Magnetochemistry, Volume 7, Issue 8 (August 2021) – 14 articles

We investigate maneuvering superparamagnetic microparticles, or beads, in a remotely-controlled, automated way across arrays of few-micron-diameter permalloy disks. This technique is potentially useful for applying tunable forces to or for sorting biological structures that can be attached to magnetic beads, for example nucleic acids, proteins, or cells. The particle manipulation method being investigated relies on a combination of stray fields emanating from permalloy disks as well as time-varying externally applied magnetic fields. Unlike previous work, we closely examine particle motion during a capture, rotate, and controlled repulsion mechanism for particle transport. We measure particle velocities during short-range motion—the controlled repulsion of a bead from one disk toward another—and compare this motion to a simulation based on stray fields from disk edges. We also observe the phase-slipping and phase-locked motion of particles engaging in long-range transport in this manipulation scheme. Full article

Single layer low-dimensional materials are presently of emerging interest, including in the context of magnetism. In the present report, on-surface supramolecular architecturing was further developed and employed to create surface supported two-dimensional binary spin arrays on atomically clean non-magnetic Au(111). By chemical programming of the modules, different checkerboards were produced combining phthalocyanines containing metals of different oxidation and spin states, diamagnetic zinc, and a metal-free ‘spacer’. In an in-depth, spectro-microscopy and theoretical account, we correlate the structure and the magnetic properties of these tunable systems and discuss the emergence of 2D Kondo magnetism from the spin-bearing components and via the physico-chemical bonding to the underlying substrate. The contributions of the individual elements, as well as the role of the electronic surface state in the bottom substrate, are discussed, also looking towards further in-depth investigations. Full article

We have studied the densification, phase formation, microstructure, and permeability of stoichiometric and Fe-deficient Ni-Cu-Zn ferrites of composition Ni_0.30Cu_0.20Zn_0.50+zFe_2-zO_4-(z/2) with 0 ≤ z ≤ 0.06 sintered at temperatures from 900 °C to 1150 °C. The shrinkage is shifted from 1000 °C for z = 0 towards lower temperatures and reaches its maximum rate at 900 °C for z = 0.02. Stoichiometric ferrites show regular growth of single-phase ferrite grains if sintered at T_s ≤ 1100 °C. Sintering at 1150 °C leads to the formation of a small amount of Cu₂O, triggering exaggerated grain growth. Fe-deficient compositions (z > 0) form Cu-poor stoichiometric ferrites coexisting with a minority CuO phase after sintering at 900–1000 °C. At T_s ≥ 1050 °C, CuO transforms into Cu₂O, and exaggerated grain growth is observed. The formation of Cu oxide second phases is investigated using XRD, SEM, and EDX. The permeability of the ferrites increases with sintering temperature up to a maximum permeability of µ = 230 for z = 0 or µ = 580 for z = 0.02, respectively, at T_s = 1000 °C. At higher sintering temperatures, the permeability decreases, which is due to the formation of a microstructure with intra-crystalline porosity in large grains, and a non-magnetic Cu oxide grain boundary phase. Full article

Magnetic molecules are prototypical systems to investigate peculiar quantum mechanical phenomena. As such, simulating their static and dynamical behavior is intrinsically difficult for a classical computer, due to the exponential increase of required resources with the system size. Quantum computers solve this issue by providing an inherently quantum platform, suited to describe these magnetic systems. Here, we show that both the ground state properties and the spin dynamics of magnetic molecules can be simulated on prototype quantum computers, based on superconducting qubits. In particular, we study small-size anti-ferromagnetic spin chains and rings, which are ideal test-beds for these pioneering devices. We use the variational quantum eigensolver algorithm to determine the ground state wave-function with targeted ansatzes fulfilling the spin symmetries of the investigated models. The coherent spin dynamics are simulated by computing dynamical correlation functions, an essential ingredient to extract many experimentally accessible properties, such as the inelastic neutron cross-section. Full article

