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묽은 강자성 반도체 CdMnTM(Fe,Co,Cr)Te 결정의 성장과 자기-광학적 특성에 관한 연구
Reports NRF is supported by Research Projects( 묽은 강자성 반도체 CdMnTM(Fe,Co,Cr)Te 결정의 성장과 자기-광학적 특성에 관한 연구 | 2004 Year 신청요강 다운로드 PDF다운로드 | 황영훈(울산대학교) ) data is submitted to the NRF Project Results
Researcher who has been awarded a research grant by Humanities and Social Studies Support Program of NRF has to submit an end product within 6 months(* depend on the form of business)
사업별 신청요강보기
  • Researchers have entered the information directly to the NRF of Korea research support system
Project Number C00008
Year(selected) 2004 Year
the present condition of Project 종료
State of proposition 재단승인
Completion Date 2007년 10월 23일
Year type 결과보고
Year(final report) 2007년
Research Summary
  • Korean
  • 수직 Bridgman법으로 묽은 자성반도체 Cd1-x-yMnxTMyTe (TM = Fe, Co, Cr)를 성장시켜 광학적, 자기적, 자기광학적 특성을 연구하였다. XRD 측정으로부터 성장시킨 단결정의 결정구조는 섬아연광 구조였고, EPMA와 XRD에 의하여 전이금속 TM의 성분비를 결정하였다. TM 성분비 y증가에 대하여 격자상수는 감소함을 보였다, 온도와 성분비에 따른 Cd1-x-yMnxTMyTe 단결정의 광흡수를 측정하였다. 모체 물질 CdTe에 다른 원자 크기를 가지는 TM 이온을 치환시킴으로써, 에너지 띠 간격은 Vegrad’s 법칙 따라서 TM 조성비에 선형적으로 의존하였다. 상온에서 1.3 ~ 6.0 eV의 에너지 범위에서 분광 타원해석기를 사용하여 Cd1-x-yMnxTMyTe의 복소 유전함수를 측정하였다. SCP (standard critical point) 모델을 사용하여 이들 결과를 분석하였고, TM 3d 준위와 Cd1-xMnxTe의 가전자 띠와 전도띠 사이의 혼성 효과 때문에 TM 성분비 y 증가에 따른 임계 에너지 E1, E1+d1, and E2 는 변화하였다. 12~300 K의 온도 영역에서 TM 성분비에 따른 PL을 측정하였다. 기본적인 띠 간격을 통한 엑시톤 재결합의 특이한 방출 피크를 관측하였다. 구속 엑시톤 피크의 온도 의존성으로부터 Mn 조성비 x와 TM 조성비 y 증가에 대하여 Varshni 온도 변수 a는 증가하였고, b는 감소하는 경향을 보였다. Cd1-x-yMnxCoyTe의 자기적, 수송 특성으로부터 300 K까지 강자성 정렬을 보였고, Co를 첨가함에 따라서, 모든 시료는 n-형 전기 전도도를 보였다. Cd1-x-yMnxFe0.38Te의 Fe mole당 자화율은 같은 조성의 CdMnTe과 비교하여 Fe를 증가함에 따라서 증가함을 보였다. Cd0.562Mn0.38Fe0.058Te 결정의 경우 온도에 따른 자화율은 특이한 거동을 보였다. Cd1-x-yMnxCryTe는 350 K 이상에서 강자성을 보였고, 의 자기적, 수송 특성으로부터 300 K까지 강자성 정렬을 보였고, Cr을 첨가함에 따라서, 보자력 장과 자기 모멘트 값은 증가하였다. Cd1-x-yMnxTMyTe의 패러데이 회전을 조사하였고, 10~300 K의 온도 영역에서 Verdet 상수를 측정하였다. Cd1-x-yMnxTMyTe의 패러데이 회전은 CdMnTe과 비교하여 증가함을 보였고, 자화율과 sp-d 교환 상호작용의 항으로 설명하였다.
