Structural transition in the magnetoelectricZnCr2Se4spinel under pressure

Abstract

Τhe magnetoelectric ZnCr 2 Se 4 spinel, with space group Fd3 m, undergoes a reversible first-order structural transition initiating at 17 GPa, as revealed by our highpressure X-ray diffraction studies at room temperature. We tentatively assign the high-pressure modification to a AMo 2 S 4 -type phase, a distorted variant of the monoclinic Cr 3 S 4 structure. Furthermore, our Raman investigation provides evidence for a pressure-induced insulator-metal transition. Our density functional theory calculations successfully reproduce the structural transition. They indicate significant band gap and magnetic moment reduction accompanying the pressure-induced structural modification. We discuss our findings in conjunction with the available high-pressure results on other Cr-based chalcogenide spinels.

Pressure-induced phase transitions in the CdCr2Se4 spinel

“…Upon increasing pressure, the Fd3 m Raman features could be followed up to 10 GPa. The respective Raman mode pressure coefficients and mode Grüneisen parameters γ i of CdCr 2 Se 4 are very similar to those of other Cr-based spinels [18][19][20] (Table I). We note that the Fd3 m γ i values have been calculated with the revised formula for polyatomic structures, as proposed by Hofmeister et al 58 .…”

“…A simple extrapolation of the existing curves yields zero E g values either at 80 GPa (dE g /dP = -0.0165 eV/GPa, AFM1) or 57 GPa (dE g /dP = -0.032 eV/GPa, AFM2). This electronic behavior is rather different compared to other Cr-spinels, where pressure-induced insulator-metal transitions at lower pressures are reported 18,21,24,25 .…”

“…Our XRD study points to structural disorder as the reason behind the vanishing of the Raman activity above 23 GPa, as we discuss below. Finally, the starting Fd3 m phase could be recovered upon decompression at ~9.5 GPa; the reversibility of the original structure seems to be another general feature of Cr-spinels [18][19][20] . Fig.…”

“…The straightforward effect of compression is the reduction of the Cr-Cr distances, which in turn causes the enhancement of the AFM J 1 interactions over the FM J 2 ones. Besides from tuning the magnetic interactions, pressure can also lead to structural [18][19][20][21][22][23] , electronic 21,24,25 , and even magnetic 21 27 . A red-shift of E g was detected below T C 27 , but without any apparent complementary structural effect 5,28 .…”

Colloidal synthesis and magnetic properties of anisotropic-shaped spinel CuCr2Se4 nanocrystals

“…As a remarkable class of magnetic materials with diverse electronic transport properties (metallic, semiconducting, and insulating), chromium-based chalcogenide spinels (chalcospinels) ACr 2 X 4 (A ¼ Cu, Cd, Hg, Fe, and Co; X ¼ S, Se, and Te) have gained signicant attention in recent years. [9][10][11][12] However, due to complications related to control of the oxidation state of chromium and the limited known nonvolatile chalcogen precursors for selective synthesis of the spinel phase, the exploration of novel routes for preparing Cr-based chalcospinel nanomaterials with desired morphology remains a challenge. 13 An important class of magnetic chalcospinels, CuCr 2 S 4 , CuCr 2 Se 4 , and CuCr 2 Te 4 , are ferromagnetic metals with Curie temperatures (T c ) of 377, 430, and 360 K, respectively, and are also metallic.…”