New sustainable ternary copper phosphide thermoelectrics

Funding: R. J. Q. and J.-W. G. B. acknowledge the Leverhulme Trust (RPG-2020-177). A. D. H. acknowledges the EPSRC (EP/ R013004/1).The thermoelectric performance of ACuP (A = Mg and Ca) with abundant elements and low gravimetric density is reported. Both systems are p-type doped by intrinsic Cu vacancy defects, have large power factors and promising figures of merit, reaching zT = 0.5 at 800 K. This demonstrates that copper phosphides are a potential new class of thermoelectric materials for waste heat harvesting.Publisher PDFPeer reviewe

A field induced modulated state in the ferromagnet PrPtAl

The theory of quantum order-by-disorder (QOBD) explains the formation of modulated magnetic states at the boundary between ferromagnetism and paramagnetism in zero field. PrPtAl has been argued to provide an archetype for this. Here, we report the phase diagram in magnetic field, applied along both the easy a axis and hard b axis. For field aligned to the b axis, we find that the magnetic transition temperatures are suppressed and at low temperature there is a single modulated fan state, separating an easy a axis ferromagnetic state from a field polarized state. This fan state is well explained with the QOBD theory in the presence of anisotropy and field. Experimental evidence supporting the QOBD explanation is provided by the large increase in the T^{2} coefficient of the resistivity and direct detection of enhanced magnetic fluctuations with inelastic neutron scattering, across the field range spanned by the fan state. This shows that the QOBD mechanism can explain field induced modulated states that persist to very low temperature

Potential room-temperature multiferroicity in cupric oxide under high pressure

International audienceCuO, known to be multiferroic (MF) from T-L = 213 K to T-N = 230 K at ambient pressure, has been the subject of debates about its ability to exhibit multiferroicity at room temperature (RT) under high hydrostatic pressure. Here we address this question based on theoretical and experimental investigations. The influence of hydrostatic pressure on T-L and T-N has been estimated from ab initio calculations combined with classical Monte-Carlo simulations and a quasi-1D antiferromagnetic analytical model. From the experimental side, electric permittivity anomalies related to ferroelectric transitions have been followed with dielectric measurements on single crystals up to 6.1 GPa. We show that the temperature T-N below which the MF state forms increases with pressure linearly to higher pressure that hitherto supposed, and indeed based on our calculations, should exceed RT above about 20 GPa