arXiv subjects

Manuel Angst

Publications and source records attributed to Manuel Angst.

4 recordsLinked to original sources

arXiv2019

Growth of layered Lu$_2$Fe$_3$O$_7$ and Lu$_3$Fe$_4$O$_{10} $ single crystals exhibiting long-range charge order via the optical floating-zone method

We report the controlled growth of single crystals of intercalated layered Lu$ _{1+n} $Fe$ _{2+n} $O$ _{4+3n-\delta} $ ($ n $=1,2) with different oxygen stoichiometries ${\delta}$. For the first time crystals sufficiently stoichiometric to exhibit superstructure reflections in X-ray diffraction attributable to charge ordering were obtained. The estimated correlation lengths tend to be smaller than for not intercalated LuFe$ _2 $O$ _4$. For Lu$ _2 $Fe$ _3 $O$ _7 $, two different superstructures were observed, one an incommensurate zigzag pattern similar to previous observations by electron diffraction, the other an apparently commensurate pattern with ($\frac{1}{3}\frac{1}{3}0$) propagation. Implications for the possible charge order in the bilayers are discussed. Magnetization measurements suggest reduced magnetic correlations and the absence of an antiferromagnetic phase.

cond-mat.str-el↗

arXiv2015

Stoichiometric YFe2O4-\delta\ single crystals grown by the optical floating zone method

We report the growth of YFe2O4-\delta\ single crystals by the optical floating zone method, showing for the first time the same magnetization as highly stoichiometric (\delta = 0.00) powder samples and sharp superstructure reflections in single crystal x-ray diffraction. The latter can be attributed to three dimensional long-range charge ordering. Resonant x-ray diffraction at the Fe K-edge with full linear polarization analysis was used for the investigation of the possibility of orbital order.

cond-mat.mtrl-sci↗

arXiv2013

Ferroelectricity from iron valence ordering in rare earth ferrites?

The possibility of multiferroicity arising from charge ordering in LuFe2O4 and structurally related rare earth ferrites is reviewed. Recent experimental work on macroscopic indications of ferroelectricity and microscopic determination of coupled spin and charge order indicates that this scenario does not hold. Understanding the origin of the experimentally observed charge and spin order will require further theoretical work. Other aspects of recent research in these materials, such as geometrical frustration effects, possible electric-field-induced transitions, or orbital order are also briefly treated.

cond-mat.str-el↗

arXiv2012

Dielectric properties of charge ordered LuFe2O4 revisited: The apparent influence of contacts

We show results of broadband dielectric measurements on the charge ordered, proposed to be mul- tiferroic material LuFe2O4. The temperature and frequency dependence of the complex permittivity as investigated for temperatures above and below the charge-oder transition near T_CO ~ 320 K and for frequencies up to 1 GHz can be well described by a standard equivalent-circuit model considering Maxwell-Wagner-type contacts and hopping induced AC-conductivity. No pronounced contribution of intrinsic dipolar polarization could be found and thus the ferroelectric character of the charge order in LuFe2O4 has to be questioned.

cond-mat.str-el↗