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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 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]

We show that the misfit strain due to the film-substrate lattice mismatch strongly increases the value of the quadratic magnetoelectric coupling. The coupling, size effects, and misfit strains cause strong changes in the phase diagrams of ferroic films at zero external magnetic and electric fields. The antiferromagnetic to ferromagnetic or ferrimagnetic phase transitions for compressive or tensile misfit strains open the way for the tailoring of magnetic and electric properties of ferroic films leading to advanced applications. [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]

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]

We show, that in a substance with mixed-valence ions, which can supply free carriers and have electric dipole and spin moments, three types of long-range order (ferromagnetic, ferroelectric and magnetoelectric (ME)) can occur at low temperatures. The origin of the effect is that free charge carriers can mediate the multiferroic behavior via spin - spin (RKKY), dipole-dipole and dipole - spin interactions. We show that there is an optimal carrier concentration, at which the strength of ME interaction is maximal and comparable to that of RKKY interaction. Our analysis shows that disorder and finite conductivity in the above substances does not suppress multiferroic effects. [ABSTRACT FROM AUTHOR]

An anomaly in the magnetic susceptibility has been observed at and below the paraelectric - ferroelectric transition in polycrystalline Pb(Fe1/2Nb1/2)O3. The results are indicative of magnetoelectric coupling of the form P2M2. The non-linear relation between the induced magnetization and the applied magnetic field demonstrates the presence of large superparamagnetic clusters embedded in a paramagnetic medium over the whole ferroelectric phase, i.e. far above the antiferromagnetic transition temperature TN. [ABSTRACT FROM AUTHOR]

We present electric and magnetic properties of 0.8Pb(Fe1/2Nb1/2)O3–0.2Pb(Mg1/2W1/2)O3 films epitaxially grown on (001) SrTiO3 substrates using pulsed laser deposition. A narrow deposition window around 710 °C and 0.2 mbar has been identified to achieve epitaxial single-phase thin films. A typical Vogel–Fulcher relaxorlike dielectric and magnetic susceptibility dispersion is observed, suggesting magnetoelectric relaxor behavior in these films similar to the bulk. We determine a magnetic cluster freezing temperature of 36 K, while observing weak ferromagnetism via magnetic hysteresis loops up to 300 K. [ABSTRACT FROM AUTHOR]

Ferromagnetic spin-wave resonance has been observed in BiFeO3 nanoparticles with a size smaller than a critical size. The Heusler alloy Ni2MnGa has been studied too. The ferromagnetic resonance intensity of Ni2MnGa layers is much higher than that of BiFeO3. It is so high that even a single monolayer can be studied. [ABSTRACT FROM AUTHOR]

The measured 13C NMR spectra in the organic ferromagnet TDAE-C60 have been simulated in the temperature range between room temperature and 4 K. It is shown that the sudden increase in the inhomogeneous 13C NMR line width and the corresponding changes of the 13C NMR line shape deep in the ferromagnetic phase can be explained by the freezing out of the pseudo-rotations of the axes of the Jahn–Teller distortions of the C60- ions. A strong correlation between spin ordering and orientational ordering has been found. [Copyright &y& Elsevier]