Neutron scattering studies on stripe phases in non-cuprate materials

Abstract

Several non-cuprates layered transition-metal oxides exhibit clear evidence for stripe ordering of charges and magnetic moments. Therefore, stripe order should be considered as the typical consequence of doping a Mott insulator, but only in cuprates stripe order or fluctuating stripes coexist with metallic properties. A linear relationship between the charge concentration and the incommensurate structural and magnetic modulations can be considered as the finger print of stripe ordering with localized degrees of freedom. In nickelates and in cobaltates with K 2 NiF 4 structure, doping suppresses the nearest-neighbor antiferromagnetism and induces stripe order. The higher amount of doping needed to induce stripe phases in these non-cuprates series can be attributed to reduced charge mobility. Also manganites exhibit clear evidence for stripe phases with further enhanced complexity, because orbital degrees of freedom are involved. Orbital ordering is the key element of stripe order in manganites since it is associated with the strongest structural distortion and with the perfectly fulfilled relation between doping and incommensurability. Magnetic excitations in insulating stripe phases exhibit strong similarity with those in the cuprates, but only for sufficiently short magnetic correlation lengths reflecting well-defined magnetic stripes that are only loosely coupled.

Magnetic phase diagram ofLa2−xSrxCoO4revised using muon-spin relaxation

“…The rapid suppression of T N with increasing x in lightly doped samples is reminiscent of La 2−x Sr x CuO 4 and other cuprates, where local probe measurements also reveal a continuous spin-freezing transition at temperatures well below that of magnetic ordering [45][46][47][48]. Our results indicate that the behavior associated with region II extends over a broad range of x, implying that the phase diagram bears a greater similarity to that of La 2−x Sr x NiO 4 [6,[49][50][51][52]. However, the stripe phase in the nickelate system is of a very different character, since the charge stripes themselves remain magnetically active [53].…”

“…Although a detailed comparison of specific systems has been found to be problematical, in order to elucidate the details of the physics at play in a different context it is illuminating to study isostructural nonsuperconducting 3d transition metal oxides [6] such as the antiferromagnetic series La 2−x Sr x CoO 4 (LSCO). Controlled doping of holes into the two-dimensional CoO 2 layers is achieved via substitution of Sr for La but, in contrast to the cuprates, a spin-blockade mechanism means the series remains an insulator for x 1 [7].…”

Evidence for Short-Range-Ordered Charge Stripes Far above the Charge-Ordering Transition inLa1.67Sr0.33NiO4

“…In addition, we identify a contribution to the mean-square displacements of Ni and in-plane O atoms whose width correlates quite well with the size of the pseudogap extracted from the reported optical conductivity, with a non-Debye-like component that persists below and well above TCO. We infer that dynamic chargestripe correlations survive to T ∼ 2TCO La 2−x Sr x NiO 4 has served as a model system for studying stripe order [21]. Charge-stripe order can occur at relatively high temperatures, reaching a maximum of T CO = 240 K at x = 1 3 [22,23].…”

“…La 2−x Sr x NiO 4 has served as a model system for studying stripe order [21]. Charge-stripe order can occur at relatively high temperatures, reaching a maximum of T CO = 240 K at x = 1 3 [22,23].…”

Stacked charge stripes in the quasi-2D trilayer nickelate La 4 Ni 3 O 8

“…Many mixed valent TMOs adopt insulating "charge ordered" states, in which an inhomogeneous but long-range ordered configuration of the charge density condenses from a uniform metallic state (5). The real space pattern of charge order varies by material (6)(7)(8)(9), but a typically observed motif is some variety of charge stripes. Such stripes have been observed in cobaltites (10)(11)(12), cuprates (13)(14)(15), nickelates (16)(17)(18)(19), and manganites (20)(21)(22), albeit with highly materials-dependent configurations that hinge on a balance among Coulomb, lattice, and magnetic exchange energies.…”