Young-Mo Moon

The quantum under-, critical- and over-damped driven harmonic oscillators

The cases of under-, critical- and over-damping are treated for the quantum driven harmonic oscillator. Following a survey of the classical version, the quantum invariant operator for each case is constructed and their eigenvalues are evaluated. Using these eigenvalues and the Schrodinger equations, the wavefunctions are obtained for each case. From formal path integral theory, their propagators are evaluated and are checked with those obtained by the closed property formed by the complete set of wavefunctions.

Magnetization study of glassy and nanocrystalline Fe82(Zr, Hf, Nb)7B10Cu1 alloys

Abstract We report the salient features of the magnetic properties of as-quenched and annealed Fe82(Zr, Hf, Nb)7B10Cu1 alloys. Temperature dependence of magnetization was carried out and magnetic entities were investigated using the spin-wave theory and mean-field theory. Annealed alloys have been shown to exhibit good soft magnetic properties especially in high-frequency range. The presence of a rather high concentration of boron appears to have suppress the growth of BCC-Fe grains and also stabilize the amorphous matrix. Our result reveals that the reason for good soft magnetic properties is associated with the reduction of the magnetic anisotropy by rather strong exchange energy when annealing temperature is increased.

The Large Magnetocaloric Effect in Amorphous Fe80-xMnxZr10 (x = 4,6,8,10) Alloys

The Magnetization behaviour has been measured for amorphous Fe_(90-x)Mn_xZr_(10) (x = 4,6,8,10) alloys. The Curie temperature decreased from 236 K to 195 K with increasing Mn concentration (x = 4 to x = 10). The magnetization measurements were conducted at temperatures above the Curie temperature in the paramagnetic region. In all samples, the magnetic properties showed superparamagnetic behavior above Tc where the mean magnetic moment of the superparamagnetic spin clusters decreased with increasing temperature. A large magnetic entropy change, ΔS_M, which is calculated from H vs M curves associated with the ferromagnetic-paramagnetic transitions in amorphous, has been observed. With Mn concentration increasing, ΔS_M decreases 1.04, 0.95, 0.87 J/㎏ K at 222, 210, 195 K (the Curie temperature), respectively.

The Substitution Effect of Boron on Reentrant Behavior of Rapidly Solidified FeMnZr Alloys

The magnetization properties have been measured for amorphous Fe_(82)Mn_(8-x)BxZr_(10) (x = 0-8) alloys. The temperature dependence of magnetization for these alloys shows the existence of antiferromagnetic couplings between Fe atoms in low fields at low temperatures. The magnetic parameters, obtained from the magnetization behavior are consistent with the presence of mixed magnetic state. The Curie temperature and magnetic moment increased with an increase of the concentration of B and spin glass like transition observed at low temperature decreases and finally vanishes at x = 8 at%. Our result suggests that the substitution of B for Mn seems to cause an increase of magnetic order.

Soft magnetic properties in Fe-based nanocrystalline alloy

Amorphous Fe 84 Zr 7 B 6 Cu 1 Al 2 and Fe 81 B 11 Nb 7 Cu 1 alloys were annealed at 723 K and 823 K for one hour to achieve good soft magnetic properties such as large magnetoimpedance ratio (MIR) and incremental permeability ratio (PR), etc. The MIR and PR of the samples were measured from 100 kHz to 10 MHz in a cryogenic chamber with temperatures from 10 K up to 300 K. The values of coercive force reveal that the optimum temperature for better soft magnetic properties is 723 K in both samples. The maximum value of MI ratio increases drastically in the Fe 81 B 11 Nb 7 Cu 1 alloy annealed at 723 K and 823 K indicating that the sample is softened by nanocrystallization. The maximum PR values of Fe 84 Zr 7 B 6 Cu 1 Al 2 alloy measured below 1 MHz show drastic increment at above 150 K due to thermal activation of magnetic domains.

The Large Magnetocaloric Effect in Amorphous Fe 80-x Mn x Zr 10 (x = 4,6,8,10) Alloys

The Magnetization behaviour has been measured for amorphous Fe_(90-x)Mn_xZr_(10) (x = 4,6,8,10) alloys. The Curie temperature decreased from 236 K to 195 K with increasing Mn concentration (x = 4 to x = 10). The magnetization measurements were conducted at temperatures above the Curie temperature in the paramagnetic region. In all samples, the magnetic properties showed superparamagnetic behavior above Tc where the mean magnetic moment of the superparamagnetic spin clusters decreased with increasing temperature. A large magnetic entropy change, ΔS_M, which is calculated from H vs M curves associated with the ferromagnetic-paramagnetic transitions in amorphous, has been observed. With Mn concentration increasing, ΔS_M decreases 1.04, 0.95, 0.87 J/㎏ K at 222, 210, 195 K (the Curie temperature), respectively.

The Large Magnetocaloric Effect in Amorphous Fe 80-x Mn x Zr 10 (x

The Magnetization behaviour has been measured for amorphous Fe_(90-x)Mn_xZr_(10) (x = 4,6,8,10) alloys. The Curie temperature decreased from 236 K to 195 K with increasing Mn concentration (x = 4 to x = 10). The magnetization measurements were conducted at temperatures above the Curie temperature in the paramagnetic region. In all samples, the magnetic properties showed superparamagnetic behavior above Tc where the mean magnetic moment of the superparamagnetic spin clusters decreased with increasing temperature. A large magnetic entropy change, ΔS_M, which is calculated from H vs M curves associated with the ferromagnetic-paramagnetic transitions in amorphous, has been observed. With Mn concentration increasing, ΔS_M decreases 1.04, 0.95, 0.87 J/㎏ K at 222, 210, 195 K (the Curie temperature), respectively.