Academy of Sciences of Moldova

About: Academy of Sciences of Moldova is a government organization based out in Chisinau, Moldova. It is known for research contribution in the topics: Crystal structure & Hydrogen bond. The organization has 2039 authors who have published 3203 publications receiving 39566 citations. The organization is also known as: Academia de Științe a Moldovei & ASM.

Néel-type skyrmion lattice with confined orientation in the polar magnetic semiconductor GaV4S8.

Abstract: 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 Neel-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.

Relaxor ferroelectricity and colossal magnetocapacitive coupling in ferromagnetic CdCr2S4.

Abstract: Ferromagnets have been known since ancient times. Ferroelectrics were discovered 80 years ago, and both properties are important in many areas of technology and electronics. Materials displaying both ferroelectricity and ferromagnetism combine the potential applications of both parent phases, with a range of new applications in optics, electronic circuitry and multiple-state memory devices. Such materials are rare, but one described this week, the common sulpho-spinel CdCr2S4, shows promise. It combines reasonable ordering temperatures (the point at which magnetic properties disappear) with sizeable magnetization and polarization well suited for application. Materials in which magnetic and electric order coexist—termed ‘multiferroics’ or ‘magnetoelectrics’—have recently become the focus of much research1,2,3,4. In particular, the simultaneous occurrence of ferromagnetism and ferroelectricity, combined with an intimate coupling of magnetization and polarization via magnetocapacitive effects, holds promise for new generations of electronic devices. Here we present measurements on a simple cubic spinel compound with unusual, and potentially useful, magnetic and electric properties: it shows ferromagnetic order coexisting with relaxor ferroelectricity (a ferroelectric cluster state with a smeared-out phase transition), both having sizable ordering temperatures and moments. Close to the ferromagnetic ordering temperature, the magnetocapacitive coupling (characterized by a variation of the dielectric constant in an external magnetic field) reaches colossal values, approaching 500 per cent. 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 that drive the formation of the ferroelectric state.