We have synthesised and characterised a novel organic–inorganic hybrid crystal, [(CH₃)₂NH₂]₂KCr(CN)₆. The thermal DSC, TMA, DTG and DTA analyses indicate two solid-to-solid structural phase transitions (PTs). According to the X-ray diffraction experiments, the first PT at 220 K is isostructural, since it does not involve a change of the space group. This transition occurs between the states, where the (CH₃)₂NH₂ ⁺ cations are orientationally disordered and ordered (frozen). The other reversible PT at 481 K leads to a melt-like phase similar to the one observed in plastic crystals or polar liquids. Dielectric spectroscopy has been used to characterise the switching properties of the dipole moments in the vicinity of the PTs. Continuous-wave electron paramagnetic resonance spectroscopy was employed to investigate the effect of ordering on the local environment of the Cr³⁺ ions. We have also applied the quasielastic neutron scattering (QENS) technique as well as ¹H NMR spectroscopy to measure the dynamics of the (CH₃)₂NH₂ ⁺ cations residing in the inorganic framework.

Perovskite-like [TPrA][Cd(dca)₃] undergoes four temperature-induced phase transitions associated with dielectric anomalies and one pressure-induced phase transition into a monoclinic phase.

At low temperature, methyl groups act as hindered quantum rotors exhibiting rotational quantum tunneling, which is highly sensitive to a local methyl group environment. Recently, we observed this effect using pulsed electron paramagnetic resonance (EPR) in two dimethylammonium-containing hybrid perovskites doped with paramagnetic Mn²⁺ ions. Here, we investigate the feasibility of using an alternative fast-relaxing Co²⁺ paramagnetic center to study the methyl group tunneling, and, as a model compound, we use dimethylammonium zinc formate [(CH₃)₂NH₂][Zn(HCOO)₃] hybrid perovskite. Our multifrequency (X-, Q- and W-band) EPR experiments reveal a high-spin state of the incorporated Co²⁺ center, which exhibits fast spin-lattice relaxation and electron spin decoherence. Our pulsed EPR experiments reveal magnetic field independent electron spin echo envelope modulation (ESEEM) signals, which are assigned to the methyl group tunneling. We use density operator simulations to extract the tunnel frequency of 1.84 MHz from the experimental data, which is then used to calculate the rotational barrier of the methyl groups. We compare our results with the previously reported Mn²⁺ case showing that our approach can detect very small changes in the local methyl group environment in hybrid perovskites and related materials.

Following the success of cryogenic EPR signal preamplification at X-band, we present a Q-band EPR cryoprobe compatible with a standard EPR resonator. The probehead is equipped with a cryogenic ultra low-noise microwave amplifier and its protection circuit that are placed close to the sample in the same cryostat. Our cryoprobe maintains the same functionality and compatibility as the commercial instrument allowing high-power pulsed EPR experiments of typical samples. The performance of our setup is benchmarked using pulsed EPR and ENDOR experiments revealing a significant sensitivity improvement, which reduces the measurement time by a factor of about 40x at low temperature.

Electron paramagnetic resonance (EPR) spectroscopy is a broadly used technique to study paramagnetic centers in diverse fields ranging from biology to quantum technologies. The availability of well-established commercial instrumentation, including features such as rapid sample exchange, has been a key enabler for EPR to be applied widely across disciplines. Here, we present a three-order-of-magnitude increase in the spin number sensitivity of the commonly used X-band pulsed EPR while retaining full compatibility with conventional instrumentation and typical sample conditions. Our approach employs planar spiral-shaped microresonators with 7 nL mode volumes fabricated from yttrium barium copper oxide (YBCO) high-temperature superconductor. We achieve a wide range of microwave coupling by a single microresonator inside a conventional EPR tube, loaded into an EPR cavity. The performance of the spiral microresonators is demonstrated through a suite of pulsed EPR experiments on standard samples including dipolar and hyperfine spectroscopies. By placing a sample within a microfluidic microstructure fabricated to match the mode profile of the microresonator, we obtain a high-fidelity spin control with a spin-number sensitivity of 10^7 spins/G/Hz^1/2. Our approach significantly advances the applicability of superconducting microresonators as versatile and readily applicable tools for high sensitivity EPR.

The S100 family consists of calcium binding proteins that are largely known for their contribution to the neuroinflammatory processes. They are associated with various cardiac and neurological functions as well as related diseases. A few S100 proteins can form unspecific or amyloid aggregates in neuropathologies and thus play a part in dementia pathogenesis. Among all S100 proteins, S100B and S100A9 aggregation properties are the most investigated, however, there is a lack of studies regarding other S100 members. In particular, S100A1 and S100A8 are also associated with neuropathies, but their interactions or aggregation are poorly understood. Therefore, in this study, we explored whether S100A1 and S100A8 proteins can form heterodimers, interact or co-aggregate. Our results revealed that S100A1 and S100A8 interactions and amyloid aggregation are driven by calcium ions. We observed that while S100A1 remains mostly stable, S100A8 forms various types of spherical or unspecific aggregates. While they do not form stable heterodimers like calprotectin, their transient interactions facilitate the formation of worm-like amyloid fibrils and the process is regulated by different calcium ion concentrations. At calcium ions saturation, both proteins are stabilized leading to inhibition of aggregation. Overall, by employing a diverse range of techniques from amyloid and protein-specific fluorescence detection to electron-electron double resonance spectroscopy, we elucidated interactions between S100 proteins that might otherwise be overlooked, enhancing our understanding of their aggregation behaviour.