Orientational ordering of protein particles with asymmetric introductions of ferritin in a magnetic field

The mechanism of orientational ordering of protein particles in an inhomogeneous magnetic field, proposed by the authors in Phys. Wave Phenom. 13(1), 1 (2005), was extended to ferritin inclusions in such particles, taking into account the probable appearance of superantiferromagnetic susceptibility properties. Degrees of orientational ordering, ordered state formation and decay times achievable in bioparticle suspensions were estimated for a realistic model of the resistance to motion of elliptic particles in a viscous fluid. Biotechnological applications of the effect are discussed.     

Polarization and transmission of microwaves in the magnetic suspension in the applied magnetic field

The production method of magnetic suspension consisting of ferromagnetic particles dispersed in cedarwood oil is presented at the beginning of this article. Next, the set-up for microwaves generation using a klystron is described. The main part of this paper concerning microwave transmission and polarization during its passage in samples of the produced magnetic suspension placed in a magnetic field is based on the following parameters: induction of this field, filling factor of magnetic suspension by ferromagnetic particles, dimensions of particles, viscosity of liquid carrier, and ratio of the magnetic field changes. Conducted investigations show that microwaves are damped and polarized in these magnetic suspensions. Obtained results are discussed and observed effects are explained by ordering of ferromagnetic particles in magnetic suspension by applied magnetic field.     

Magnetic properties of 3<Emphasis Type="Italic">d</Emphasis>-metal nanocrystalline films

The problem of designing high-resistivity soft magnetic materials based on 3d-metal nanocrystal-line films is discussed. To increase the electrical resistivity, nanogranular composites are proposed; they consist of superparamagnetic particles embedded into a dielectric matrix. To obtain the required soft magnetic properties in such composites, it is necessary to realize magnetic ordering due to the effects of magnetic interaction between nanoparticles. As an example, magnetic films that exhibit good high-frequency properties in a range up to several hundreds of megahertz are presented.     

Lamellar-like structures in ferrofluids placed in strong magnetic fields

We consider a ferrofluid system consisting of magnetic particles interacting with a magnetic dipole–dipole interaction. We study the strong magnetic field regime where all magnetic dipoles are completely polarized in the direction of the magnetic field. We introduce a lattice gas model that serves to describe space ordering phenomena in such systems. It is found that, within mean field theory, this model predicts a second order phase transition to a phase with inhomogeneous lamellar-like ordering below a certain critical temperature.     

Mössbauer effect in small particles

Mössbauer spectroscopy is very sensitive to the special magnetic properties of ultrafine particles. Studies of particles in the superparamagnetic state allow determination of the particle size and the magnetic anisotropy energy constant A strong magnetic interaction between the particles may result in ordering of the magnetic moments of particles which would be superparamagnetic if they were non-interacting. This so-called superferromagnetic state can also be characterized by Mössbauer spectroscopy measurements. Furthermore, because a large fraction of the atoms in very small particles are in the surface layer, Mössbauer spectroscopy can be applied for studies of surface magnetism in small particles.     

Tricritical phenomena in ferronematic liquid crystals

Orientational transitions induced by an external magnetic field in a ferronematic (a suspension of single-domain magnetic particles in a nematic liquid crystal) are considered in the framework of the continuum theory. The surface potential of the interaction between the ferronematic and the bounding plates is used taking into account the fourth-order anisotropy (the modified Rapini potential). It is shown that the ferronematic can be in one of three phases that correspond to three types of orientational ordering: homogeneous ordering, inhomogeneous ordering, and saturation state. The influence of the segregation effect of magnetic particles on the nature of orientational transitions of the ferronematic in an external field is studied. It is established that the transitions between these phases can be of the first and second order depending on the values of the anchoring parameters and the segregation parameter. Tricritical values of the parameter of anchoring anisotropy and the segregation parameter are determined.     

Melting of mesoscopic lattices of magnetic fluid thin film subjected to perpendicular fields

Applying a magnetic field on the magnetic fluid thin film perpendicularly, leads a phase separation that is concentrated in particles separating from a dilute phase. The concentrated phase forms cylindrical columns that construct two-dimensional lattices. This kind of artificial lattice is a novel mesoscopic system and has been explored with optical microscope, CCD, and digital imaging analysis. We explore the ordering evolution of the two-dimensional extraordinary lattice by varying the applied field. The ordering of these lattices is analyzed in terms of translational and bond-orientation correlation functions to address the two-dimensional melting.     

