Spin-polarized transport in ferromagnetic tunnel junctions, characterized by tunnel magnetoresistance, has already been proven to have great potential for application in the field of spintronics and in magnetic random access memories. Until recently, in such a junction the insulating barrier played only a passive role, namely to facilitate electron tunnelling between the ferromagnetic electrodes. However, new possibilities emerged when ferroelectric materials were used for the insulating barrier, as these possess a permanent dielectric polarization switchable between two stable states. Adding to the two different magnetization alignments of the electrode, four non-volatile states are therefore possible in such multiferroic tunnel junctions. Here, we show that owing to the coupling between magnetization and ferroelectric polarization at the interface between the electrode and barrier of a multiferroic tunnel junction, the spin polarization of the tunnelling electrons can be reversibly and remanently inverted by switching the ferroelectric polarization of the barrier. Selecting the spin direction of the tunnelling electrons by short electric pulses in the nanosecond range rather than by an applied magnetic field enables new possibilities for spin control in spintronic devices.

Spontaneous polarization of ferroelectric materials has been for a long time proposed as binary information support, but it suffers so far from destructive readout. A nondestructive resistive readout of the ferroelectric polarization state in a metal-ferroelectric-metal capacitor would thus be advantageous for data storage applications. Combing conducting force microscopy and piezoelectric force microscopy, we unambiguously show that ferroelectric polarization direction and resistance state are correlated for epitaxial ferroelectric Pb(Zr(0.2)Ti(0.8))O(3) nanoscale capacitors prepared by self-assembly methods. For intermediate ferroelectric layer thickness (∼9 nm) sandwiched between copper and La(0.7)Sr(0.3)MnO(3) electrodes we achieved giant electroresistance with a resistance ratio of >1500 and high switching current densities (>10 A/cm(2)) necessary for effective resistive readout. The present approach uses metal-ferroelectric-metal devices at room temperature and, therefore, significantly advances the use of ferroelectric-based resistive switching.

Fully epitaxial BaTiO(3)/CoFe(2)O(4) ferroelectric/ferromagnetic multilayered nanodot arrays, a new type of magnetoelectric (ME) nanocomposite with both horizontal and vertical orderings, were fabricated via a stencil-derived direct epitaxy technique. By reducing the clamping effect, ferroelectric domain modification and distinct magnetization change proportional to different interfacial area around the BaTiO(3) phase transition temperatures were found, which may pave the way to quantitative introducing of ME coupling at nanoscale and build high density multistate memory devices.

In ferroelectric tunnel junctions, the ferroelectric polarization state of the barrier influences the quantum-mechanical tunneling through the junction, resulting in tunnel electroresistance (TER). Here, we investigate tunnel electroresistance in Co/PbZr0.2Ti0.8O3/La0.7Sr0.3MnO3 tunnel junctions. The ferroelectric polarization in tunnel junctions with 1.2-1.6 nm (three to four unit cells) PbZr0.2Ti0.8O3 thickness and an area of 0.04 μm2 can be switched by about 1 V yielding a resistive ON/OFF-ratio of about 300 at 0.4 V. Combined piezoresponse force microscopy and electronic transport investigations of these junctions reveal that the transport mechanism is quantum tunneling and the resistive switching in these junctions is due only to ferroelectric switching.

The influence of the high-temperature annealing ambient, i.e., N 2 and Ar on size controlled Si nanocrystals ͑NCs͒ ranging from ϳ2 to ϳ6 nm embedded in SiO 2 has been investigated in detail. Generally, N 2 annealing is proven to be beneficial as the dangling bond density ͑P b defects at the NC/ SiO 2 interface͒ is about half, accompanied by a doubled photoluminescence ͑PL͒ intensity. The PL blueshift of N 2 annealed samples compared to Ar-annealed samples ͑N-blueshift͒ was found to be pronounced only for small NCs whereas it appears to be insignificant for larger NCs. The origin of this N-blueshift was previously attributed to a growth suppression of the NCs by the presence of N during the annealing process. However, no evidence for this assumption is found by time-resolved PL, as the luminescence decay times are similar despite considerable N-blueshift. The exact location of the N incorporated during annealing was investigated by time-of-flight-SIMS and electron-spin resonance. Besides the distinct N enrichment in the NC layer, the K 0 center ͑ • Si ϵ N 3 ͒ was detected indicating the formation of an interfacial N layer at the NC/ SiO 2 interface. Elastic recoil detection analysis enabled the quantification of the incorporated N as well as the excess Si. Combined with transmission electron microscopy analysis ͑determination of NC size͒ the calculation of the NC density per superlattice layer and the thickness of the interfacial N layer were achieved. It turns out that ϳ5 ϫ 10 14 N atoms cm −2 exist at the NC surface, which is well in accordance to the optimum value of the bulk Si/ SiO 2 interface. These results strongly support our recently suggested explanation for the N-blueshift that is based on an increased NC band gap by the influence of interfacial N on the polarity of the surface terminating groups.