Crossover from Kondo-Assisted Suppression to Co-Tunneling Enhancement of Tunneling Magnetoresistance via Ferromagnetic Nanodots in MgO Tunnel Barriers
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- 作者：Hyunsoo Yang ; See-Hun Yang ; Stuart S. P. Parkin
- 刊名：Nano Letters
- 出版年：2008
- 出版时间：January 2008
- 年：2008
- 卷：8
- 期：1
- 页码：340 - 344
- 全文大小：242K
- 年卷期：v.8,no.1(January 2008)
- ISSN：1530-6992
文摘
The dependence of the tunneling magnetoresistance (TMR) of planar magnetic tunnel junctions on the size of magnetic nanodots incorporatedwithin MgO tunnel barriers is explored. At low temperatures, in the Coulomb blockade (CB) regime, for smaller nanodots the conductance ofthe junction is increased at low bias consistent with Kondo-assisted tunneling and the TMR is suppressed. For slightly larger nanodots butwithin the CB regime, the TMR is enhanced at low bias, consistent with co-tunneling. Magnetic tunnel junctions (MTJ) exhibit giantmagnetoresistance in small magnetic fields that arises from the flow of spin-polarized current through an ultrathin tunnel barrier separatingtwo magnetic electrodes. The current through an MTJ device depends on the magnetic orientation of the electrodes and is typically higherwhen the electrode moments are parallel than when they are antiparallel.1 It has recently been demonstrated that the spin polarization of thetunneling current can be greatly enhanced by using crystalline tunnel barriers formed from MgO as compared with conventional amorphousbarriers formed from alumina, due to spin filtering across the MgO layer.2-6 The magneto-transport properties of magnetic granular alloys andmagnetic tunnel junction devices with magnetic nanodots embedded in amorphous dielectric matrices7,8 and tunnel barriers,9,10 respectively,have been studied by several groups, but no systematic studies of the dependence on these properties on the nanodot size have been made.