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Title: Magnetic anisotropy of CoS2 measured by torque magnetometer
Magnetic anisotropy is defined as the magnetization tendency of a magnetic material in a particular crystallographic direction. It has a significant impact when it comes to quantum materials research and industrial field applications like information storage devices. The magnetic anisotropy is mainly controlled by complicated interactions at the microscopic level. We studied the magnetic anisotropy of pure CoS2 single crystal, besides the effect of crystal structure and low doping concentrations on it. Torque magnetometry was utilized to determine the crystals' magnetocrystalline anisotropy. The angle dependence of torque τ(θ) for pure CoS2 was measured in a wide range of temperatures above and below the ferromagnetic order transition Tc, under the magnetic field; the angle θ is the orientation of the applied field with respect to the crystals’ c-axis. τ(θ) fitting was done to extract the amplitudes of higher-order corrections An using the following equation τ= A_n sin"(n θ" ) where n = 2, 4, 6 … To verify the effect of surface morphology on magnetic properties, τ (θ) of uncleaved and cleaved pure CoS2 was compared. The dominance of the two-fold symmetry was observed equally. Field-dependent torque τ(H) at different orientations was examined. It has been reported that the metamagnetic phase emerges while applying external pressure or by doping specific concentrations of Se or Ni. Accordingly, the effect of low concentration doping of Ni and Fe in CoS2 cleaved and un-cleaved samples, respectively, were examined. τ(θ) of Ni-doped CoS2 was found to have a relatively strong torque signal above Tc while maintaining two-fold symmetry. However, low concentrations of Fe-doped CoS2 had four-fold symmetry at low temperature, which turned into two-fold as the temperature increased. To figure out the peculiar behavior of Fe0.05Co0.95S2 more doping concentrations must be measured.
Thesis Advisor: Prof. Younjung Jo