Spin crossover transition driven by pressure: Barocaloric applications

This article describes a mean-field theoretical model for Spin-Crossover (SCO) materials and explores its implications. It is based on a simple Hamiltonian that yields the high spin molar fraction as a function of temperature and pressure, as well as a temperature-pressure phase diagram for the SCO transition. In order to test the model, we apply it to the giant Barocaloric Effect (BCE) of the SCO material [FeL$_2$][BF$_4$]$_2$ and comprehensively analyse its behavior. We found that optical phonons are responsible for 92\% of the total barocaloric entropy change. DFT calculations show that these optical phonons are mainly assigned to the low frequencies modes of vibration ($<400$ cm$^{-1}$), being associated to the Fe coordination.Comment: 6 figure

Dynamical amplification of magnetoresistances and Hall currents up to the THz regime

Spin-orbit-related effects offer a highly promising route for reading and writing information in magnetic units of future devices. These phenomena rely not only on the static magnetization orientation but also on its dynamics to achieve fast switchings that can reach the THz range. In this work, we consider Co/Pt and Fe/W bilayers to show that accounting for the phase difference between different processes is crucial to the correct description of the dynamical currents. By tuning each system towards its ferromagnetic resonance, we reveal that dynamical spin Hall angles can non-trivially change sign and be boosted by over 500%, reaching giant values. We demonstrate that charge and spin pumping mechanisms can greatly magnify or dwindle the currents flowing through the system, influencing all kinds of magnetoresistive and Hall effects, thus impacting also dc and second harmonic experimental measurements.Comment: 19 pages, 4 figures, Supplementary Informatio

Incommensurate Spiral Spin Order in CaMn2_2Bi2_2 observed via High Pressure Neutron Diffraction

High pressure neutron diffraction is employed to investigate the magnetic behavior of CaMn$_2$Bi$_2$ in extreme conditions. In contrast to antiferromagnetic ordering on Mn atoms reported at ambient pressure, our results reveal that at high pressure, incommensurate spiral spin order emerges due to the interplay between magnetism on the Mn atoms and strong spin-orbit coupling on the Bi atoms: sinusoidal spin order is observed at pressures as high as 7.4 GPa. Competing antiferromagnetic order is observed at different temperatures in the partially frustrated lattice. This research provides a unique toolbox for conducting experimental magnetic and spin dynamics studies on magnetic quantum materials via high pressure neutron diffraction

Origin of anomalous breakdown of Bloch's rule in the Mott-Hubbard insulator MnTe2_2

We reinvestigate the pressure dependence of the crystal structure and antiferromagnetic phase transition in MnTe$_2$ by the rigorous and reliable tool of high pressure neutron powder diffraction. First-principles density functional theory calculations are carried out in order to gain microscopic insight. The measured N\'eel temperature of MnTe$_2$ is found to show unusually large pressure dependence of $12$ K GPa$^{-1}$. This gives rise to large violation of Bloch's rule given by $\alpha=\frac{d\log T_N}{d\log V}=-\frac{10}{3} \approx -3.3$, to a $\alpha$ value of -6.0 $\pm$ 0.1 for MnTe$_2$. The ab-initio calculation of the electronic structure and the magnetic exchange interactions in MnTe$_2$, for the measured crystal structures at different pressures, gives the pressure dependence of the Ne\'el temperature, $\alpha$ to be -5.61, in close agreement with experimental finding. The microscopic origin of this behavior turns to be dictated by the distance dependence of the cation-anion hopping interaction strength

Fósseis pleistocênicos de Scelidodon (Mylodontidae) e Tapirus (Tapiridae) em cavernas paranaenses (PR, sul do Brasil)

Notifica-se a primeira ocorrência de Scelidodon e Tapirus para a mastofauna pleistocênica paranaense. O material é procedente de cavernas calcárias da localidade de Gramados, Município de Cerro Azul, Estado do Paraná, Brasil. O gênero Scelidodon foi reconhecido por um fragmento do dentário esquerdo onde está inserida a série molariforme completa. O gênero Tapirus está representado por um fragmento do dentário direito, no qual está implantado o M3. Estas ocorrências ampliam a lista de fauna para o Estado do Paraná, além de expandir a distribuição geográfica destes gêneros no Brasil. ABSTRACT Two Pleistocene mammals, Scelidodon and Tapirus, are reported at Paraná State, Southern Brazil for the first time. The specimens were obtained from calcareous caves located at Gramados, Cerro Azul City. The Scelidodon sp. is represented by a fragment of the middle portion of the left dentary with a complete molariform teeth series, and Tapirus sp. is represented by a fragment of the right dentary in which M3 is found inserted. These occurrences enlarge the Paraná paleomastofauna list and the brazilian geographical distribution of these genera. RÉSUMÉ Ce travail rapport la première occurrence, pour letat du Paraná, sud du Brésil, de deux mammifères du pléistocène, Scelidodon et Tapirus. Les exemplaires provienent des cavernes calcaires de Gramados, à la ville de Cerro Azul. Le genre Scelidodon est représenté par un fragment du dentaire gauche oú est implanté la serie complète des molaires. Le genre Tapirus est représenté par un fragment du dentaire droite oú est implanté le M3. Ces occurrences amplifient la liste de la faune de letat du Paraná, au-delà détendre la distribution geographique de ces genres

Taxonomic revision and molecular phylogeny of Pisa (Decapoda: Majoidea: Epialtidae), including the description of a new genus of Pisinae.

CC BYThe spider crabs of the genus Pisa Leach, 1814 (Epialtidae: Pisinae) are reviewed in this study based on mor- phological and molecular data (16S and COI genes). From these results, a new genus, Afropisa n. gen., is established for the clade composed of Pisa carinimana Miers, 1879, Pisa calva Forest and Guinot, 1966 and Pisa sanctaehelenae Chace, 1966 based on carapace morphology, rostrum, pterygostomian tubercles and male gonopod 1. Additionally, Lissa chiragra (Fabricius, 1775) is transferred to Pisa based on morphological (adults and larvae) and molecular evidence. Furthermore, the status of Pisa hirticornis (Herbst, 1804) is discussed and clarified. The phylogenetic relationships between several Pis- inae Dana, 1851 genera, as revealed by molecular data, are discussed. An illustrated identification key of eastern Atlantic and Mediterranean species of Pisinae is provided