  • English
  • We have studied the optical, magnetic, and magneto-optical properties of diluted magnetic semiconductor Cd1-x-yMnxTMyTe (TM = Fe, Co, Cr) crystals grown by vertical Bridgman method. The crystal structure of the grown crystals was zinc-blende, which was examined by XRD measurements and the mole fraction of a transition metal was determined by EPMA and XRD. The lattice constant decreases linearly with increasing TM contents y. The bandgap energy was depended on y linearly and blue-shifted with decreasing T. The increase of the energy gap with y may be due to a decrease in the lattice constant. Varshni temperature parameter α increased linearly with increasing TM concentration y, while β decreased. The photoluminescence on the Cd1-x-yMnxTMyTe for a series of TM compositions was measured over the temperature range of 12~300 K. We identified three specific emission peaks associated with the excitonic recombination across the fundamental gap. From the temperature dependence of the bound exciton peak, the Varshni temperature parameter was found to increase linearly with increasing Mn concentration x and TM concentration y, while β decreased with x and y. The complex dielectric functions of Cd1-x-yMnxTMyTe were measured using spectroscopic ellipsometry in the range of 1.3~ 6.0 eV photon energy at room temperature. From the fitting with the SCP model, we obtained the energies E0, E1, E1+d1, and E2 with various TM concentration y and calculated the spin-orbit splitting energies. The E1, E1+d1, and E2 energies were decreased with increasing TM composition, which is due to the hybridization effect of the valence and conduction bands in Cd1-xMnxTe with TM 3d levels. The magnetic and transport properties of Cd1-x-yMnxTMyTe single crystals were investigated. For Cd1-xMnxTe compounds, for x<0.2 are paramagnetics; for 0.2<x<0.60 spin-glass phase; and for 0.60<x<0.82 antiferromagnetically ordered by low-field magnetic susceptibility measurements. The Cd0.63-yMn0.37CoyTe crystals showed the ferromagnetic ordering up to 300 K and n type conductivity by the addition of Co. The coercive field was 118 and 83 Oe at 300 K for Cd0.63-yMn0.37CoyTe with y = 0.02 and 0.04, respectively, and the coercive field decreased with increasing Co concentration y. The magnetic susceptibility per Fe mole of Cd1x-yMn0.38FeyTe increases with increasing Fe concentration, which is same as that of CdMnTe. The Cd0.562Mn0.38Fe0.058Te crystal showed the peculiar magnetic behavior, i.e. the temperature dependent magnetic susceptibility in 100 Oe above Tc (=20.1 K). The Cd0.64-yMn0.36CryTe crystals showed ferromagnetic up to 350 K. The coercive field was 42 Oe at 300 K for Cd0.55Mn0.36Cr0.09Te crystal and the coercive field increased with Cr-addition. Although the measured magnetic moment per Cr atom for Cd0.64-yMn0.36CryTe low y at 1 T was very low, the magnetic moment was rapidly increased with increased Cr-addition.
    To investigate the Faraday rotation for Cd1-x-yMnxTMyTe, the Verdet constants were measured at 10 K~300 K and the Faraday rotation of Cd1-x-yMnxTMyTe was found to be much larger than that of CdMnTe crystals. The enhancement of the quaternary samples compared with ternary Cd1-xMnxTe compounds in the Faraday rotation was able to be summarized in terms of the sp-d exchange content and the magnetic susceptibility.
Research result report
  • Abstract
  • We have studied the optical, magnetic, and magneto-optical properties of diluted magnetic semiconductor Cd1-x-yMnxTMyTe (TM = Fe, Co, Cr) crystals grown by vertical Bridgman method. The crystal structure of the grown crystals was zinc-blende, which was examined by XRD measurements and the mole fraction of a transition metal was determined by EPMA and XRD. The lattice constant decreases linearly with increasing TM contents y. The decrease in the lattice constant is due to the smaller Mn (a = 1.326 Å), Fe (a = 1.170 Å), Co (a = 1.225 Å), and Cr (a = 1.2807 Å) covalent radii compared with Cd (a = 1.405 Å). The equations of the lattice constants for samples added different TM atoms to ternary Cd1-xMnxTe compound were a = 6.485-0.146x-0.139y (Fe), a = 6.485-0.146x-0.236y (Co), and a = 6.485-0.146x-0.231y (Cr), respectively, which obeyed Vegard’s law well.
