Y. Kondo

Fabrication of [001] L10-FePtRh ferro-antiferromagnetic pattern by flat-patterning method

A flat-patterning method that exploits the ferromagnetic (FM) – antiferromagnetic (AF) transition in [001]-oriented L10 FePt1-xRhx films was investigated. FM–AF patterns with dot diameters between 15 and 1000 nm were fabricated by locally diffusing a small percentage of FePt atoms onto the FePt1-xRhx film. The geometric and magnetic properties of the patterns were analyzed in detail. Only the area whose composition crossed the FM–AF threshold underwent a magnetic phase change to the FM phase. FM dots with single-domain structures were observed in the AF matrix in the range of 15–100 nm by magnetic force microscopy.

Study on nanoscale patterning using ferro-antiferromagnetic transition in [001]-oriented L10 FePtRh film

A bit patterning process using the ferromagnetic (FM)-antiferromagnetic (AF) transition in [001]-oriented L10 FePt1-xRhx films was investigated. First, the composition (x) dependence of magnetization (Ms) and magnetocrystalline anisotropy (Ku) of the films was studied. The films with 0u2009≤u2009xu2009≤u20090.32 showed ferromagnetism (800u2009≤u2009Msu2009≤u20091100 emu/cm3) with a high magnetocrystalline anisotropy (1.7u2009×u2009107u2009≤u2009Kuu2009≤u20097.0u2009×u2009107 erg/cm3), and the films with 0.34u2009≤u2009xu2009≤u20090.40 showed antiferromagnetism. The composition of xu2009=u20090.34 was the threshold of the FM-AF transition. Next, the FM-AF transition was applied for bit patterning. Atomic diffusion was used for modifying the composition. Only the magnetic phase of the area whose composition crossed the threshold changed abruptly to the FM phase. FM dots with sizes (D) of 20u2009≤u2009Du2009≤u20091000 nm were observed in the AF matrix by magnetic force microscopy. The dots with Du2009>u2009100 nm formed multidomain structures, and the dots with Du2009≤u2009100 nm formed a single-domain structure.

Fabrication of dot pattern using magnetic phase change on Pt ion-implanted L10 FePtRh film with high magnetocrystalline anisotropy

Phase change from ferromagnetic to nonmagnetic phase by ion implantation was investigated for bit patterning. An antiferromagnetic L10 FePt0.64Rh0.36 film was implanted with Pt ions at 6.0u2009×u20091015 ions/cm2 in order to control its magnetic properties. The film changed to a ferromagnetic one, with the (001) crystalline texture being normal to the film plane and a magnetocrystalline anisotropy of 2.3u2009×u2009107u2009erg/cm3 in the perpendicular direction. Using this magnetic phase change, a planar dot pattern was fabricated. The average height between the dots and the spacing was 0.35u2009nm, and ferromagnetic dots 50u2009nm in diameter were observed.

Ferromagnetic-Paramagnetic Patterning of FePtRh Films by Fe Ion Implantation

The crystalline and magnetic properties of 6.12 nm thick Fe_x(Pt_0.68Rh_0.32)_100-x films with 50.0 ≤ x ≤ 64.3 and a potential bit-patterning process that utilizes the FM-PM transition caused by Fe ion implantation were investigated. At room temperature, for 50.0 ≤ x ≤ 55.9 the films were ferromagnetic (FM), with an L1₀ phase, whereas for 57.9 ≤ x ≤ 64.3 the films were paramagnetic (PM), with an phase. This composition dependent FM-PM transition forms the basis of a bit-patterning process in which, at first, micro-fabricated resist masks were prepared on the (ferromagnetic) Fe₅₀ (Pt_0.68 Rh_0.32)₅₀ film. Implantation of Fe ions at a dose of 9 × 10¹⁵ ions/cm² then results in an increase of x in the implanted areas, from 50.0 to 58.3. After annealing, 300 nm FM dots were observed by magnetic force microscopy, which confirmed that only the implanted areas had changed from FM to PM and that the dot areas had remained in the FM phase with the L1₀ structure.

Development of microscopic magnetometer with reflective objective using magneto-optical Kerr effect

A microscopic magnetometer using magneto-optical Kerr effect (MOKE) was developed to characterize the magnetic properties of hard magnetic nano-structures such as a bit-patterned medium and a magnetoresistive random access memory. Our new type magnetometer has a unique feature that adopts the reflective objective instead of the generally used refractive lens to reduce the unnecessary rotation of polarization axis of the light by the lens with Verdet constant in a magnetic field. A Schwarzschild-type objective consisting of two spherical mirrors was applied as the reflective objective in our magnetometer. The objective was designed specifically for our magnetometer. An actual focusing spot diameter at the sample surface was estimated to be 4.7u2009μm by the knife-edge measurement. Furthermore, a magnetization curve was measured by MOKE for the Co80Pt20 thin-film line with a width of 75u2009μm, and demonstrated that our magnetometer can reduce the unnecessary rotation of polarization axis compared with the one meas...