3+)) compounds have been investigated by single-crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and electronic absorption spectroscopy, elemental analysis, electro spray ionization-mass spectrometry (ESI-MS) and matrix-assisted laser desorption ionization-mass spectrometry (MALDI-MS), cyclic voltammetry, AC and DC magnetic measurements, as well as theoretical analysis. The crystal structures obtained with [Cr(III)(CN)(6)](3-) as a counterion exhibit (quasi-)one-dimensional (1D) chains formed by hydrogen-bonded (1) or covalently linked (2) trications and trianions. The rod-shaped anion lactate enforces a rod packing of the [Mn(III)(6)Cr(III)](3+) complexes in the highly symmetric space group R3[overline] (3) with a collinear arrangement of the molecular S(6) axes. Incorporation of the spherical anion BPh(4)(-) leads to less-symmetric crystal structures (4-6) with noncollinear orientations of the [Mn(III)(6)Cr(III)](3+) complexes, as evidenced by the angle between the approximate molecular C(3) axes taking no specific values in the range of 2°-69°. AC magnetic measurements on freshly isolated crystals (1a and 3a-6a), air-dried crystals (3b-6b), and vacuum-dried powder samples (3c-6c) indicate single-molecule magnet (SMM) behavior for all samples with U(eff) values up to 28 K. The DC magnetic data are analyzed by a full-matrix diagonalization of the appropriate spin-Hamiltonian including isotropic exchange, zero-field splitting, and Zeeman interaction, taking into account the relative orientation of the D-tensors. Simulations for 3a-6a and 3c-6c indicate a weak antiferromagnetic exchange between the Mn(III) ions in the trinuclear subunits (J(Mn-Mn) = -0.70 to -0.85 cm(-1), Ĥ(ex) = -2∑(i<j )J(ij)Ŝ(i)·Ŝ(j)) that is overcome by the stronger antiferromagnetic interaction via the Cr-C≡N-Mn pathway (J(Cr-Mn) = -3.00 to -5.00 cm(-1)), leading to an overall ferrimagnetic coupling scheme with an S(t) = (21)/(2) spin ground state. The differences in U(eff), J(Mn-Mn), and J(Cr-Mn) for the investigated samples are rationalized in terms of subtle variations in the molecular and crystal structures. In particular, a magnetostructural correlation between the Mn-N(C≡N) bond length and the J(Cr-Mn) exchange coupling is inferred from the magnetic measurements and corroborated by DFT calculations. The results of this detailed study on [Mn(III)(6)Cr(III)](3+) allow the formulation of some key recipes for a rational improvement of the SMM behavior.