Metals cannot exhibit ferroelectricity because static internal electric fields are screened by conduction electrons¹, but in 1965, Anderson and Blount predicted the possibility of a ferroelectric metal, in which a ferroelectric-like structural transition occurs in the metallic state². Up to now, no clear example of such a material has been identified. Here we report on a centrosymmetric () to non-centrosymmetric (R3c) transition in metallic LiOsO₃ that is structurally equivalent to the ferroelectric transition of LiNbO₃ (ref. 3). The transition involves a continuous shift in the mean position of Li⁺ ions on cooling below 140 K. Its discovery realizes the scenario described in ref. 2, and establishes a new class of materials whose properties may differ from those of normal metals.

In rhombohedral CaMn7O12, an improper ferroelectric polarization of magnitude 2870\,\,$\mu${}C\,m-2 is induced by an incommensurate helical magnetic structure that evolves below TN1=90\,\,K. The electric polarization was found to be constrained to the high symmetry threefold rotation axis of the crystal structure, perpendicular to the in-plane rotation of the magnetic moments. The multiferroicity is explained by the ferroaxial coupling mechanism, which in CaMn7O12 gives rise to the largest magnetically induced, electric polarization measured to date.

A theory of superconductivity in the iron-based materials requires an understanding of the phase diagram of the normal state. In these compounds, superconductivity emerges when stripe spin density wave (SDW) order is suppressed by doping, pressure or atomic disorder. This magnetic order is often pre-empted by nematic order, whose origin is yet to be resolved. One scenario is that nematic order is driven by orbital ordering of the iron 3d electrons that triggers stripe SDW order. Another is that magnetic interactions produce a spin-nematic phase, which then induces orbital order. Here we report the observation by neutron powder diffraction of an additional fourfold-symmetric phase in Ba_1−xNa_xFe₂As₂ close to the suppression of SDW order, which is consistent with the predictions of magnetically driven models of nematic order.

We report the results of a systematic investigation of the phase diagram of the iron-based superconductor Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ from $x$ $=$ 0 to $x$ $=$ 1.0 using high-resolution neutron and x-ray diffraction and magnetization measurements. The polycrystalline samples were prepared with an estimated compositional variation of $\Delta x$ $\lesssim$ 0.01, allowing a more precise estimate of the phase boundaries than reported so far. At room temperature, Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ crystallizes in a tetragonal structure with the space group symmetry of $I$4/mmm, but at low doping, the samples undergo a coincident first-order structural and magnetic phase transition to an orthorhombic (O) structure with the space group Fmmm and a striped antiferromagnet (AF) with the space group $F_{\mathrm{c}}mm$′$m$′. The transition temperature falls from a maximum of 139 K in the undoped compound to 0 K at $x$ $=$ 0.252, with a critical exponent as a function of doping of 0.25(2) and 0.12(1) for the structural and magnetic order parameters, respectively. The onset of superconductivity occurs at a critical concentration of $x$ $=$ 0.130(3), and the superconducting transition temperature grows linearly with $x$ until it crosses the AF/O phase boundary. Below this concentration, there is microscopic phase coexistence of the AF/O and superconducting order parameters, although a slight suppression of the AF/O order is evidence that the phases are competing. At higher doping, superconductivity has a maximum $T_{\mathrm{c}}$ of 38 K at $x$ $=$ 0.4 that falls to 3 K at $x$ $=$ 1.0. We discuss reasons for the suppression of the spin density wave order and the electron–hole asymmetry in the phase diagram.

Recent studies have demonstrated the potential of antiferromagnets as the active component in spintronic devices. This is in contrast to their current passive role as pinning layers in hard disk read heads and magnetic memories. Here we report the epitaxial growth of a new high-temperature antiferromagnetic material, tetragonal CuMnAs, which exhibits excellent crystal quality, chemical order and compatibility with existing semiconductor technologies. We demonstrate its growth on the III–V semiconductors GaAs and GaP, and show that the structure is also lattice matched to Si. Neutron diffraction shows collinear antiferromagnetic order with a high Néel temperature. Combined with our demonstration of room-temperature-exchange coupling in a CuMnAs/Fe bilayer, we conclude that tetragonal CuMnAs films are suitable candidate materials for antiferromagnetic spintronics.

Magnetization measurements of a ${\mathrm{Gd}}_{0.5}{\mathrm{Ba}}_{0.5}{\mathrm{CoO}}_3$ perovskitelike compound have revealed an anomalous behavior at $T_i=240\mathrm{}\mathrm{K}$ and $T_C=277\mathrm{}\mathrm{K}$ that corresponds to appearing and disappearing spontaneous magnetization. The transition at $T_i$ is accompanied by the jump of conductivity and a giant magnetoresistance. Below $T_i$, ${\mathrm{Gd}}_{0.5}{\mathrm{Ba}}_{0.5}{\mathrm{CoO}}_3$ exhibits metamagnetic behavior. At about $T_M=370\mathrm{}\mathrm{K}$, a transition from a semiconductive to a quasimetallic state has been observed. It is supposed that a ferromagnetic low-spin cobalt state occurs in the temperature range between $T_i$ and $T_C$.