The oldest magnetic record in our Solar System identified using nanometric imaging and numerical modeling

Recordings of magnetic fields, thought to be crucial to our Solar System’s rapid accretion, are potentially retained in unaltered nanometric low-Ni kamacite (~metallic Fe) grains encased within dusty olivine crystals, found in the chondrules of unequilibrated chondrites. However, most of these kamacite grains are magnetically non-uniform, so their ability to retain four-billion-year-old magnetic recordings cannot be estimated by previous theories, which assume only uniform magnetization. Here, we demonstrate that non-uniformly magnetized nanometric kamacite grains are stable over Solar System timescales and likely the primary carrier of remanence in dusty olivine. By performing in-situ temperature-dependent nanometric magnetic measurements using off-axis electron holography, we demonstrate the thermal stability of multi-vortex kamacite grains from the chondritic Bishunpur meteorite. Combined with numerical micromagnetic modeling, we determine the stability of the magnetization of these grains. Our study shows that dusty olivine kamacite grains are capable of retaining magnetic recordings from the accreting Solar System

Patterned magnetic thin films for ultra high density recording

The areal bit density of magnetic disk recording has increased since 1990 60% per year and even in the last years 100%. Extrapolation of these rates leads to recording parameters not likely to be achieved without changes in the present way of storing hard disk data. One of the possible solutions is the development of so-called patterned magnetic media. Such media will also shift the superparamagnetic limit positively in comparison with the present thin film media. Theoretically, a bit density in the order of Tbits/in 2 may be possible by using this so-called discrete magnetic recording scheme. The patterned structures presented in this paper consist of a regular two-dimensional array of single domain dots with large uniaxial magnetic anisotropy and have been prepared from CoNi/Pt multilayers with strong intergranular exchange coupling and large perpendicular magnetic anisotropy. For the preparation of the patterned media, a patterning process based on Laser Interference Lithography method (LIL) and Ion Beam Etching has been developed. This technology provides the possibility to pattern 2-D arrays of submicron dots smaller than the critical size for the transition from multi to single domain. The smallest prepared dot sizes are 60 nm with a center-to-center dot spacing of 200 nm and thickness of 30 nm. The magnetic characterization of these dots showed that they are single domain with reasonable coercivity and good thermal stability. Micromagnetic simulations show that the single domain state is the lowest energy state for dots with a diameter below 75nm, which confirms the experimental observations