Synaptic Behavior in Ferroelectric Epitaxial Rhombohedral Hf0.5Zr0.5O2 Thin Films

In this work, the switching mechanism of the rhombohedral phase of HZO films is characterized by a two-stage process. In addition, the synaptic behaviour of this phase is presented, comparing it with previous reports on orthorhombic or non-epitaxial films. Unexpected similarities have been found between these structurally distinct systems

Dataset: Spherulitic and rotational crystal growth of Quartz thin films

To obtain crystalline thin films of alpha-Quartz represents a challenge due to the tendency for the material towards spherulitic growth. Thus, understanding the mechanisms that give rise to spherulitic growth can help regulate the growth process. Here the spherulitic type of 2D crystal growth in thin amorphous Quartz films was analyzed by electron back-scatter diffraction (EBSD). EBSD was used to measure the size, orientation, and rotation of crystallographic grains in polycrystalline SiO2 and GeO2 thin films with high spatial resolution. Individual spherulitic Quartz crystal colonies contain primary and secondary single crystal fibers, which grow radially from the colony center towards its edge, and fill a near circular crystalline area completely. During their growth, individual fibers form so-called rotational crystals, when some lattice planes are continuously bent. The directions of the lattice rotation axes in the fibers were determined by an enhanced analysis of EBSD data. A possible mechanism, including the generation of the particular type of dislocation(s), is suggested

Antiferromagnetic ordering and uncoupled spins in CaFe2O4 thin films probed by spin Hall-magnetoresistance measurements

CaFe2O4 is a uniaxial antiferromagnet displaying two coexisting magnetic orderings, A and B, characterized by up-down-up-down and up-up-down-down spin modulation, respectively, and the emergence of a net magnetization in a limited temperature range, which is not yet understood. We investigate the angular dependent magnetoresistance (ADMR) at the interface between Pt and CaFe2O4 and exploit the crystallographic domain structure of thin film samples to probe the spin Hall magnetoresistance (SMR) at a single- and multi-domain scale. Upon rotation of the magnetic field along three orthogonal planes, we observe a sinusoidal modulation of the magnetoresistance indicating that the mechanism for SMR is the rotation of the spins, despite the strong magnetocrystalline and shape anisotropies. This, together with the study of the magnetic field dependence of the response, allows us to extract two contributions to the SMR: one corresponds to the long-range antiferromagnetic ordering, supporting a single ground state scenario. The second contribution originates from uncompensated and uncoupled spins. These are expected to exist at the antiphase boundaries between antiferromagnetic domains. Here we show that these are uncoupled from the antiferromagnetic ordering. Nonetheless, the long range correlations that emerge in the proximity of the critical antiferromagnetic transition could give rise to ordering of the uncompensated spins and be responsible for the net magnetization observed in this antiferromagnet

Phenomenological classification of metals based on resistivity

Efforts to understand metallic behavior have led to important concepts such as those of strange metals, bad metals, or Planckian metals. However, a unified description of metallic resistivity is still missing. An empirical analysis of a large variety of metals shows that the parallel resistor formalism used in the cuprates, which includes T-linear and T-quadratic dependence of the electron scattering rates, can be used to provide a phenomenological description of the electrical resistivity in all metals. Here, we show that the different metallic classes are then determined by the relative magnitude of these two components and the magnitude of the extrapolated residual resistivity. These two parameters allow us to categorize a few systems that are notoriously hard to ascribe to one of the currently accepted metallic classes

CSD 2041937: Experimental Crystal Structure Determination

Related Article: Liliia D. Kulish, Pavan Nukala, Rick Scholtens, A. G. Mike Uiterwijk, Ruben Hamming-Green, Graeme R. Blake|2021|J.Mater.Chem.C|9|1370|doi:10.1039/D0TC05396

Dataset: Reversible oxygen migration and phase transitions in hafnia-based ferroelectric devices

Unconventional ferroelectricity, robust at reduced nanoscale sizes, exhibited by hafnia-based thin-films presents tremendous opportunities in nanoelectronics. However, the exact nature of polarization switching remains controversial. Here, we investigate epitaxial Hf0.5Zr0.5O2(HZO) capacitors, interfaced with oxygen conducting metals (La0.67Sr0.33MnO3, LSMO) as electrodes, using atomic resolution electron microscopy while in situelectrical biasing. By direct oxygen imaging, we observe reversible oxygen vacancy migration from the bottom to the top electrode through HZO and reveal associated reversible structural phase transitions in the epitaxial LSMO and HZO layers. We follow the phase transition pathways at the atomic scale and identify that these mechanisms are at play both in tunnel junctions and ferroelectric capacitors switched with sub-millisecond pulses. Our results unmistakably demonstrate that oxygen voltammetry and polarization switching are intertwined in these materials