    The bandgap energy was depended on y linearly and blue-shifted with decreasing T. The increase of the energy gap with y may be due to a decrease in the lattice constant.
    The photoluminescence on the Cd1-x-yMnxTMyTe for a series of TM compositions was measured over the temperature range of 12~300 K. From the temperature dependence of the bound exciton peak, the Varshni temperature parameter was found to increase linearly with increasing Mn concentration x and TM concentration y, while β decreased with x and y.
    We compared the FWHM of the measured PL emission spectra for our samples with the calculated FWHM due to alloy broadening. The complex dielectric functions of Cd1-x-yMnxTMyTe were measured using spectroscopic ellipsometry in the range of 1.3 ~ 6.0 eV photon energy at room temperature. From the fitting with the SCP model, we obtained the energies E0, E1, E1+d1, and E2 with various TM concentration y and calculated the spin-orbit splitting energies. The E1, E1+d1, and E2 energies were decreased with increasing TM composition, which is due to the hybridization effect of the valence and conduction bands in Cd1-xMnxTe with TM 3d levels.
    The magnetic and transport properties of Cd1-x-yMnxTMyTe single crystals were investigated.
    For Cd1-xMnxTe compounds, for x<0.2 are paramagnetics; for 0.2<x<0.60 spin-glass phase; and for 0.60<x<0.82 antiferromagnetically ordered by low-field magnetic susceptibility measurements.
    The Cd0.63-yMn0.37CoyTe crystals showed the ferromagnetic ordering up to 300 K and n type conductivity by the addition of Co. The magnetic susceptibility per Fe mole of Cd1x-yMn0.38FeyTe increases with increasing Fe concentration, which is same as that of CdMnTe.
    The Cd0.562Mn0.38Fe0.058Te crystal showed the peculiar magnetic behavior, i.e. the temperature dependent magnetic susceptibility in 100 Oe above Tc (=20.1 K). The Cd0.64-yMn0.36CryTe crystals showed ferromagnetic up to 350 K. The coercive field was 42 Oe at 300 K for Cd0.55Mn0.36Cr0.09Te crystal and the coercive field increased with Cr-addition. Although the measured magnetic moment per Cr atom for Cd0.64-yMn0.36CryTe low y at 1 T was very low, the magnetic moment was rapidly increased with increased Cr-addition. To investigate the Faraday rotation for Cd1-x-yMnxTMyTe, the Verdet constants were measured at 10 K-300 K and the Faraday rotation of Cd1-x-yMnxTMyTe was found to be much larger than that of CdMnTe crystals. The enhancement of the quaternary samples compared with ternary Cd1-xMnxTe compounds in the Faraday rotation was able to be summarized in terms of the sp-d exchange content and the magnetic susceptibility.
  • Research result and Utilization method
  • Faraday 회전은 자기광학 소자로 활용하기 위한 중요한 기초 자료로서 광 아이솔레이터 소자로 활용하기 위한 실험이다. 본 연구에서 개발한 자기광학 소자인 CdMnTe와 CdMnTMTe의 경우 기존에 알려진 자기광학 소자보다 회전비가 커다는 것을 확인하였고 광 아이솔레이션 비율도 높게 나타났다. 광통신 소자 중 하나인 광 아이솔레이터는 현재까지 국내에서 개발된 경우가 없으며, 해외에서 전량 수입되고 있는 실정이다. 따라서 본 연구에서 개발한 광 아이솔레이터를 이용하면 산업적인 측면뿐만 아니라 원천기술의 확보차원에서 중요한 역할을 할 수 있을 것으로 기대된다.
  • Index terms
  • diluted magnetic semiconductor, vertical Bridgman method, Cd1-x-yMnxTMyTe, X-ray diffraction, zincblend, lattice constants, EPMA, photoluminescence, bound exciton, Varshni temperature parameter, FWHM, broadening, spectroscopic ellipsometry, SCP model, spin-orbit splitting energies, hybridization effect, paramagnetics, spin-glass phase, antiferromagnetic, ferromagnetic, magnetic susceptibility, Faraday rotation, Verdet constants, sp-d exchange,
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