Sung Jong Lee

Ferroelectric and magnetic properties of CdMnS films prepared by coevaporation

We report on impurity ferroelectricity and ferromagnetic properties in semiconductor-structured CdMnS films. We observed ferroelectric hysteresis in CdMnS. A remnant polarization of 1.72 μC/cm2 and a coercive field of 14.3 kV/cm were obtained in samples with Mn concentration below 2%. The coevaporated CdMnS samples become ferromagnetic when doped with Au, with a spontaneous magnetization of 1.39×10−6 emu and a coercive magnetic field of 75.4 gauss at 10 K, and the Curie point was found to be higher than room temperature. Through magnetic force microscopy, we observed clear magnetic clusters with sizes ranging from a few nanometers to 102 nm, and found the magnetization to be highly dependent on Au concentration. A combination of this ferroelectricity in CdMnS and ferromagnetism in Au-doped CdMnS may find use in ternary bit nonvolatile memory devices.

Spin currents modulated by magnetic barriers in semiconductor nanowires

We present the properties of ballistic spin transport through magnetic barrier structures in semiconductor nanowires. Landauers approach is adopted for the calculation of spin transport properties for various host material nanowires which are remarkably different from each other in the effective g-factor, g*. The spin polarization effect on the conductance of a nanowire is more efficient than that of a purely two-dimensional electron gas. Especially, when the bias increases the conductance of a nanowire with small g* is quantized as a step function and its spin dependence disappears. However, these behaviours are broken for a host material with large g* and the spin-dependent splitting appears in this case. We achieve the enhancement of the spin polarization effect on currents by increasing the number of magnetic barriers and we can finally obtain the perfect spin-polarized effect on the conductance.

Modulation of the Curie temperature in ferromagnetic/ferroelectric hybrid double quantum wells

We propose a ferromagnetic/ferroelectric hybrid double quantum well structure, and present an investigation of the Curie temperature (Tc) modulation in this quantum structure. The combined effects of applied electric fields and spontaneous electric polarization are considered for a system that consists of a Mn \delta-doped well, a barrier, and a p-type ferroelectric well. We calculate the change in the envelope functions of carriers at the lowest energy sub-band, resulting from applied electric fields and switching the dipole polarization. By reversing the depolarizing field, we can achieve two different ferromagnetic transition temperatures of the ferromagnetic quantum well in a fixed applied electric field. The Curie temperature strongly depends on the position of the Mn \delta-doped layer and the polarization strength of the ferroelectric well.

Ferroelectric Properties of Mn‐implanted CdTe

We report a study of ferroelectricity in CdTe:Mn, which were prepared by implantation of CdTe wafers with 200‐keV Mn ions to a dose of 5×1016 cm−2 and subsequently treated by rapid thermal annealing. An insulating layer was created by the implantation in the surface region of the samples. Ferroelectric characterization of the implanted sample revealed a clear hysteresis in its polarization‐voltage curves. The remnant polarization of CdTe:Mn amounts to 0.64 μC/cm2 at 400 Hz. The polarization decreases with increasing temperature in a continuous and diffusive manner. Capacitance measurement demonstrated a maximum capacitance at 140°C, and fitting of the data with Curie‐Weiss law shows the occurrence of a second‐order type phase transition.

Comparison of ferromagnetic properties between InMnP and GaMnN quantum wells

We present the ferromagnetic phase diagram of In1−xMnxP and Ga1−xMnxN quantum wells using the envelope‐function approach of the effective mass approximation with a multi‐subband model. The dependence of the Curie temperature (Tc) on the hole density exhibits different behavior in each case. In a multi‐subband model, the Curie temperature of the In1−xMnxP quantum well is obtained about 68 K, and the Curie temperature of the p‐type Ga1−xMnxN quantum well can be above room temperature, unless the spin‐exchange interaction integral is abnormally small.

Wire Fixation Technique for the Tibial Tubercle Osteotomy in Total Knee Arthroplasty

Purpose: The purpose of this study is to evaluate the clinical results of wire fixation technique for tibial tubercle osteotomy in total knee arthroplasty. Materials and Methods: Twenty-three cases who underwent TKA with tibial tubercle osteotomy and wire fixation technique for the extensile exposure between January, 1982 and April, 2001, were reviewed. Seventeen cases were male and six cases female. The average period of follow-up was 58 months. The average age was 62.3 years (minimal: 38, maximal: 74). Five cases underwent tibial tubercle osteotomy for primary TKA and the preoperative diagnoses were degenerative osteoarthritis in 2 cases, posttraumatic osteoarthritis in 1 case and rheumatoid arthritis in 2 cases. Eighteen cases underwent tibial tubercle osteotomy for revision TKA due to the infected TKA in 10 cases and aseptic loosening in 8 cases. Osteotomized tibial tubercle in size of cm was achieved by using oscillating saw and curved osteotome from the point of 2 cm distal to the articular surface of proximal tibia to 8 cm below the tibial tubercle. Six holes were drilled with 1 cm distance for 3 wires passage. The tubercle fragment was fixed with 3 wires and the wires were bent around the tibial stem in the medullary canal for passage through tubercle fragment. The passive range of motion was started within one week after the operation. We evaluated the preoperative and postoperative range of motion and the radiologic bony union was assessed by lateral radiograph. The clinical results were assessed by Knee Society Knee Score. Results: The bony union was achieved in twenty-two cases about 13 moths after the operation, and fixation loss was observed in one case. The average range of motion were postoperatively. The average clinical knee scores of pain and function were 51 (40-57) point, 58 (45-70) point preoperatively and 54 (50-65) point, 65 (54-78) point postoperatively. Two complications were noted with one case of infection and fixation loss due to injury in each. Conclusion: Wire fixation for tibial tubercle osteotomy in total knee arthroplasty results in firm fixation of tubercle fragment, therefore it seems to be an useful technique in exposure for total knee arthroplasty.