Magnetic dot arrays with perpendicular magnetic anisotropy were fabricated by patterning Co(80)Pt(20)-alloy continuous films by means of laser interference lithography. As commonly seen in large dot arrays, there is a large difference in the switching field between dots. Here we investigate the origin of this large switching field distribution, by using the anomalous Hall effect (AHE). The high sensitivity of the AHE permits us to measure the magnetic reversal of individual dots in an array of 80 dots with a diameter of 180 nm. By taking 1000 hysteresis loops we reveal the thermally induced switching field distribution SFD(T) of individual dots inside the array. The SFD(T) of the first and last switching dots were fitted to an Arrhenius model, and a clear difference in switching volume and magnetic anisotropy was observed between dots switching at low and high fields.

Tunneling anisotropic magnetoresistance (TAMR) has been characterized in junctions comprised of facecentered cubic (fcc) Co ( 111) ferromagnetic electrodes grown epitaxially on sapphire substrates, amorphous AlO x tunnel barriers, and nonmagnetic Al counterelectrodes. Large TAMR ratios have been found, up to ∼7.5% and ∼11% (at 5 K), for the in-plane and out-of-plane magnetization geometry, respectively. Such large TAMR values were not expected a priori, given the weak anisotropy of the (bulk) Co bands due to spin-orbit interaction, and the absence of Co (111) surface states that cross the Fermi energy. Both the in-plane and out-of-plane TAMR effects exhibit a predominantly twofold symmetry, and a strong bias dependence. The in-plane TAMR shows a maximum along the (twofold) magnetic hard axis, suggesting a relation between magnetic anisotropy and TAMR. We propose that uniaxial strain in combination with Bychkov-Rashba spin-orbit interaction, producing an interfacial tunneling DOS that depends on the magnetization direction, is responsible for the TAMR effect. The importance of the interfacial Co/AlO x (electronic) structure for the TAMR effect is underlined by measurements on junctions with overoxidized AlO x barriers, which show markedly different bias and angle dependence.

C 60 fullerenes are interesting molecular semiconductors for spintronics since they exhibit weak spin-orbit and hyperfine interactions, which is a prerequisite for long spin lifetimes. We report spin-polarized transport in spin-valve-like structures containing ultrathin (<10 nm) C 60 layers, ferromagnetic (FM) epitaxial face-centeredcubic (fcc) Co (111) contacts, AlO x tunnel barriers, and nonmagnetic Al counter electrodes. Even though genuine spin-valve behavior cannot occur for only one FM contact, we find significant tunneling anisotropic magnetoresistance (TAMR) upon rotating the in-plane magnetization, originating from spin-orbit interaction (SOI) induced anisotropy of the fcc (111) Co bands. The uniaxial magnetocrystalline anisotropy of the Co electrodes results in a predominantly twofold symmetric in-plane TAMR effect. We investigated the TAMR effect in the direct tunneling regime (2 nm C 60 ), at the transition point to two-step tunneling (4 nm C 60 ), and in the multistep regime (8 nm C 60 ). A sizable TAMR of 4.5% is found at 5 K under application of a 500-mT in-plane magnetic field for C 60 layers of 2 nm, which is strongly suppressed at 8 nm thickness, indicating that TAMR may strongly contribute to the "spin-valve" signal for direct tunneling, but not for multistep tunneling. The TAMR effect is proposed to be due to a combination of SOI induced modulation of the tunneling DOS upon rotating the in-plane magnetization of the fcc epitaxial Co thin film, resonant tunneling processes involving interfacial states, and different Bychkov-Rashba SOI at the different interfaces.

The authors propose a concept in mass data storage system architecture, in which thousands of read/write heads, storage robots or StoBots move independently over a large, flat storage medium. This concept, which has not been previously proposed, offers new degrees of freedom in data storage systems design, which could lead to a superior performance over conventional systems such as hard disks and tape. The impact of different file system architectures on the access time and data-rate of the StoBot drive is investigated.

The interaction between ferromagnetic surfaces and organic semiconductors leads to the formation of hybrid interfacial states. As a consequence, the local magnetic moment is altered, a hybrid interfacial density of states (DOS) is formed, and spin-dependent shifts of energy levels occur. Here, we show that this hybridization affects spin transport across the interface significantly. We report spin-dependent electronic transport measurements for tunnel junctions comprising C molecular thin films grown on top of face-centered-cubic (fcc) epitaxial Co electrodes, an AlO tunnel barrier, and an Al counter electrode. Since only one ferromagnetic electrode (Co) is present, spin-polarized transport is due to tunneling anisotropic magnetoresistance (TAMR). An in-plane TAMR ratio of approximately 0.7% has been measured at 5 K under application of a magnetic field of 800 mT. The magnetic switching behavior shows some remarkable features, which are attributed to the rotation of interfacial magnetic moments. This behavior can be ascribed to the magnetic coupling between the Co thin films and the newly formed Co/C hybridized interfacial states. Using the Tedrow-Meservey technique, the tunnel spin polarization of the Co/C interface was found to be 43%.