H-induced stair-like metamagnetic transitions, large magnetocaloric and magnetoelectric effects related to the 4f electrons of rare-earth ions were revealed in chromite crystals.

Thermal transport of quantum magnets has elucidated the nature of low energy elementary excitations and complex interplay between those excited states via strong scattering of thermal carriers. BiCu2PO6 is a unique frustrated spin-ladder compound exhibiting highly anisotropic spin excitations that contain both itinerant and localized dispersion characters along the b- and a-axes respectively. Here, we investigate thermal conductivity κ of BiCu2PO6 under high magnetic fields (H) of up to 30 tesla. A dip-feature in κ, located at ~15 K at zero-H along all crystallographic directions, moves gradually toward lower temperature (T) with increasing H, thus resulting in giant suppression by a factor of ~30 near the critical magnetic field of Hc ≅ 23.5 tesla. The giant H- and T-dependent suppression of κ can be explained by the combined result of resonant scattering of phononic heat carriers with magnetic energy levels and increased phonon scattering due to enhanced spin fluctuation at Hc, unequivocally revealing the existence of strong spin-phonon coupling. Moreover, we find an experimental indication that the remaining magnetic heat transport along the b-axis becomes almost gapless at the magnetic quantum critical point realized at Hc.

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We report the effects of hydrostatic pressure up to p ∼ 1.73 GPa on the multiferroic and magnetoelectric properties of GdMn2O5 single crystals. The ferroelectric (FE) polarization can be enhanced at low pressures, while it decreased after reaching a maximum at p ∼ 1.30 GPa. This pressure induced variation of polarization can be ascribed to the combined results of Mn–Mn and Gd–Mn exchange striction under pressure. Our results show that the polarization induced by Mn–Mn interaction increases monotonously with increasing pressure and finally saturates above p ≳ 1.30 GPa. Interestingly, we find that a new FE phase appears in the temperature range of 31 K–38 K with pressure p ≳ 0.88 GPa. This new FE phase can be suppressed by magnetic field, but stabilized by pressure. The pressure-temperature (p–T) phase diagram of GdMn2O5 was obtained. Our analyses suggest that the pressure-induced new FE phase could arise from a non-collinear, incommensurate magnetic structure.