| Summary: | 碩士 === 國立中山大學 === 物理學系研究所 === 103 === Chiral magnetic lattice shows exotic physical properties such as spin ice/spin liquid order, topological insulators, magneto-electric coupling, and so on. Essentially, all these fascinating phenomena have strongly related to their peculiar spin arrangement, i.e. spiral, conical and helical. The chiral magnetic lattice of Cu2OSeO3 exhibit such kind of unique magnetic ordering where spins configured into a vortex-like pattern called as skyrmion. Cu2OSeO3 exhibits ferrimagnetic ordering around 56 K. Below magnetic ordering, under moderate magnetic field the spin orientation transfer from helical to conical phase via intermediate skyrmions phase. In this thesis, we study the influence of isovalent doping on the Skyrmion phase of Cu2OSeO3.
The polycrystalline (Cu1-XNiX)2OSeO3 (x = 0.0 to 0.1) samples were prepared by standard solid-state method. Temperature (T) and field (H) dependent AC susceptibility (ac) technique was employed to study the H-T phase diagram. From ac vs. T measurement, we found the transition temperature (TC) shifts to low temperature as the Ni doping level increases. A second magnetic peak noticed below TC for doping concentration x > 0.03. Field dependent magnetization (M-H) curves indicate the nominal change of saturation magnetization, which hints the Ni randomly occupy the Cu(I) and Cu(II) positions. H-T phase diagram for all the samples constructed using the ac vs. H curves at the different temperatures. Several significant changes noticed from the H-T phase diagram. First, the conical phase boundary enhances from 806.22 Oe (x = 0) to 996.42 Oe (x = 0.1) at 45 K, whereas small decrease in helical boundary noticed with increase of Ni doping concentration. Interestingly, Ni doping strongly influence the skyrmion zone, the skyrmion zone systematically enhances with the doping concentration x = 0.06. For x ≥ 0.08, a split in the skyrmion zone has been noticed. Our detailed experimental results signifies that the magnetic ion doping in the Cu2OSeO3 strongly modulate the complex magnetic interaction of Cu(I) and Cu(II) that stabilize the skyrmion phase in wider temperature interval in the H-T phase diagram.
|
|---|
