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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 Mössbauer data show the existence of two magnetic relaxor type transitions around 37 and 17 K. The 39K magic angle sample spinning NMR, EPR, and the Mössbauer 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 Mössbauer spectra shows that the Fe2+ ion is in a high spin state. [ABSTRACT FROM AUTHOR]

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 Mössbauer 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. [ABSTRACT FROM AUTHOR]

To check on the nature of the weak magnetic order in polycrystalline magnetoelectric Pb(Fe1/2Nb1/2)O3 the X-band, Q-band, and far infrared electron paramagnetic resonance (EPR) spectra have been measured between 4 and 600 K and compared with magnetic susceptibility and magnetization data. The asymmetric line shapes can be simulated at higher temperature by thermally fluctuating superparamagnetic nanoclusters. The pronounced temperature dependence of the position of the spectra demonstrates the presence of an internal magnetic field which is small but nonzero even at room temperature, i.e., far above the antiferromagnetic transition. The electronic spin-spin exchange has been found to be in the terahertz range. The magnetization data reveal a weak ferromagnetism even above 300 K and a break in the temperature dependence of susceptibility at the paramagnetic to ferromagnetic transition. [ABSTRACT FROM AUTHOR]

The frequency and temperature dependences of the magnetic susceptibility and the ac electrical conductivity in magnetoelectric [K.sub.3][Fe.sub.3.sup.II][Cr.sub.2.sup.III][F.sub.15] are examined. The analysis of the temperature dependence of the universal dielectric response (UDR) parameter s in terms of the theoretical model for tunneling of small polarons has shown that below 200 K, the mechanism has governed the charge transport in the magnetoelectric fluoride system.

The electron paramagnetic resonance (EPR) spectra of [K.sub.3][Cu.sub.3][Fe.sub.2][F.sub.15] consist above 85 K of a superposition of two Lorentzians with different intensities and the broad line has shown an antiferromagnetic (AFM) behavior. The broad EPR line has originated from regions with local AFM order, whereas the narrow line has come from regions without AFM order.

Broad and frequency dependent maxima observed in both the electric and magnetic susceptibilities for 0.3Pb([Fe.sub.1/2][Nb.sub.1/2])[O.sub.3]-0.7Pb([Mg.sub.1/2][W.sub.1/2])[O.sub.3] solid solution, magnetic and electric relaxor is reported. The magnetoelectric coupling in system is found to be negligibly small in spite of its multiferroic properties.

The nature of the weak magnetic order in polycrystalline magnetoelectric Pb([Fe.sub.1/2][Nb.sub.1/2])[O.sub.3] is studied by measuring the Q-band, X-band and far infrared electron paramagnetic resonance (EPR) spectra between 4 and 600 K. The electronic spin-spin exchange is found to be in the terahertz range and the magnetization data has shown a weak ferromagnetism even above 300 K and a break in the temperature dependence of susceptibility at the paramagnetic to ferromagnetic transition.

The frequency and temperature dependences of the magnetic susceptibility and the ac electrical conductivity in magnetoelectric K3FeII3CrIII2F15 were investigated. The zero-field-cooled-field-heated magnetic susceptibility reveals phase transitions at 14.2 and 36.6 K. The phase below 36.6 K is ferromagnetic. At temperatures below 200 K, the ac conductivity and dielectric constant follow the universal dielectric response (UDR), being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that below 200 K, this mechanism governs the charge transport in the magnetoelectric fluoride system. [ABSTRACT FROM AUTHOR]

0.3Pb(Fe1/2Nb1/2)O3–0.7Pb(Mg1/2W1/2)O3 solid solution is a magnetic and electric relaxor which shows broad and frequency dependent maxima in both the electric and magnetic susceptibilities. In spite of its multiferroic properties, i.e., irrespective of magnetic and electric ordering, the magnetoelectric coupling in this system is negligibly small. [ABSTRACT FROM AUTHOR]

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 Mössbauer data show the existence of two magnetic relaxor type transitions around 37 and 17 K. The 39K magic angle sample spinning NMR, EPR, and the Mössbauer 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 Mössbauer spectra shows that the Fe2+ ion is in a high spin state. [ABSTRACT FROM AUTHOR]

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 Mössbauer 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. [ABSTRACT FROM AUTHOR]

To check on the nature of the weak magnetic order in polycrystalline magnetoelectric Pb(Fe1/2Nb1/2)O3 the X-band, Q-band, and far infrared electron paramagnetic resonance (EPR) spectra have been measured between 4 and 600 K and compared with magnetic susceptibility and magnetization data. The asymmetric line shapes can be simulated at higher temperature by thermally fluctuating superparamagnetic nanoclusters. The pronounced temperature dependence of the position of the spectra demonstrates the presence of an internal magnetic field which is small but nonzero even at room temperature, i.e., far above the antiferromagnetic transition. The electronic spin-spin exchange has been found to be in the terahertz range. The magnetization data reveal a weak ferromagnetism even above 300 K and a break in the temperature dependence of susceptibility at the paramagnetic to ferromagnetic transition. [ABSTRACT FROM AUTHOR]

The frequency and temperature dependences of the magnetic susceptibility and the ac electrical conductivity in magnetoelectric K3FeII3CrIII2F15 were investigated. The zero-field-cooled-field-heated magnetic susceptibility reveals phase transitions at 14.2 and 36.6 K. The phase below 36.6 K is ferromagnetic. At temperatures below 200 K, the ac conductivity and dielectric constant follow the universal dielectric response (UDR), being typical for hopping or tunneling of localized charge carriers. A detailed analysis of the temperature dependence of the UDR parameter s in terms of the theoretical model for tunneling of small polarons revealed that below 200 K, this mechanism governs the charge transport in the magnetoelectric fluoride system. [ABSTRACT FROM AUTHOR]