Correlations of two-dimensional super-paramagnetic colloids in tilted external magnetic fields

We outline the formalism of liquid integral equation theory for anisotropic interactions in two dimensions and subsequently apply this theory to one-component super-paramagnetic particles exposed to a tilted magnetic field. Inhomogeneous local ordering of the particles is observed for different in-plane directions. The anisotropy of the interaction as well as of the liquid structure is increased by increasing the tilt angle. Furthermore, the particles favour an alignment in the direction of the in-plane component of the magnetic field. For increasing tilt angle, the anisotropy of the structural correlations is qualitatively similar to that of the corresponding solid lattice which is stable at lower temperatures. However, the mean-square displacements behave qualitatively different in the solid and fluid phases as a function of the tilt angle.     

A model of the properties of colloidal dispersions of weakly interacting fine ferromagnetic particles

A Monte Carlo technique has been used to simulate the magnetic properties of a colloidal dispersion of weakly interacting fine ferromagnetic particles. The initial susceptibility is shown to obey a Curie-Weiss like law in its variation with temperature. The ordering temperature in the Curie-Weiss law is found to increase with the diameter of the particles, the increase being associated with an increase in the local order in the system. Data from the Monte Carlo simulation is also used to assess the effects of interactions on the determination of particle size parameters from magnetic measurements. Investigation of the spatial correlation within the system reveals evidence of field induced particle agglomeration.     

Comparative analysis of the magnetization processes of the Gd3Ni and Gd3Co single crystals

The investigations and comparative analysis of the magnetization processes for Gd₃Ni and Gd₃Co single-crystal compounds are presented. The possible magnetic structures for both compounds are proposed and the features of the field-induced metamagnetic transitions are discussed on the basis of the possible magnetic structures. The anomalous behavior of the Gd₃Ni compound observed above the magnetic ordering temperature is very likely caused by the appearance of the nickel atoms magnetic moment and field-induced magnetic ordering.     

Surface ferromagnetism of Pd fine particles

We report clear evidence of the ferromagnetism of gas-evaporated Pd fine particles with a clean surface. The clean Pd particle is found to have a magnetic heterostructure: the surface of the particle is ferromagnetic and the rest is paramagnetic. The size dependence of the magnetic saturation component reveals that the ferromagnetic ordering occurs only on (100) facets of the particle and that the topmost two to five layers from the surface contribute to the ferromagnetism with a magnetic moment of (0.75+/-0.31)micro(B)/atom.     

Quantum quenches in a spinor condensate

We discuss the ordering of a spin-1 condensate when quenched from its paramagnetic phase to its ferromagnetic phase by reducing the magnetic field. We first elucidate the nature of the equilibrium quantum phase transition. Quenching rapidly through this transition reveals XY ordering either at a specific wave vector, or the "light-cone" correlations familiar from relativistic theories, depending on the end point of the quench. For a quench proceeding at a finite rate the ordering scale is governed by the Kibble-Zurek mechanism. The creation of vortices through growth of the magnetization fluctuations is also discussed. The long-time dynamics again depends on the end point, conserving the order parameter in a zero field, but not at a finite field, with differing exponents for the coarsening of magnetic order. The results are discussed in the light of a recent experiment by Sadler et al.     

Structure and magnetic ordering of superconducting GdBa2(Cu0.94Fe0.06)3O7 by Mössbauer spectroscopy

A coexistence of magnetic ordering and superconductivity has been found in GdBa₂(Cu_0.94Fe_0.06)₃O₇ at 4.2 K. The magnetic ordering is seen in the Fe moments using Mössbauer spectroscopy. The small Fe percentage was chosen to enable us to probe the crystalline and magnetic environment of an isolated Fe ion. Possible mechanisms responsible for the establishment of the magnetic order and its nature are discussed.     

Magnetic Ordering of Strongly Magnetized Massive Nd<Subscript>2</Subscript>Fe<Subscript>14</Subscript>B Magnets

The magnetic ordering of a strongly magnetized massive rectangular magnet is studied via magnetic force microscopy. The magnetic ordering structures on the magnet’s surface are determined. An attempt is made to interpret the observed magnetic ordering by analyzing the simplest magnetic ordering models theoretically.     