There is significant interest worldwide to identify new antiferromagnetic materials suitable for device applications. Key requirements for such materials are: relatively high magnetocrystalline anisotropy constant, low cost, high corrosion resistance and the ability to induce a large exchange bias, i.e., loop shift, when grown adjacent to a ferromagnetic layer. In this article, a review of recent developments on the novel antiferromagnetic material MnN is presented. This material shows potential as a replacement for the commonly used antiferromagnet of choice, i.e., IrMn. Although the results so far look promising, further work is required for the optimization of this material. Full article

The Magnetospirillum magneticum AMB-1 species is one of the most widely used magnetotactic bacterial strains for producing magnetosomes under laboratory conditions. Nevertheless, there exist several challenges in expanding and purifying the AMB-1 culture due to the restricted culture conditions. In an attempt to enrich the production of magnetosomes, this study reports the utilization of fermenter culture, which substantially promotes the cell densities at different concentrations of iron content. The experimental results confirmed magnetosomes’ high yield (production rate of 21.1 mg L⁻¹) at the iron content of 0.2 μmol L⁻¹. Moreover, different characterization techniques systematically confirmed the coated lipid membrane, particle size, dispersity, stability, and elemental composition of magnetosomes. Notably, the fermenter culture-based process resulted in highly discrete, dispersed, and stable magnetosomes with an average particle diameter of 50 nm and presented the integrated lipid membrane around the surface. The chemical composition by EDS of magnetosomes represented the presence of various elements, i.e., C, O, Na, P, and Fe, at appropriate proportions. In conclusion, the culture method in our study effectively provides a promising approach towards the culture of the magnetotactic bacterium for the enriched production of magnetosomes. Full article

We used a spray-coating process to cover silicon microcantilevers with ca. 33 wt% [Fe(Htrz)₂(trz)](BF₄)@P(VDF₇₀-TrFE₃₀) nanocomposite thin films of 1500 nm thickness. The bilayer cantilevers were then used to investigate the thermomechanical properties of the composites through a combined static and dynamic flexural analysis. The out-of-plane flexural resonance frequencies were used to assess the Young’s modulus of the spray-coated films (3.2 GPa). Then, the quasi-static flexural bending data allowed us to extract the actuation strain (1.3%) and an actuation stress (7.7 MPa) associated with the spin transition in the composite. Full article

Magnetic induction communication and wireless power transmission based on magnetic coupling have significant application prospects in underwater environments. Mutual impedance is a key parameter particularly required for the design of the systems. However, mutual impedance is usually extracted from measurements when the coils are processed, which is obviously not conducive to the system optimization in the design phase. In this paper, a model of the mutual impedance of coils immersed in water is established. The magnetic vector potential is expressed in the form of series by artificially setting a boundary, and then the mutual impedance calculation formula of the coils immersed in water is derived. In the analysis, the effect of the conductivity of water, the excitation frequency, and the number of turns of the coils are mainly taken into account. In addition, the variation of the mutual impedance of coils in air and water with axial displacement is also compared. The models can be used to analyze the coil coupling characteristics in the presence of conductive medium, which is helpful for the design process. Full article

Infections caused by pathogenic bacteria, especially multidrug-resistant bacteria, have become a serious worldwide public health problem. Early diagnosis and treatment can effectively prevent the adverse effects of such infections. Therefore, there is an urgent need to develop effective methods for the early detection, prevention, and treatment of diseases that are caused by bacterial infections. So far, magnetic material nanoparticles (MNPs) have been widely used in the detection and treatment of bacterial infections as detection agents and therapeutics. Therefore, this review describes the recent research on MNPs in bacterial detection and treatment. Finally, a brief discussion of challenges and perspectives in this field is provided, which is expected to guide the further development of MNPs for bacterial detection and treatment. Full article

Despite several decades of active experimental and theoretical studies of rare-earth orthoferrites, the mechanism of the formation of their specific magnetic, magnetoelastic, optical, and magneto-optical properties remains a subject of discussion. This paper provides an overview of simple theoretical model approaches to quantitatively describing the structure–property relationships—in particular, the interplay between FeO₆ octahedral deformations/rotations and the main magnetic and optic characteristics, such as Néel temperature, overt and hidden canting of magnetic sublattices, magnetic and magnetoelastic anisotropy, and optic and photoelastic anisotropy. Full article

