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Abstract: A method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. In this work, field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 2–7V were applied to a CoNi/Pt multilayered film fabricated on either bare silicon or oxidized silicon substrates. Different types of Ir/Pt and W STM tips were used in the experiment. The results show that thermally recorded magnetic marks are formed with a nearly uniform mark size of 170nm on the film fabricated on bare silicon substrate when the pulse voltage is above a threshold voltage. The mark size becomes 260nm when they are written on the identical film fabricated on an oxidized silicon substrate. The threshold voltage depends on the material work function of the tip, with W having a threshold voltage about 1V lower than Pt. A synthesized model, which contains the calculation of the emission current, the simulation of heat transfer during heating, and the study of magnetic domain formation, was introduced to explain experimental results. The simulation agrees well with the experiments. [Copyright &y& Elsevier]

• Formation of mm2 ordered Co 3 Pt is correlated to the in-plane ordering in the Co 50 Pt 50 layers. • In-plane structure can be enabled when lattice changes to orthorhombic cell with small b/a = 1.54. • An Imm2 structure is found to be stable compared to the previously predicted Pmm2 structure. • The ordering at the obtained lattice condition is sensitive to the composition. A lattice-based Monte Carlo model is used to investigate the ordering conditions necessary to produce the ordered Co 3 Pt phase (mm2). In this phase, Co and Co 50 Pt 50 atomic layers alternate along the c-axis of the parent hexagonal structure. It is found that perpendicular ordering where the Co and Co 50 Pt 50 layers alternates, is strongly correlated with in-plane ordering of the Co 50 Pt 50 layers. In these layers the Co atoms and Pt atoms form alternating rows in parallel. Such atomic ordering within the plane is only facilitated by a deformation of the hexagonal lattice such that the ratio between the atomic spacing transverse to the row and along the row, b/a , becomes significantly smaller and the structure becomes orthorhombic. At adequate lattice spacings and b/a ratio, both in-plane ordering and perpendicular ordering occur simultaneously. In addition, the Co 50 Pt 50 layers are also staggered alternately, forming a structure with the Imm2 space group. The ordered Co 3 Pt with Imm2 symmetry is also found to be sensitive to changes in the Pt composition. [ABSTRACT FROM AUTHOR]

• The moment of FeCo thin films decreases after oxidation. • Temperature is the dominant factor in the FeCo thin film oxidation. • The mechanism of the moment loss is due to the formation of ferrimagnetic oxide and the change of Fe/Co ratio in the remaining FeCo layer. • Co does not take part in the FeCo oxidation process. FeCo (60%-70% Fe, 30%-40% Co at.%) alloys have been used as write transducer materials due to their large saturation magnetization at room temperature (μ 0 M = 2.45 T). In this research, we investigate the influence of oxidation on the magnetic moment of a Fe 70 Co 30 material at elevated temperatures in the application of heat assisted magnetic recording. We find that the moment of Fe 70 Co 30 decreases after oxidation for all temperatures explored and that Co does not take part in the oxidation process. The moment loss is mainly due to the formation of ferrimagnetic Fe 3 O 4 or γ-Fe 2 O 3 as well as the change of the Fe/Co ratio in the FeCo alloy. A 2 nm Cr underlayer has been employed to change the FeCo texture from (1 1 0) to (0 0 2). This also increases the grain size of the FeCo thin film. In the case of the (0 0 2) textured sample, voids form between the FeCo film and the oxide layer, which could be the direct result of Fe cations diffusion. [ABSTRACT FROM AUTHOR]

Abstract: Superconducting quantum interference devices (SQUIDs) have been widely utilized in biomedical applications due to their extremely high sensitivity to magnetic signals. The present study explores the feasibility of a new type of nanotechnology-based imaging method using standard clinical magnetoencephalographic (MEG) systems equipped with SQUID sensors. Previous studies have shown that biological targets labeled with non-toxic, magnetized nanoparticles can be imaged by measuring the magnetic field generated by these particles. In this work, we demonstrate that (1) the magnetic signals from certain nanoparticles can be detected without magnetization using standard clinical MEG, (2) for some types of nanoparticles, only bound particles produce detectable signals, and (3) the magnetic field of particles several hours after magnetization is significantly stronger than that of un-magnetized particles. These findings hold promise in facilitating the potential application of magnetic nanoparticles to in vivo tumor imaging. The minimum amount of nanoparticles that produce detectable signals is predicted by theoretical modeling and computer simulation. [Copyright &y& Elsevier]