RESUMO
The magnetoelectric properties of hexaferrite Ba0.5Sr1.5Zn2Fe12O22 are significantly improved by Al substitution and thermal annealing. Measuring the enhancement factor of 57Fe NMR, we found direct microscopic evidence that the magnetic moments of the L and S blocks are rotated by a magnetic field in such a way as to increase the net magnetic moment of a magnetic unit, even after the field is removed. Al substitution makes magnetoelectric property arise easily by suppressing the easy-plane anisotropy. The effect of thermal annealing is to stabilize the multiferroic state by reducing the number of pinning sites and the electron spin fluctuation. The transverse conic structure gradually changes to the alternating longitudinal conic structure where spins fluctuate more severely.
Assuntos
Alumínio/química , Eletricidade , Compostos Férricos/química , Radioisótopos de Ferro/química , Espectroscopia de Ressonância Magnética , Magnetismo , Bário/química , Modelos Moleculares , Estrôncio/química , Temperatura , Zinco/químicaRESUMO
We present the spin dynamics of isolated donor electrons in phosphorus-doped silicon at low temperature and in a high magnetic field. We performed a steady-state electron spin resonance (ESR) on the sample with a dopant concentration of 6.5 × 10(16) cm(- 3) in a high field of 2.87 T (80 GHz) and at temperatures from 48 down to 1.8 K. As the temperature decreases below 16 K, the resonance spectral line changes from the usual derivative form characteristic of absorptions. Very long spin-lattice relaxation time T(1) at low temperature gives rise to rapid passage effects and results in a dramatic change in the line shape and intensity as a function of temperature. We show that the numerical analysis based on the passage effects well explains the observed spectral changes with temperature. The spin-lattice relaxation time T(1) is derived by numerical fit to the experimental data. We discuss the dynamic nuclear polarization of (31)P nuclear spins which shows up as asymmetric intensities of the hyperfine-split ESR resonance lines.