Equipe 101 : Nanomagnétisme et électronique de spinInternational audienceSingle-crystalline V/Fe(0.7 nm)/MgO(1.2nm)/Fe(20 nm) magnetic tunnel junctions are studied to quantify the influence of an electric field on the Fe/MgO interface magnetic anisotropy. The thinnest Fe soft layer has a perpendicular magnetic anisotropy (PMA), whereas the thickest Fe layer acts as sensor for magnetic anisotropy changes. When electrons are added at the PMA Fe/MgO interface (negative voltage), no anisotropy changes are observed. For positive voltage, the anisotropy constant decreases with increasing bias voltage. A huge 1150 fJV(-1) m(-1) anisotropy variation with field is observed and the magnetization is found to turn from out-of-plane to in-plane of the sample with the applied voltage

International audienceElectron-beam ͑E-beam͒ directed assembly, which combines the long-range phase and placement registration of e-beam lithography with the sharp dot size and spacing uniformity of block copolymer self assembly, is considered highly promising for fabricating templates that meet the tight magnetic specifications required for write synchronization in bit patterned media magnetic recording systems. In our study, we show that this approach also yields a narrower magnetic switching field distribution ͑SFD͒ than e-beam patterning or block copolymer self-assembly alone. We demonstrate that the pattern uniformity, i.e., island diameter and placement distributions are also important for achieving tight magnetic SFDs. Bit patterned media ͑BPM͒ magnetic recording systems at densities in excess of 1 Tb/ in 2 require an extremely tight lithographic bit placement accuracy and a narrow size distribution of less than 5% in order to achieve good write synchronization between the recording head and the patterned media. 1 Nanoimprint technology with master molds fabricated via e-beam directed assembly of block copolymer films is considered a very promising cost-effective approach for creating highly uniform magnetic dot patterns over large areas. 2,3 In addition to the tight lithographic specifications for BPM, a narrow switching field distribution ͑SFD͒ of the magnetic dots is critical to ensure exact bit addressability without overwriting adjacent bits

In combining spin- and symmetry-resolved photoemission, magnetotransport measurements and ab initio calculations we detangled the electronic states involved in the electronic transport in Fe(1-x)Co(x)(001)/MgO/Fe(1-x)Co(x)(001) magnetic tunnel junctions. Contrary to previous theoretical predictions, we observe a large reduction in TMR (from 530 to 200% at 20 K) for Co content above 25 atomic% as well as anomalies in the conductance curves. We demonstrate that these unexpected behaviors originate from a minority spin state with Δ(1) symmetry that exists below the Fermi level for high Co concentration. Using angle-resolved photoemission, this state is shown to be a two-dimensional state that occurs at both Fe(1-x)Co(x)(001) free surface, and more importantly at the interface with MgO. The combination of this interface state with the peculiar density of empty states due to chemical disorder allows us to describe in details the complex conduction behavior in this system.