arXiv subjects

K. Flachbart

Publications and source records attributed to K. Flachbart.

24 records · Page 2Linked to original sources

arXiv2007

Magnetic structure and phase diagram of TmB4

Magnetic structure of single crystalline TmB4 has been studied by magnetization, magnetoresistivity and specific heat measurements. A complex phase diagram with different antiferromagnetic (AF) phases was observed below TN1 = 11.7 K. Besides the plateau at half-saturated magnetization (1/2 MS), also plateaus at 1/9, 1/8 and 1/7 of MS were observed as function of applied magnetic field B//c. From additional neutron scattering experiments on TmB4, we suppose that those plateaus arise from a stripe structure which appears to be coherent domain boundaries between AF ordered blocks of 7 or 9 lattice constants. The received results suggest that the frustration among the Tm3+ magnetic ions, which maps to a geometrically frustrated Shastry-Sutherland lattice lead to strong competition between AF and ferromagnetic (FM) order. Thus, stripe structures in intermediate field appear to be the best way to minimize the magnetostatic energy against other magnetic interactions between the Tm ions combined with very strong Ising anisotropy.

cond-mat.str-el↗

arXiv2007

Anomalous magnetoresistance of EuB$_{5.99}$C$_{0.01}$: Enhancement of magnetoresistance in systems with magnetic polarons

We present results of measurements of electrical, magnetic and thermal properties of EuB$_{5.99}$C$_{0.01}$. The observed anomalously large negative magnetoresistance as above, so below the Curie temperature of ferromagnetic ordering $T_C$ is attributed to fluctuations in carbon concentration. Below $T_C$ the carbon richer regions give rise to helimagnetic domains, which are responsible for an additional scattering term in the resistivity, which can be suppressed by a magnetic field. Above $T_C$ these regions prevent the process of percolation of magnetic polarons (MPs), acting as "spacers" between MPs. We propose that such "spacers", being in fact volumes incompatible with existence of MPs, may be responsible for the decrease of the percolation temperature and for the additional (magneto)resistivity increase in systems with MPs.

cond-mat.mtrl-sci↗

arXiv2006

Anomalous charge transport in dodecaborides RB12 (R- Ho, Er, Tm, Lu)

High precision measurements of Hall RH(T) and Seebeck S(T) coefficients have been carried out for the first time on single crystals of rare earth dodecaborides RB12 (R - Ho, Er, Tm, Lu) at temperatures 1.8 - 300K. Low temperature anomalies associated with antiferromagnetic phase transitions in HoB12, ErB12 and TmB12 compounds have been detected on the temperature dependencies of RH(T) and S(T). The estimated values of charge carriers mobility allowed us to conclude about the appreciable influence of spin fluctuations on the charge transport in these compounds with B12 atomic clusters.

cond-mat.str-el↗

arXiv2006

Neutron scattering on HoB$_{12}$ - short-range correlations above T$_{N}$

Neutron scattering experiments on frustrated fcc - antiferromagnet HoB$_{12}$ have been performed above T$_{N}$ = 7.4 K. Diffuse scattering patterns indicate that above Neel temperature correlations between neighboring magnetic moments of Ho - ions appear, similar to the appearance of coupled spin-pairs (dimers) in low dimensional magnets. Moreover, the diffuse patterns show a symmetry reduction from fcc to simple cubic. Analogous behavior in 3D systems is not known, although it was predicted by theory. The role of various interactions leading to this behavior is being analyzed and discussed.

cond-mat.str-el↗

arXiv2003

Nonlinear excitations in CsNiF3 in magnetic fields perpendicular to the easy plane

Experimental and numerical studies of the magnetic field dependence of the specific heat and magnetization of single crystals of CsNiF3 have been performed at 2.4 K, 2.9 K, and 4.2 K in magnetic fields up to 9 T oriented perpendicular to the easy plane. The experimental results confirm the presence of the theoretically predicted double peak structure in the specific heat arising from the formation of nonlinear spin modes. The demagnetizing effects are found to be negligible, and the overall agreement between the data and numerical predictions is better than reported for the case when the magnetic field was oriented in the easy plane. Demagnetizing effects might play a role in generating the difference observed between theory and experiment in previous work analyzing the excess specific heat using the sine-Gordon model.

cond-mat.soft↗

arXiv2001

The energy gap of intermediate-valent SmB6 studied by point-contact spectroscopy

We have investigated the intermediate valence narrow-gap semiconductor SmB6 at low temperatures using both conventional spear-anvil type point contacts as well as mechanically controllable break junctions. The zero-bias conductance varied between less than 0.01 mikrosiemens and up to 1 mS. The position of the spectral anomalies, which are related to the different activation energies and band gaps of SmB6, did not depend on the the contact size. Two different regimes of charge transport could be distinguished: Contacts with large zero - bias conductance are in the diffusive Maxwell regime. They had spectra with only small non-linearities. Contacts with small zero - bias conductance are in the tunnelling regime. They had larger anomalies, but still indicating a finite 45 % residual quasiparticle density of states at the Fermi level at low temperatures of T = 0.1 K. The density of states derived from the tunelling spectra can be decomposed into two energy-dependent parts with Eg = 21 meV and Ed = 4.5 meV wide gaps, respectively.

cond-mat.str-el↗