The syntheses of new BEDT-TTF derivatives are described. These comprise BEDT-TTF with one ethynyl group (HC≡C-), with two (n-heptyl) or four (n-butyl) alkyl side chains, with two trans acetal (-CH(OMe)₂) groups, with two trans aminomethyl (-CH₂NH₂) groups, and with an iminodiacetate (-CH₂N(CH₂CO₂⁻)₂ side chain. Three transition metal salts have been prepared from the latter donor, and their magnetic properties are reported. Three tris-donor systems are reported bearing three BEDT-TTF derivatives with ester links to a core derived from benzene-1,3,5-tricarboxylic acid. The stereochemistry and molecular structure of the donors are discussed. X-ray crystal structures of two BEDT-TTF donors are reported: one with two CH(OMe)₂ groups and with one a -CH₂N(CH₂CO₂Me)₂ side chain. Full article

Multifunctional molecular materials have attracted material scientists for several years as they are promising materials for the future generation of electronic devices. Careful selection of their molecular building blocks allows for the combination and/or even interplay of different physical properties in the same crystal lattice. Incorporation of redox activity in these networks is one of the most appealing and recent synthetic strategies used to enhance magnetic and/or conducting and/or optical properties. Quinone derivatives are excellent redox-active linkers, widely used for various applications such as electrode materials, flow batteries, pseudo-capacitors, etc. Quinones undergo a reversible two-electron redox reaction to form hydroquinone dianions via intermediate semiquinone radical formation. Moreover, the possibility to functionalize the six-membered ring of the quinone by various substituents/functional groups make them excellent molecular building blocks for the construction of multifunctional tunable metal-organic frameworks (MOFs). An overview of the recent advances on benzoquinone-based MOFs, with a particular focus on key examples where magnetic and/or conducting properties are tuned/switched, even simultaneously, by playing with redox activity, is herein envisioned. Full article

We performed a quantum mechanical study of segregation of Cu atoms toward antiphase boundaries (APBs) in Fe${}_3$Al. The computed concentration of Cu atoms was 3.125 at %. The APBs have been characterized by a shift of the lattice along the ⟨001⟩ crystallographic direction. The APB energy turns out to be lower for Cu atoms located directly at the APB interfaces and we found that it is equal to 84 mJ/m${}^2$. Both Cu atoms (as point defects) and APBs (as extended defects) have their specific impact on local magnetic moments of Fe atoms (mostly reduction of the magnitude). Their combined impact was found to be not just a simple sum of the effects of each of the defect types. The Cu atoms are predicted to segregate toward the studied APBs, but the related energy gain is very small and amounts to only 4 meV per Cu atom. We have also performed phonon calculations and found all studied states with different atomic configurations mechanically stable without any soft phonon modes. The band gap in phonon frequencies of Fe${}_3$Al is barely affected by Cu substituents but reduced by APBs. The phonon contributions to segregation-related energy changes are significant, ranging from a decrease by 16% at T = 0 K to an increase by 17% at T = 400 K (changes with respect to the segregation-related energy difference between static lattices). Importantly, we have also examined the differences in the phonon entropy and phonon energy induced by the Cu segregation and showed their strongly nonlinear trends. Full article

Theoretical calculation plays an important role in the emerging field of single-molecule magnets (SMMs). It can not only explain experimental phenomena but also provide synthetic guidance. This review focuses on discussing the computational methods that have been used in this field in recent years. The most common and effective method is the complete active space self-consistent field (CASSCF) approach, which predicts mononuclear SMM property very well. For bi- and multi-nuclear SMMs, magnetic exchange needs to be considered, and the exchange coupling constants can be obtained by Monte Carlo (MC) simulation, ab initio calculation via the POLY_ANISO program and density functional theory combined with a broken-symmetry (DFT-BS) approach. Further application for these calculation methods to design high performance SMMs is also discussed. Full article