Dynamic magnetoelectric effect in terbium molybdate

The electric polarization induced in ferroelectric terbium molybdate by a magnetic field linearly varying with time is measured. The measurements are performed in fields up to 19 T at different specified rates of change in the magnetic field at temperatures of 273 and 219 K. The results obtained indicate that there are magnetoelectric effects of two types. One of them is a conventional magnetoelectric effect, which is appropriately referred to as the static magnetoelectric effect. The other effect is characterized by the fact that the electric polarization increases with an increase in the rate of change in the magnetic field and relaxes with time to zero at a fixed nonzero field. This phenomenon is termed the dynamic magnetoelectric effect.     

Observation of magnetoelectric directional anisotropy

We report the first observation of a new optical phenomenon, magnetoelectric directional anisotropy (MEA). MEA is a polarization-independent anisotropy which occurs in crossed electric field E and magnetic field B perpendicular to the wave vector k of the light. It is described by a contribution to the refractive index of the form (delta)n=(gamma)k x E x B. Our experiment was performed on a Er(1.5)Y(1.5)Al(5)O(12) crystal, but MEA should exist in all media. The relation of this new effect with recently discovered magnetoelectric birefringence is discussed.     

Helikonen in Metallen

Zusammenfassung Bowers, Legendy undRose haben kürzlich an Natrium einen neuen galvanomagnetischen oszillatorischen Effekt entdeckt. Diese Oszillationen, nachAigrain „Helikonen” genannt, wurden nun auch in Indium, Aluminium und Kupfer nachgewiesen. Der Effekt kann rein klassisch, ausgehend von der Boltzmann-Gleichung und mit Hilfe der Maxwell-Gleichungen, verstanden werden. Er stellt eine neue Methode zur Bestimmung des Hall-Koeffizienten von Metallen in hohen Magnetfeldern dar.

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Recently, a new oscillatory galvanomagnetic effect has been detected in metallic sodium byBowers, Legendy andRose. These oscillations called “Helicon-oscillations” have now been found in indium, aluminium and copper as well. The effect can be completely understood in a classical way, starting from the Boltzmann equation and using Maxwell's equations. It provides a new method of determining the Hall coefficient of metals in high magnetic fields.

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Résumé Bowers, Legendy etRose ont récemment découvert dans le sodium un nouvel effet oscillatoire. Ces oscillations, appelées parAigrain “Hélicons”, ont pu être observées également dans l'aluminium, l'indium et le cuivre. L'effet peut être expliqué classiquement à l'aide des équations de Maxwell en partant de l'équation de Boltzmann. Il représente une nouvelle méthode pour déterminer le coefficient de Hall des métaux dans des champs magnétiques élevés.

     

Freie Weglängen für die elektrische und die thermische Leitfähigkeit

The electronic mean free path for the electrical and thermal conductivity of indium has been determined using size effect measurements on thin wires. In the temperature range investigated (0°<T<Θ/20,Θ: Debye-temperature) where the electron-phonon collisions are inelastic. the two mean free paths are different. There exists a simple relation between the mean free paths and the Lorenz-number which can be observed experimentally. The difference in the two mean free paths can also be seen using size effect measurements in strong longitudinal magnetic fields. The magnetic field dependence of the Lorenz-number has been measured.     

Determination of landau level lifetimes in n-GaAs

The lifetime of electrons in the first excited Landau level of n-GaAs is determined from a combination of measurements of far infrared cyclotron resonance induced absorption and conductivity change. Values of T₁ of the order of 10^?8s for densities of excited electrons of 10¹¹ cm^?3 and a temperature dependence of T^?2.7 are found. An upper limit for the N = 0 Landau level to donor recombination time of the order of 10^?9s was derived from pulsed conductivity measurements.