Following the early prediction of the skyrmion lattice (SkL)--a periodic array of spin vortices--it has been observed recently in various magnetic crystals mostly with chiral structure. Although non-chiral but polar crystals with Cnv symmetry were identified as ideal SkL hosts in pioneering theoretical studies, this archetype of SkL has remained experimentally unexplored. Here, we report the discovery of a SkL in the polar magnetic semiconductor GaV4S8 with rhombohedral (C3v) symmetry and easy axis anisotropy. The SkL exists over an unusually broad temperature range compared with other bulk crystals and the orientation of the vortices is not controlled by the external magnetic field, but instead confined to the magnetic easy axis. Supporting theory attributes these unique features to a new Néel-type of SkL describable as a superposition of spin cycloids in contrast to the Bloch-type SkL in chiral magnets described in terms of spin helices.

, which reveal magnetic and electric order, are in the focus of recent solid state research [1][2][3][4] . Especially the simultaneous occurrence of ferroelectricity and ferromagnetism, combined with an intimate coupling of magnetization and polarization via magneto-capacitive effects, could pave the way for a new generation of electronic devices. Here we present measurements on a simple cubic spinel with unusual properties: It shows ferromagnetic order and simultaneously relaxor ferroelectricity, i.e. a ferroelectric cluster state, reached by a smeared-out phase transition, both with sizable ordering temperatures and moments. Close to the ferromagnetic ordering temperature the magneto-capacitive coupling, characterized by a variation of the dielectric constant in an external magnetic field, reaches colossal values of nearly 500%. We attribute the relaxor properties to geometric frustration, which is well known for magnetic moments, but here is found to impede long-range order of the structural degrees of freedom.The coexistence of ferroelectricity and ferromagnetism would constitute a mile stone for modern electronics and functionalised materials. The most appealing applications are new types of storage media using both magnetic and electric polarization and the possibility of electrically reading/writing magnetic memory devices (and vice versa). However, it is clear now that ferroelectric ferromagnets are rare 5,6 and mostly exhibit rather weak ferromagnetism. Spinel compounds are an important class of materials and their electronic properties are in the focus of research since the famous work of Verwey on magnetite 7 . Recent reports on geometrical frustration of the spin and orbital degrees of freedom 8 , and the observation of an orbital-glass state 9 in sulpho spinels, demonstrate the rich and complex physics, characteristic of these compounds. Here we report on another interesting experimental observation in a spinel system: R elaxor ferroelectricity in ferromagnetic CdCr 2 S 4 and the occurrence of colossal magnetocapacitive effects.CdCr 2 S 4 crystallizes in the normal cubic spinel structure (space group Fd3m, a = 1.024 nm), with Cr 3+ octahedrally surrounded by sulphur ions, yielding a half-filled lower t 2g triplet with a spin S = 3/2. Ferromagnetism in CdCr 2 S 4 is well known 10 , but early experimental observations of a number of mysterious features have fallen into oblivion: For example, reports of an anomalous expansion coefficient at low temperatures 11,12 , an unexpected concomitant broadening of the d iffraction lines 11 , a strong blue shift of the absorption edge on passing the ferromagnetic phase transition 13 , the observation of anomalously large phonon shifts and damping effects close to T c 14 and the observation of large magneto-resistance effects 15 . Figure 1a shows the inverse magnetic susceptibility χ -1 and the low-temperature magnetization M. The straight line indicates a fit to the paramagnetic susceptibility, which results in a Curie-Weiss temperature of 155 K and a paramagneti...

A zoo of multiferroic phases shows up in the lacunar spinel GaV4S8, including skyrmions carrying ferroelectric polarization.