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Magnetic and Transport Properties of Amorphous Ge-Mn Thin Films
송상훈,임상호,J Moodera,정명화,T Santos 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.49 No.III
The magnetic and transport properties are investigated in well-characterized Ge1.xMnx (x in at.%) amorphous semiconductor thin films for a large range of Mn compositions, prepared by using thermal co-evaporation onto oxidized Si or glass substrates held either at room temperature or quench condensed onto LN2-cooled surface. Magnetic hysteresis measurements at room temperature show saturation occurring by 1 2 kOe for all samples. The temperature dependence of the magnetization between 4 K and 300 K, measured at an applied field of 15 kOe and for zerofield cooled condition, exhibit a concave shape, different from the usual Brillouin behavior. The saturation magnetization at room temperature is found to range from 0.5 to 7 emu/cc. The highest magnetic moment observed per Mn ion is 0.76 Bohr magneton (μB) at 4 K at an intermediate composition x = 38.5 %. At x = 16.7 % where detailed transport measurements are carried out, the anomalous Hall effect is observed at 300 K, and the temperature dependence of the Hall effect is rather complicated. The magnetoresistance, being 1 % at an applied field of 50 kOe, changes sign at around 200 K.
Magnetic Tunnel Junctions with Magnesium Oxide Barriers
Taro Nagahama,Jagadeesh S. Moodera 한국자기학회 2006 Journal of Magnetics Vol.11 No.4
Spin dependent tunneling has enormously activated the field of magnetism in general, and in particular spin transport studies, in the past ten years. Thousands of articles related to the subject have appeared with many fundamental results. Importantly, there is great interest in their potential for application. There was another surge of activity in this field since the past five years - created by the theoretical prediction of a large tunnel magnetoresistance that arises due to band symmetry matched coherent tunneling in epitaxial magnetic tunnel junctions with (001) MgO barrier and experimentally well demonstrated. This further development in the field has boosted the excitement in both fundamental science as well as the possibility of application in such as magnetic random access memory, ultra sensitive read heads, biosensors and spin torque diodes. This review is a brief coverage of the field highlighting the literature that deals with magnetic tunnel junctions having epitaxial MgO tunnel barriers
Large Spin Diffusion Length in an Amorphous Organic Semiconductor
Shim, J. H.,Raman, K. V.,Park, Y. J.,Santos, T. S.,Miao, G. X.,Satpati, B.,Moodera, J. S. American Physical Society 2008 Physical Review Letters Vol.100 No.22
<P>We directly measured a spin diffusion length (lambdas) of 13.3 nm in amorphous organic semiconductor (OS) rubrene (C42H28) by spin polarized tunneling. In comparison, no spin-conserved transport has been reported in amorphous Si or Ge. Absence of dangling bond defects can explain the spin transport behavior in amorphous OS. Furthermore, when rubrene barriers were grown on a seed layer, the elastic tunneling characteristics were greatly enhanced. Based on our findings, lambdas in single-crystalline rubrene can be expected to reach even millimeters, showing the potential for organic spintronics development.</P>
Logarithmic singularities and quantum oscillations in magnetically doped topological insulators
Nandi, D.,Sodemann, Inti,Shain, K.,Lee, G. H.,Huang, K.-F.,Chang, Cui-Zu,Ou, Yunbo,Lee, S. P.,Ward, J.,Moodera, J. S.,Kim, P.,Yacoby, A. American Physical Society 2018 Physical Review B Vol.97 No.8
<P>We report magnetotransport measurements on magnetically doped (Bi, Sb)(2)Te-3 films grown by molecular beam epitaxy. In Hall bar devices, we observe logarithmic dependence of transport coefficients in temperature and bias voltage which can be understood to arise from electron-electron interaction corrections to the conductivity and self-heating. Submicron scale devices exhibit intriguing quantum oscillations at high magnetic fields with dependence on bias voltage. The observed quantum oscillations can be attributed to bulk and surface transport.</P>