Compact solid-state sources of terahertz (THz) radiation are being sought for sensing, imaging, and spectroscopy applications across the physical and biological sciences. We demonstrate that coherent continuous-wave THz radiation of sizable power can be extracted from intrinsic Josephson junctions in the layered high-temperature superconductor Bi2Sr2CaCu2O8. In analogy to a laser cavity, the excitation of an electromagnetic cavity resonance inside the sample generates a macroscopic coherent state in which a large number of junctions are synchronized to oscillate in phase. The emission power is found to increase as the square of the number of junctions reaching values of 0.5 microwatt at frequencies up to 0.85 THz, and persists up to ∼50 kelvin. These results should stimulate the development of superconducting compact sources of THz radiation.

http://absimage.aps.org/image/MAR08/MWS_MAR08-2007-004672.pdf

Emission of Coherent THz-Radiation from Superconductors.

Multiferroic bismuth ferrite-based materials for multifunctional applications: Ceramic bulks, thin films and nanostructures

We report here enhancement of ferromagnetism in pure ZnO upon thermal annealing with the ferromagnetic transition temperature Tc above room temperature. We observe a finite coercive field upto 300K and a finite thermoremanent magnetization upto 340K for the annealed sample. We propose that magnetic moments can form at anionic vacancy clusters. Ferromagnetism can occur due to either superexchange between vacancy clusters via isolated F+ centers, or through a limited electron delocalization between vacancy clusters. Isolated vacancy clusters or isolated F+ centers give rise to a strong paramagnetic like behaviour below 10K.

Enhancement of ferromagnetism upon thermal annealing in pure ZnO

Matter manipulation with extreme terahertz light : Progress in the enabling THz technology

Enhancement of magnetoelectric properties of (1-x)Mn0.5Zn0.5Fe2O4-xBa0.85Sr0.15Ti0.9Hf0.1O3 composite ceramics

This study reports the various physical properties of (1�x)(0.3CoFe2O4-0.7BiFeO3)-xBaTiO3 composites (equivalently denoted as 0.3CFO-0.7BFO/BT) with the compositions x=0, 0.30, 0.35, 0.40 and 1.0. The composites are synthesized through a hybrid processing technique in which 0.3CFO–0.7BFO is prepared through a sol-gel process, and BT is processed through a solid state reaction method. Subsequently, the effects of the addition of BT on the structural, dielectric, magnetic and magneto-dielectric properties of 0.3CFO–0.7BFO have been investigated for various BT concentrations. The Rietveld refinement analysis of x-ray diffraction patterns reveals the structural distortion in the BFO phase with the addition of BT, while no such distortion has been observed for the CFO phase. Energy dispersive spectroscopy confirms the presence of two types of grains that correspond to the 0.3CFO–0.7BFO and BT phases in field emission scanning electron micrographs of the composites. Improved dielectric properties have been observed, which are associated with the improved density of composites with the addition of BT. Measurements of the magnetic and ferroelectric hysteresis loops at room temperature indicate that the composites exhibit ferroelectricity and ferromagnetism simultaneously at room temperature. An increase of the electric polarization has been observed due to structural distortion arising with the addition of BT. The significant dependence of the dielectric constant on the magnetic field has been observed in the prepared composites. The highest value of the magneto-dielectric response (3.2%) has been observed for a 40 mol% addition of BT.

https://iopscience.iop.org/article/10.1088/0964-1726/23/10/105024/pdf

Effect of BaTiO 3 addition on structural, multiferroic and magneto-dielectric properties of 0.3CoFe 2 O 4 -0.7BiFeO 3 ceramics

A class of hybrid composites (x)Ni0.75Zn0.25Fe2O4?(1???x)Ba(Ti 0.85Zr 0.15)O 3 (for x variations 0, 0.20, 0.30 and 0.40) synthesized via a solid state reaction method is investigated. The structural analysis was carried out using an x-ray diffraction graph which reveals a mixed phase of the hybrid composites with spinel phase for ferrite component and perovskite phase for the ferroelectric component. The microstructural analysis and grain size determination is carried out using a field emission scanning electron microscope (FESEM). The relative dielectric constant with frequency variation (in the range of 100?Hz?1?MHz) and temperature at three fixed frequencies (100?Hz, 1?KHz and 10?KHz) is studied. The magnetic properties such as saturation magnetization (Ms ) and magnetic moment (?B) are calculated from the magnetic hysteresis loops obtained using a vibrating sample magnetometer (VSM). The value of remnant polarization for pure BZT is found to be 6.18??C?cm?2 and as the content of ferrite phase is increased up to 40?mol%, this value decreases. The magnetoelectric effect is studied using magnetocapacitance which takes a maximum value for 40?mol% addition of ferrite.