Recent topics in microstructure control by magnetic field in Ni<Subscript>2</Subscript>MnGa and CoPt and new transformation behavior in Ti-Ni-Fe alloys

Three topics related to solid-solid phase transformations are presented. The first topic is related to ferromagnetic shape memory alloys. The general condition for rearrangement of martensite variants by magnetic field is discussed quantitatively. The second topic is related to microstructure control of CoPt (tetragonal L1₀-type structure) during ordering heat-treatment under a magnetic field. We show that a single variant state is realized by magnetic field, and magnetic field is especially effective at the early stage of ordering. The third topic is related to the so-called precursor phenomena in Ti-Ni-Fe shape memory alloys. In the topic we will show the existence of a commensurate phase, which inherits the microstructure of the incommensurate phase and is probably different from the R-phase.     

Effect of short-range order on electronic and magnetic properties of disordered Co-based alloys

We here study electronic structure and magnetic properties of disordered CoPd and CoPt alloys using augmented space recursion technique coupled with the tight-binding linearized muffin tin orbital (TB-LMTO) method. Effect of short-range ordering present in disordered phase of alloys on electronic and magnetic properties has been discussed. We present results for magnetic moments, Curie temperatures and electronic band energies with varying degrees of short-range order for different concentrations of Co and try to understand and compare the magnetic properties and ordering phenomena in these systems.     

Re-entrant ferrimagnetism in TbMn6Ge6

The magnetic ordering of the hexagonal compound TbMn₆Ge₆ has been studied by neutron diffraction at various temperatures between 1.8 and 500 K. In almost the whole magnetically ordered regime the magnetic structures are incommensurate with the crystal lattice. The corresponding wave vector q₁ = (0,0,q_z) is strongly temperature dependent and decreases from q_z = 0.1307 r.l.u. at 1.8 K to q_z = 0.091 r.l.u. at 410 K. The low-temperature range (T < 85 K) is characterised by a triple ferrimagnetic spiral structure with net moment along the c-direction. At T_t = 85 K the net moment disappears and the magnetic ordering changes into a flat spiral structure that probably persists up to the magnetic ordering temperature, T_N = 450 K. Before reaching the magnetic ordering temperature, however, an additional ferrimagnetic component perpendicular to the c-direction develops, marking the onset of re-entrant ferrimagnetism. The resulting structure described by two propagation vectors corresponds to a distorted spiral. Various models are discussed. The observed re-entrant ferrimagnetism is in agreement with results of previously reported magnetic measurements.     

Magnetic material in head, thorax, and abdomen of Solenopsis substituta ants: a ferromagnetic resonance study

Ferromagnetic resonance temperature dependence is used to study the magnetic material in smashed head, thorax, and abdomen of Solenopsis substituta ants. These three body parts present the five lines previously observed in other social insects. The magnetic material content is slightly higher in heads with antennae than in abdomen with petiole. Isolated nanoparticle diameters were estimated as 12.5 +/- 0.1 and 11.0 +/- 0.2 nm in abdomen with petiole and head with antennae, respectively. The presence of linear chains of these particles or large ellipsoidal particles are suggested. A bulk-like magnetite particle was observed in the thorax. The Curie-Weiss, the structural-electronic and ordering transition temperatures were obtained in good agreement with those proposed for magnetite nanoparticles.     

Hyperfine interactions in the anisotropic layer compound FeOCl from57Fe Mössbauer studies

The anisotropic layer compound FeOCl has been synthesized by two different techniques to give, respectively, a large single crystal blade-like product (SC) and a polycrystalline powder product (PC), each of which was examined by temperature dependent⁵⁷Fe Mössbauer spectroscopy over the range 4.2≤T≤300 K. In particular, the onset of magnetic ordering on sample cooling (near 90 K) has been studied in detail, in the light of the 2-dimensional ordering of the paramagnetic ion spins in the crystallographica, c plane. The high temperature (～300 K) and low temperature (～4.2 K) Mössbauer parameters for the SC and PC material are identical within experimental error. The persistence in the spectra of the paramagnetic doublet due to h.s. Fe(III) below the magnetic ordering temperature in the PC material is shown to be consistent with the superparamagnetism of small particles in those samples.     

A phenomenological study of superconductivity in rare earth compounds

The effect of critical magnetic scattering is studied in paramagnetic phase of rare earth compounds showing superconductivity and magnetic order. If the exchange coupling between the conduction electrons and the magnetic ions is small the system becomes superconducting between two transition temperatures. The lower one is slightly higher than the magnetic ordering temperature and this is due to the critical magnetic scattering of the conduction electrons. The influence of the lifetime of one electron on the phase transition is briefly discussed.