P. Cevc

Weak ferromagnetism and ferroelectricity in K3Fe5F15

Here, we report on the observation of a weak ferromagnetic transition at TN=122K in a K3Fe5F15 system which is ferroelectric and ferroelastic below Tc=490K. The magnetization and the susceptibility continuously increase with decreasing T down to 2K. The Mossbauer spectra show a spontaneous magnetic ordering and at least three sites corresponding to Fe2+ and Fe3+. The ratio between Fe2+ and Fe3+ is 60:40. At 6K, there are two magnetically ordered sextets with internal fields of 585 and 263kOe. The “slim” hysteresis loops observed are as well characteristic of weak ferromagnetism. At 122K and at low frequencies, the system shows dielectric anomaly characteristic of magnetoelectric behavior.

Study of the Arrangement of Crystallites in y-Irradiated Human Enamel by Electron Paramagnetic Resonance

The arrangement of tooth enamel microcrystals has been studied on CO3 3- bound electrons by electron paramagnetic resonance. It was found that noncarious human maxillary central incisors have a greater degree of alignment of tooth enamel microcrystals than the carious ones. The outermost surface layer of enamel showed a greater crystallite degree of alignment than other parts.

Mirocrystal Arrangement in Human Deciduous Dental Enamel Studied by Electron Paramagnetic Resonance

The arrangement of microcrystallites in human deciduous enamel was studied by electron paramagnetic resonance using a stable CO33––radiation centre as a probe. Enamel

Magnetic properties of multiferroic K3Cr2Fe3F15

The local electronic and structural as well as the macroscopic magnetic properties of K3Cr2Fe3F15 have been studied between room temperature and 4 K. The system has been found to be isostructural with ferroelectric and weakly ferrimagnetic K3Fe5F15 above the ferroelectric transition temperature Tc. The X-band and 216 GHz Cr3+ electron paramagnetic resonance (EPR) spectra as well as the magnetic susceptibility and Mossbauer data show the existence of two magnetic relaxor type transitions around 37 and 17 K. The K39 magic angle sample spinning NMR, EPR, and the Mossbauer data further demonstrate the existence of two nonequivalent Fe, Cr, and K sites in the unit cell as well as the presence of rapid exchange at higher temperatures. The observation of the Fe2+ EPR and Mossbauer spectra shows that the Fe2+ ion is in a high spin state.

Diffusion of spin probes in tissues measured by field-gradient EPR

Abstract A linear magnetic field gradient was superimposed on a main static field to resolve the spatial distribution of diffusing paramagnetic molecules. The diffusion coefficient and distribution function were evaluated from the field-gradient electron paramagnetic spectra by comparison with spectra calculated from a corresponding model. Adipose tissue penetration of spin-labeled methyl ester of palmitic acid was measured.

Electron paramagnetic resonance and Mössbauer study of antiferromagnetic K3Cu3Fe2F15

The electron paramagnetic resonance (EPR) spectra of K3Cu3Fe2F15 consist above 85 K of a superposition of two Lorentzians with different intensities, T-dependences, linewidths, and g-factors. The broad line shows an antiferromagnetic (AFM) behavior and the narrow one shows a paramagneticlike behavior. The Mossbauer spectra consist at room temperature of two quadrupolar doublets and below 77 K of two magnetic sextets and one quadrupolar doublet. Below 85 K the broad line EPR disappears and the intensity of the narrow line increases nearly exponentially with decreasing temperature. The broad EPR line originates from regions with local AFM order, whereas the narrow line comes from regions without AFM order, e.g., grain boundaries.

Technology of double parallel pyroelectric detector

Abstract Pyroelectric infrared detectors are efficient and cheap sensors for many applications. In order to acquire a common optic mode rejection capability, the double serial or parallel construction of active electrodes has been employed. The latter type is difficult to construct due to connection between the electrodes. The usual solution is to mount the two separate thin crystalline active elements on the separate holders. This technique lacks uniformity and precise cancellation of common mode. We have found the way to construct and fabricate the double parallel detector formed on a single piece of thin pyroelectric material. In this paper we describe the technology as well as the results of the detector parameter measurements.

EPR study of central peak dynamics around the AsO44− center in KDA–KDP and ADA–ADP mixed crystals

Using the lifetime effects in the domain splitting of the ESP spectra as a detector of the polarization fluctuations around an AsO4−4 center, we have studied the dependence of the temperature T—where the local tetragonal symmetry of the high temperature paraelectric phase is broken on the time scale of the ESP experiment—on Tc in mixed KH2AsO4–KH2PO4 (KDA–KDP) and NH4H2AsO4–NH4H2PO4 (ADA–ADP) crystals. T decreases with Tc in KDA–KDP and increases with Tc in ADA–ADP crystals though the domain splitting is nearly constant. This can be understood only if the central peak width depends on the host lattice and thus varies with Tc. The width of the central peak in the polarization fluctuation spectrum, which changes in KDA from 280 MHz at 45 °C to 6 MHz at −90 °C does not depend on the concentration of the paramagnetic defect centers within the range studied. The results can be explained by a model where in the high temperature phase the mobile clusters of the low temperature phase are trapped by the defect cen...

NMR Imaging in Dentistry: Relaxation and Diffusion Studies

Magnetic resonance imaging has been widely used for medical diagnosis in recent years. The knowledge of the proton spin-lattice relaxation time, T1, represents the basis for NMR imaging. In the present study, we measured T1 in saliva, gingival fluid, gingival blood, and inflamed gingiva by means of a pulsed NMR Fourier-transform spectrometer. From several measurements, we found the following average T1 values: in saliva, T1 = 2550 msec; in gingival fluid, T1 = 2085 msec; in gingival blood, T1 = 1515 msec; and in inflamed gingiva samples, T1 = 840 msec. In addition, electron paramagnetic resonance imaging was used to demonstrate the in vitro diffusion processes of spin-labeled molecules into tooth enamel by application of the linear magnetic field gradient to a conventional EPR spectrometer. The diffusion coefficient for the nitroxide spin-labeled molecules into tooth enamel was evaluated as D = 10-7 cm2 sec-1.

Tl2+ EPR detection of glassy behavior in ADPx - RDP1−x and deuteration effects in the phase diagram of ADx − RDA1−x

Abstract Using the large (≈ 100 GHz) hyperfine coupling of the Tl2+ (6s1) ion as a spin probe, we have investigated the evolution of glassy behavior in (NH4) xRb1−xH2 PO4 single crystals. Also reported is a microwave dielectric loss determination of the phase diagram of (ND4) xRb1−xD2AsO4. The glass formation temperature, Tc, is found to be significantly higher and the glass phase range narrower in the deuterated arsenate system than in the corresponding protonated arsenate system. Both of these phenomena are tentatively interpreted in terms of a random bond version of the Ising model in a transverse tunneling field.