An Array of Ferromagnetic Nanoislands Nondestructively Patterned via a Local Phase Transformation by Low-Energy Proton Irradiation

Abstract

Low-energy proton irradiation was applied to pattern an array of metallic, ferromagnetic nanoislands through the local phase transformation of an oxidic, paramagnetic phase in a complex superlattice composed of repetitions of an oxidic and metallic layer. The irradiation inflicted minimal damage on the structure, resulting in the absence of unwanted defects and side effects. This nondestructive pattern transfer was clearly confirmed by the contrast between irradiated and unirradiated regions in electrical, chemical, and magnetic images. Simulation based on the magnetic properties suggests that this low-energy proton irradiation can nondestructively pattern an array of ferromagnetic islands with 8.2 nm in diameter and 7.4 nm in spacing between islands, which means it can achieve an areal density of ∼3 Tb/in.(2) with a thermal stability of over 80 kBT. Such an array is strong enough to overcome the so-called superparamagnetism limit in magnetic recording. The attributes demonstrated here corroborate that proton irradiation can be applied to design and pattern devices on a nanometer scale not only for magnetic but also for electric and optical materials systems in all such systems in which a local phase transformation is available.

Spectral properties of superconductors with ferromagnetically ordered magnetic impurities

“…Assuming a quadratic energy dispersion of electrons in the normal state and taking their effective mass equal to the bare electron mass, we can estimate that for a superconductor with Fermi energy E F 10 eV, the typical size of an impurity is ∼ 1 − 8 nm, and its magnetic moment M ∼ 8.5 × 10 4 µ B (for u S = 1). This coincides with the typical size of small ferromagnetic islands used in modern experiments 13,77 . On the other hand it justifies our treatment of the impurity spins as classical 78 .…”

Effect of Proton Irradiation on the Magnetic Properties of Antiferromagnet/ferromagnet Structures

“…Upon exposure to a proton beam of 5 × 10 14 ions/cm 2 , the magnetization is reduced to ~70% of its original value. The reduction of saturation magnetization was also observed in Co/Pd multilayer [12], when it was exposed to a proton beam of a few hundred eV. It was explained that the reduction of magnetization is due to the incorporation of the hydrogen in the magnetic layer [14], where the hydrogenation of the transition metals of Fe, Co, Ni causes the reduction of saturation magnetization by modification of the electronic structure.…”

“…The exchange bias is increased by a postannealing step, most likely due to the enhanced interfacial structures. A recent report demonstrates that proton irradiation can modify the magnetic property of FM/nonmagnetic samples of Co/Pd multilayer structures [11,12]. The proton irradiation to the CoO/Pd sample causes the reduction of the CoO to become a metallic Co, thus develop- In this study, we utilize proton irradiation on an AFM/ FM bilayer and investigate its effect on the magnetic properties of the exchange bias and on the magneto-thermoelectric properties.…”

Study on Proton Radiation Resistance of 410 Martensitic Stainless Steels under 3 MeV Proton Irradiation

“…However, the radiation effects on the magnetic properties of the 410 stainless steels, which are crucial for the application of 410 stainless steels in the in-vessel magnetic cores, are not investi- In this work, we have investigated the effects of proton irradiation on the magnetic properties of 410 stainless steels in order to understand the correlation between irradiation damage and magnetic property degradation. Proton irradiation was used to simulate neutron irradiation since it imparts same damages as neutron irradiation and also can provide short irradiation time and high damage rate [9,10]. And also, the penetration depth and transmutation in proton irradiation is very less [11,12].…”