In contrast to well studied multiferroic manganites with a spiral structure, the electric polarization in multiferroic borates is induced within collinear antiferromagnetic structure and can easily be switched by small static fields. Because of specific symmetry conditions, static and dynamic properties in borates are directly connected, which leads to giant magnetoelectric and magnetodielectric effects. Here we prove experimentally that the giant magnetodielectric effect in samarium ferroborate SmFe3(BO3)4 is of intrinsic origin and is caused by an unusually large electromagnon situated in the microwave range. This electromagnon reveals strong optical activity exceeding 120 degrees of polarization rotation in a millimeter thick sample
All-electrical control of a dynamic magnetoelectric effect is demonstrated in a classical multiferroic manganite DyMnO3, a material containing coupled antiferromagnetic and ferroelectric orders. Due to intrinsic magnetoelectric coupling with electromagnons a linearly polarized terahertz light rotates upon passing through the sample. The amplitude and the direction of the polarization rotation are defined by the orientation of ferroelectric domains and can be switched by static voltage. These experiments allow the terahertz polarization to be tuned using the dynamic magnetoelectric effect.PACS numbers: 75.85.+t, 78.20.Jq, 78.20.Ek, 75.30.Ds Electric and magnetic field control of the propagation and the polarization state of terahertz radiation is one of the prerequisites for continuous progress of modern electronics. A number of recent developments in this direction have been achieved using multiferroics, i.e. materials simultaneously revealing electric and magnetic ordering [1][2][3][4][5]. Several multiferroics provide not only a direct coupling between static electric and magnetic properties but also give a possibility to modify dynamic susceptibilities by external fields. Application of a static magnetic field to the multiferroic materials leads to dichroism in the terahertz range [6,7] or even to more complex effects like controlled chirality [8] or directional dichroism [9][10][11]. Electric control of terahertz radiation is more difficult to realize and it has been recently demonstrated in Raman scattering experiments [12].Dynamical properties of several multiferroic materials in the terahertz range are governed by novel magnetoelectric modes called electromagnons [13][14][15][16]. Electromagnons may be defined as collective excitations of the magnetic structure which are coupled to the electric dipole moment.They may be regarded as a mixture of magnons and phonons. In orthorhombic rare earth manganites RMnO 3 one generally observes several electromagnons in the terahertz and sub-terahertz range. A strong high frequency mode around 2-3 THz is well understood on the basis of a symmetric Heisenberg exchange (HE) coupling [17,18] as a zone edge magnon which can be excited by electric component of the electromagnetic radiation. A second intensive mode existing at 0.5-1 THz has been explained using the same mechanism but including a Brillouin zone folding due to modulation of the magnetic cycloid [18,19]. In the sub-terahertz frequency range a series of weaker modes is observed in optical [14,20] and neutron scattering experiments [21]. These modes are explained as the magnetic eigenmodes of the spin cycloid in RMnO 3 . Some of these modes may get an electrical dipole activity due to the relativistic Dzyaloshinskii-Moriya (DM) mechanism. Dynamic contributions due to this mechanism have been investigated both experimentally and theoretically [20,[22][23][24][25]. In spite of its weakness, the DM interaction is a promising mechanism especially in application to spiral magnets as it connects static spontaneous ...
As Grazing Incidence X-ray Fluorescence (GIXRF) analysis does not provide unambiguous results for the characterization of nanometre layers as well as nanometre depth profiles of implants in silicon wafers by its own, the approach of providing additional information using the signal from X-ray Reflectivity (XRR) was tested. As GIXRF already uses an X-ray beam impinging under grazing incidence and the variation of the angle of incidence, a GIXRF spectrometer was adapted with an XRR unit to obtain data from the angle dependent fluorescence radiation as well as data from the reflected beam. A θ-2θ goniometer was simulated by combining a translation and tilt movement of a Silicon Drift detector, which allows detecting the reflected beam over 5 orders of magnitude. HfO2 layers as well as As implants in Silicon wafers in the nanometre range were characterized using this new setup. A just recently published combined evaluation approach was used for data evaluation.
One of the most fascinating and counter-intuitive recent effects in multiferroics is the directional anisotropy, the asymmetry of light propagation with respect to the direction of propagation. In such case the absorption in a material can be different for opposite directions. Beside absorption, different velocities of light for different directions of propagation may be also expected, which is termed directional birefringence. In this work, we demonstrate large directional anisotropy in a multiferroic samarium ferroborate. The effect is observed for linear polarization of light in the range of millimeter-wavelengths, and it survives down to low frequencies. The dispersion and absorption close to the electromagnon resonance can be controlled by external magnetic field and is fully suppressed in one direction. By changing the geometry of the external field, samarium ferroborate shows giant optical activity, which makes this material to a universal tool for optical control: with a magnetic field as an external parameter it allows switching between two functionalities: polarization rotation and directional anisotropy.
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