arXiv subjects

S. Weber

Publications and source records attributed to S. Weber.

41 records · Page 3Linked to original sources

arXiv2006

Apparent giant dielectric constants, dielectric relaxation, and ac-conductivity of hexagonal perovskites La1.2Sr2.7BO7.33 (B = Ru, Ir)

We present a thorough dielectric investigation of the hexagonal perovskites La1.2Sr2.7IrO7.33 and La1.2Sr2.7RuO7.33 in a broad frequency and temperature range, supplemented by additional infrared measurements. The occurrence of giant dielectric constants up to 10^5 is revealed to be due to electrode polarization. Aside of dc and ac conductivity contributions, we detect two intrinsic relaxation processes that can be ascribed to ionic hopping between different off-center positions. In both materials we find evidence for charge transport via hopping of localized charge carriers. In the infrared region, three phonon bands are detected, followed by several electronic excitations. In addition, these materials provide further examples for the occurrence of a superlinear power law in the broadband ac conductivity, which recently was proposed to be a universal feature of all disordered matter.

cond-mat.str-el↗

arXiv2006

Experimental evidence for competition of antiferromagnetic and ferromagnetic correlations in HgCr2S4

A detailed study of poly- and single crystalline samples of the normal spinel HgCr2S4 is reported. The structural refinement reveals enhanced values of the atomic displacements suggesting closeness to a structural instability. Magnetization, electron-spin resonance and specific-heat studies document strong ferromagnetic fluctuations close to 50 K and the occurrence of complex antiferromagnetic order at TN = 22 K. We found highly unconventional behavior resembling properties of a non-collinear antiferromagnet and soft ferromagnet dependent on temperature and magnetic field. Even weak external magnetic fields disturb the antiferromagnetic order and strongly enhance the ferromagnetic correlations. The conductivity shows an insulating character with non-monotonous temperature behavior and a metal-to-insulator like transition at 80 K well above the magnetic transition. The observed anomalies are related to bond frustration due to competing magnetic exchange interactions between the Cr ions.

cond-mat.mtrl-sci↗

arXiv2006

Colossal magnetocapacitance and colossal magnetoresistance in HgCr2S4

We present a detailed study of the dielectric and charge transport properties of the antiferromagnetic cubic spinel HgCr2S4. Similar to the findings in ferromagnetic CdCr2S4, the dielectric constant of HgCr2S4 becomes strongly enhanced in the region below 60 - 80 K, which can be ascribed to polar relaxational dynamics triggered by the onset of ferromagnetic correlations. In addition, the observation of polarization hysteresis curves indicates the development of ferroelectric order below about 70 K. Moreover, our investigations in external magnetic fields up to 5 T reveal the simultaneous occurrence of magnetocapacitance and magnetoresistance of truly colossal magnitudes in this material.

cond-mat.str-el↗

arXiv2005

Multiferroic behavior in CdCr2X4 (X = S, Se)

The recently discovered multiferroic material CdCr2S4 shows a coexistence of ferromagnetism and relaxor ferroelectricity together with a colossal magnetocapacitive effect. The complex dielectric permittivity of this compound and of the structurally related CdCr2Se4 was studied by means of broadband dielectric spectroscopy using different electrode materials. The observed magnetocapacitive coupling at the magnetic transition is driven by enormous changes of the relaxation dynamics induced by the development of magnetic order.

cond-mat.str-el↗

arXiv1994

6Li Inelastic Form Factors in a Cluster Model

Longitudinal and transverse form factors are calculated for the transition into the low lying excited T=0 and T=1 states of 6Li in the framework of the resonating group model. All form factors are reproduced simultaneously using three cluster-wavefunctions. Meson exchange currents yield only minor corrections and do not lead to any specific structures at large momentum transfers.

nucl-th↗