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Magneto-transport properties of magnetic tunnelling transistors at low and room temperatures
Quang, H D,Huu, C X,Oh, S K,Dang, V S,Sinh, N H,Yu, S C IOP Pub 2006 Nanotechnology Vol.17 No.14
<P>Si(100)/CoFe/AlO<SUB><I>x</I></SUB><I>/</I>CoFe/FeMn/Cu/Ta magnetic tunnelling transistors (MTTs) with differing base thicknesses (<I>W</I>) were investigated. The magneto-transport properties of the MTTs were measured at 77?K and room temperature (RT). We obtained magneto-current ratios of 48.3% and 55.9% for emitter–base bias voltages of 1.45 and 2.0?V, respectively, at 77?K. The transfer ratios are 2.83 ? 10<SUP>−5</SUP> and 1.52 ? 10<SUP>−4</SUP>, respectively, corresponding to bias voltages of 1.45 and 2.0?V. Moreover, the highest tunnel magneto-resistance (TMR) ratios turned out to be 12% and 20% for a base thickness of 30?Šat RT and 77?K, respectively. These properties raise not only some fundamental questions regarding the phenomenon of spin-independent tunnelling at low and room temperatures, but also show some promising aspect for magneto-electronic applications. In addition, we attempted to elucidate the reason behind the outstanding TMR effect at low and room temperatures. Finally, the origin of the decrease in the mean free path asymmetry (<img SRC='http://ej.iop.org/images/0957-4484/17/14/004/nano218705ieqn1.gif' ALIGN='MIDDLE' ALT='\lambda^{ \uparrow }/\lambda^{\downarrow } '/>) was clarified by using x-ray photoelectron spectroscopy profile analysis of the elements existing in the interface between Si and the CoFe base (Co, Fe, Al, Si, O). </P>
Critical behavior and magnetic entropy change in La_0.7Ca_0.3Mn_0.9Zn_0.1O_3 perovskite manganite
판더롱,P.Q. Thanh,N.H. Sinh,K.W. Lee,유성초 한국물리학회 2011 Current Applied Physics Vol.11 No.3
We studied the critical behavior and magnetic entropy change in a perovskite-manganite compound of La_0.7Ca_0.3Mn_0.9Zn_0.1O_3 around its Curie temperature of T_C = 206.75 K. Experimental results revealed that the sample exhibited the second-order magnetic phase transition with the exponents β = 0.474 and γ = 1.152 close to those expected from the mean-field theory (β = 0.5 and γ = 1.0). In the vicinity of T_C,the magnetic entropy change DSM reached maximum values of 1.1, 1.7, and 2.7 J/kg K under magnetic-field variations of 10, 20, and 35 kOe, respectively. These ΔS_M values are much lower than those reported previously on the parent compound of La_0.7Ca_0.3MnO_3. The nature of this phenomenon is discussed by means of the characteristics of the magnetic phase transition, and critical exponents.