Magnetic and transport properties of the layered perovskite systemSr2−yYyCoO4

Abstract

Layered perovskite cobalt oxides 0.1, 0.3, 0.5, 0.67, 0.83 Layered perovskite cobalt oxides Sr 2−y Y y CoO 4 ͑y = 0, 0.1, 0.3, 0.5, 0.67, 0.83, and 1͒ were synthesized under high pressure and high temperature conditions. Structure refinement revealed that these compounds crystallize in K 2 NiF 4 -type structures with space group I4 / mmm. The parent compound Sr 2 CoO 4 undergoes a ferromagnetic transition with T c = 255 K. The T c decreases with increasing y to 150 K for y = 0.5, and ferromagnetism was not observed for y ജ 0.67. Assessment of spin states for Co 3+ and Co 4+ ions suggested strongly that both are present as intermediate spin states when y ഛ 0.67 at least for the higher temperature range above T c . Fairly large negative magnetoresistance was observed for Sr 2 CoO 4 in the vicinity of T c and in the lower temperature region.

Spin-orbit-induced exotic insulators in a three-orbital Hubbard model with(t2g)5electrons

“…In these materials, along with moderate electron correlations [6,7], there exists a strong relativistic spin-orbit coupling (SOC), which splits t 2g orbitals, already separated from e g orbitals due to a large crystal field, into the effective total angular momentum j = 1/2 doublet and j = 3/2 quartet orbitals in the atomic limit [8]. Since there are nominally five 5d electrons per Ir ion, the j = 1/2 orbital is half filled while the j = 3/2 orbitals are fully occupied.As opposed to simple expectation from strongly correlated 3d and 4d transition metal oxides [9][10][11][12][13], the experiments have revealed that the ground state of these Ir oxides is a j = 1/2 antiferromagnetic (AF) insulator [14][15][16][17]. The theoretical understanding of the j = 1/2 AF insulator has been also reported [14,[18][19][20][21][22][23][24].…”

“…As opposed to simple expectation from strongly correlated 3d and 4d transition metal oxides [9][10][11][12][13], the experiments have revealed that the ground state of these Ir oxides is a j = 1/2 antiferromagnetic (AF) insulator [14][15][16][17]. The theoretical understanding of the j = 1/2 AF insulator has been also reported [14,[18][19][20][21][22][23][24].…”

Band structures, magnetic properties, and enhanced magnetoresistance in the high pressure phase of Gd and Y doped two-dimensional perovskite Sr2CoO4 compounds

“…11 Very recently, metallic ferromagnetism with a Curie temperature T C of 250-255 K has been discovered in the K 2 NiF 4 -type two-dimensional layered perovskite Sr 2 CoO 4 in the form of both single crystalline films fabricated by pulsed laser deposition 12 ͑PLD͒ and bulks produced by a high pressure and high temperature technique. 13 A metal insulator transition with large negative MR values was observed in the vicinity of T C . The MR increases at low temperatures and reaches a maximum at the coercive field H c .…”

“…12,13 Y 3+ doping into Sr 2+ made the Sr 2 CoO 4 gradually change from a ferromagnetic metal to an antiferromagnetic semiconductor. 13 Band structure calculations by Lee and Pickett 14 revealed that the Sr 2 CoO 4 can be either a ferromagnetic metal for the thin film samples or a half metal for the high pressure phase samples. They pointed out that the newly discovered Sr 2 CoO 4 in the form of bulks fabricated by the high pressure technique and thin films made by PLD introduces new transition metal oxide physics and may be useful in spin electronics devices.…”

Simulation of Spin Transport Properties in Schottky Barrier FET Using Monte Carlo Method

“…So Schottky Barrier FET is a structure suitable for spin current injection. Some research groups have simulated this structure by Monte Carlo Method [4,5]. However, scatterings which are of great importance have not been fully considered.…”