https://iopscience.iop.org/article/10.1088/0964-1726/21/11/115021/pdf

Study of structural, dielectric and magnetic behaviour of Ni0.75Zn0.25Fe2O4–Ba(Ti0.85Zr0.15)O3 composites

The magnetoelectric composites of spinel ferrite Ni0.75Zn0.25Fe2O4 (NZF) and BiFeO3 (BFO) with general formula xNi0.75Zn0.25Fe2O4 + (1 − x)BiFeO3 (x = 0, 0.10, 0.20, and 0.30) have been prepared via hybrid processing route. Subsequently, the effects of addition of NZF on structural, dielectric, magnetic, magnetoelectric, and optical properties of BFO have been investigated, and significant enhancements have been observed in physical observables such as grain size, dielectric constant, magnetization, and polarization in ferroelectric hysteresis loops. The variation of magnetization with temperature indicates the presence of spin glass behavior along with the ferromagnetic component. The magnetoelectric coupling is found with a value of magnetocapacitance to be 4.6 % for 30 mol% addition of NZF. The optical properties of the composites are also studied using UV–Vis diffuse reflectance spectroscopy, Photoluminescence spectroscopy, and FTIR spectroscopy.

Structural, dielectric, magnetic, and optical properties of Ni0.75Zn0.25Fe2O4–BiFeO3 composites

Three-phase magnetoelectric composites (1 - x) (0.7BiFeO3-0.3CoFe2O4)-xPbTiO3 (or equivalently written as (1 - x)(0.7BFO-0.3CFO)-xPT) with x variations 0, 0.30, 0.35, 0.40, 0.45, and 1.0 were synthesized using hybrid pro- cessing route. The effects of PT addition on structural, mul- tiferroic, and optical properties have been subsequently investigated. A detailed Rietveld refinement analysis of X-ray diffraction patterns has been performed, which confirms the presence of structural phases of individual constituents in the composites. Field emission scanning electron microscopy images are taken for microstructural analysis and grain size determination. Transmission electron microscopy analysis of 0.3CFO-0.7BFO reveals the average particle size to be lying in the window of 10-15 nm. The temperature-dependent dielectric constant at various frequencies (1, 10, 50, 100, and 500 kHz) has been studied, and the dielectric study reveals the increase of dielectric constant and decrease of average dielectric loss of composites with incorporation of PT content. Room temperature ferromagnetic behavior of composites is confirmed through the observation of magnetization versus magnetic field (M-H) hysteresis loops. The variation of magnetization with temperature indicates the presence of spin glass behavior in composites. Magnetoelectric coupling is evidenced in the composites through the observation of dependence of the dielectric constant on magnetic field, and magnetodielectric response of 2.05 % is observed for 45 mol% addition of PT content. The fractional change of magnetic field-induced dielectric constant can also be expressed as Der * cM 2 , and the value of c is found to be *1.08 9 10 -2 (emu/g) -2 for composite with x = 0.40. Fourier transformed infrared spectroscopy of samples is car- ried out to analyze various bonds formation in the composites.

Nidhi Adhlakha

Papers

Effect of BaTiO 3 addition on structural, multiferroic and magneto-dielectric properties of 0.3CoFe 2 O 4 -0.7BiFeO 3 ceramics

Study of structural, dielectric and magnetic behaviour of Ni0.75Zn0.25Fe2O4–Ba(Ti0.85Zr0.15)O3 composites

Structural, dielectric, magnetic, and optical properties of Ni0.75Zn0.25Fe2O4–BiFeO3 composites

BiFeO3–CoFe2O4–PbTiO3 composites: structural, multiferroic, and optical characteristics

Multiferroic and magnetoelectric properties of BiFeO3-CoFe2O4-poly(vinylidene-flouride) composite films