M. Koralewski

The Faraday effect of natural and artificial ferritins

Measurements of the Faraday rotation at room temperature over the light wavelength range of 300-680 nm for horse spleen ferritin (HSF), magnetoferritin with different loading factors (LFs) and nanoscale magnetite and Fe(2)O(3) suspensions are reported. The Faraday rotation and the magnetization of the materials studied present similar magnetic field dependences and are characteristic of a superparamagnetic system. The dependence of the Faraday rotation on the magnetic field is described, excluding HSF and Fe(2)O(3), by a Langevin function with a log-normal distribution of the particle size allowing the core diameters of the substances studied to be calculated. It was found that the specific Verdet constant depends linearly on the LF. Differences in the Faraday rotation spectra and their magnetic field dependences allow discrimination between magnetoferritin with maghemite and magnetite cores which can be very useful in biomedicine.

The effect of uniaxial pressure on the ferroelectric phase transition of TGSe crystals

Isobaric studies of the influence of uniaxial pressure on the transitions of pure TGSe crystals for the three directions are reported. The critical exponents, and , from dielectric constant and hysteresis loop measurements, as well as the coefficients and of the fourth and sixth powers of P in the free-energy expansion under uniaxial pressure were determined. It has been found that uniaxial pressure applied along the -axis keeps the transition near a tricritical point for 0 < X < 200 bar, but that when it is applied along the b- and c-axes it strengthens the second-order phase transition behaviour. The tricritical behaviour of TGSe crystals is discussed and a possible driving mechanism for the change in order of the phase transition is proposed.

Thermal hysteresis and quadrupole interactions in ferroelectric transitions

Abstract It is shown that a selfconsistent calculation of the maximum amount of thermal hystersis accompanying discountinous ferroelectric transtion can be made if one takes into account the quadrupolar contribution to the effective ferroelectric field. Comparison of calculated and observed thermal hystersis in sereral ferroelectrics belonging to different families shows fair agreement.

The influence of an electric field on the latent heat of the ferroelectric phase transition in KDP

The specific heat, heat flux (DTA trace) and dielectric constant of KDP ferroelectric crystal have been measured simultaneously for various electric fields with a conduction calorimeter. The specific heat presents a strong anomaly, but these simultaneous measurements allow us to evaluate the latent heat accurately. The latent heat decreases with field, and the value of the critical electric field—that where the latent heat disappears—is estimated to be (0.44 ± 0.03) kV cm−1. Incidentally, we have measured simultaneously the dielectric permittivity, which suggests that latent heat is developed as domains are growing.

First order transitions by conduction calorimetry: Application to deuterated potassium dihydrogen phosphate ferroelastic crystal under uniaxial pressure

The specific heat c and the heat power W exchanged by a Deuterated Potassium Dihydrogen Phosphate ferroelectric-ferroelastic crystal have been measured simultaneously for both decreasing and increasing temperature at a low constant rate (0.06 K/h) between 175 and 240 K. The measurements were carried out under controlled uniaxial stresses of 0.3 and 4.5±0.1 bar applied to face (110). At Tt=207.9 K, a first order transition is produced with anomalous specific heat behavior in the interval where the transition heat appears. This anomalous behavior is explained in terms of the temperature variation of the heat power during the transition. During cooling, the transition occurs with coexistence of phases, while during heating it seems that metastable states are reached. Excluding data affected by the transition heat, the specific heat behavior agrees with the predictions of a 2-4-6 Landau potential in the range of 4–15 K below Tt while logarithmic behavior is obtained in the range from Tt to 1 K below Tt. Data ...

Magnitude of electrogyration effect in crystals

Abstract Electrogyration Millers delta Δg is checked for more than 50 crystals. The corelation between Δg and other quantites is discussed, similar relation for quadratic electrogyration is introduced.

Electrogyration of pure and X-Irradiated TGS crystals

Abstract Dispersion of optical rotatory power δ, temperature dependence of δ and electrogyration of hysteresis loops of pure and X-irradiated TGS crystals have been measured, The relation between OA and Ps and the origin of OA in TGS crystal is discussed.

On the adsorption of magnetite nanoparticles on lysozyme amyloid fibrils

An adsorption of magnetic nanoparticles (MNP) from electrostatically stabilized aqueous ferrofluids on amyloid fibrils of hen egg white lysozyme (HEWL) in 2mg/mL acidic dispersions have been detected for the MNP concentration range of 0.01-0.1vol.%. The association of the MNP with amyloid fibrils has been characterized by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and magneto-optical measurements. It has been observed that the extent of adsorption is determined by the MNP concentration. When increasing the MNP concentration the formed aggregates of magnetic particles repeat the general rod-like structure of the fibrils. The effect is not observed when MNP are mixed with the solution of lysozyme monomers. The adsorption has been investigated with the aim to clarify previously found disaggregation activity of MNP in amyloid fibrils dispersions and to get deeper insight into interaction processes between amyloids and MNP. The observed effect is also discussed with respect to potential applications for ordering lysozyme amyloid fibrils in a liquid crystal phase under external magnetic fields.

Phenomenological rules for the computation of magneto-electric susceptibilities

Applying the model of the anharmonic oscillator, phenomenological expressions were derived, allowing calculation of the components of tensors describing non-linear magneto-electric susceptibilities. Detailed calculations were carried out for the pseudo-tensor of fourth order ηeeem in terms of which magneto-optical birefringence and rotation are expressed for the monocrystals KDP, DKDP, ADP, KDA, LiNbO3, LiTaO3 and NaClO3. From the results obtained it follows that non-linear magneto-electric susceptibilities, which are described by the pseudo-tensor ηeeem are of the order of 10−16 m V−1T−1.

Influence of Deuteration, Electric Field and Uniaxial Stress on Tricritical Phase Transition of TGSe: Calorimetric Study

The tricritical phase transition of ferroelectric triglycine selenate (TGSe) has been investigated under the influence of weak uniaxial stress and electric fields by means of a high sensitive calorimetric technique. The effect of deuteration on the latent heat has been also analysed.