Masaru Mikami

Double torsion testing and finite element analysis for determining the electric fracture properties of piezoelectric ceramics

This paper presents the results of an experimental and numerical investigation in electric fracture behavior of composite [Pb(Zr,Ti)O3] double torsion (DT) specimens. DT tests were conducted on a commercial piezoelectric ceramic bonded between two metals. Fracture loads under different electric fields were obtained from the experiment. Nonlinear three-dimensional finite element analysis was also employed to calculate the energy release rate for DT specimens based on the exact (permeable) and approximate (impermeable) crack models. The effects of applied electric field and domain switching on the energy release rate are discussed, and the model predictions are compared with the results of the experiments.

Improvement of magnetic and R/W properties in longitudinal media by using CrX/Cr dual underlayer

The effect of in-plane lattice matching on the magnetic and read/write properties has been quantitatively studied in CoCr/sub 24/Pt/sub 12/B/sub 4/ or CoCr/sub 20/Pt/sub 8/Ta/sub 4/ media grown on Cr, CrMo/sub 20/ and CrMo/sub 20//Cr underlayer. It is found that by using CrMo/sub 20/ (5 nm)/Cr (5 nm) dual underlayer, significant improvement of magnetic and R/W properties are realized. It is clarified that: (1) the utilization of CrMo/Cr dual underlayer increases H/sub c/ mainly due to the improvement of in-plane crystallographic orientation; (2) the lattice misfit has a small effect on the improvement of in-plane crystallographic orientation. The improvement of in-plane crystallographic orientation by using CrX/Cr dual underlayer is suggested to be due to lattice strain at the interface of Cr and CrX underlayer, which enhances the grain growth of the magnetic layer.

Electroelastic Fracture Mechanics of Piezoelectric Layered Composites

This paper develops a theoretical electroelastic fracture mechanics for piezoelectric layered composites. A piezoelectric layer bonded between two elastic or piezoelectric materials containing a crack normal to the interfaces is considered. The ends of the crack are situated at equal distances away from the interfaces. Both analytical and simulation methods are formulated to determine the effects of applied electric field and polarization switching on the fracture mechanics parameters such as stress intensity factor, energy release rate, and energy density factor. The results for the exact (permeable) and approximate (impermeable) boundary conditions are presented in graphical form.

Study on increasing the coercivity of CoCrPtB media with high Pt content

The dependence of magnetic properties and microstructure on the composition of CrMox (x=0–40 at. %) underlayer and CoCr-based nonmagnetic interlayer has been examined for CoCr18Pt20B4 longitudinal media. In the media using a single CrMo (10 nm) underlayer, the highest coercivity that can be obtained is only 1.9 kOe. The coercivity is drastically increased up to 5.0 and 6.4 kOe by using substrate/Cr (5 nm)/CrMo (5 nm) dual underlayer and substrate/CrMo (10 nm)/CoCr38Mo2 (1.3 nm), respectively. It is clarified that the improvement of the coercivity is mainly due to the enhancement of the quality of the crystal growth of the magnetic layer, which results in the improvement of magnetocrystalline anisotropy field and in-plane crystallographic orientation.

Magnetic grain size reduction by using oxygen exposure process onto very thin islandlike WCr seedlayer in longitudinal recording media

To reduce the grain size and the media noise in CoCrPtB/CrMo longitudinal media, a sputtering process which includes the exposure of oxygen onto the surface of a very thin (0.5 nm) WCr50 seedlayer has been developed. The purpose of oxygen exposure onto the seedlayer surface is to enhance the nucleation sites of the seedlayer. It is found that (a) the exposure of 25 and 100 L (1 L corresponds to the adsorption of one layer of the oxygen atom when the sample is exposed to oxygen atmosphere) of oxygen onto the seedlayer reduces the mean grain diameter of the magnetic film from 8.3 to 7.5 and to 7.0 nm, respectively, (b) the exposure of 25 and 100 L of oxygen onto the seedlayer decreases the media noise by 15% and 45% and improves the media signal to noise ratio by 1.5 and 5 dB, respectively.

Dependence of thin film media microstructure and recording properties on composition of Cr-based very thin seedlayer

Summary form only given. Recent studies have shown that WCr seedlayer with the thickness of about 1 nm is effective to reduce both the grain size and the media noise in longitudinal media. It is considered that the very thin seedlayer forms an island-like structure which increases the nucleation sites density of the substrate surface. Since the initial growth form of the seedlayer strongly depends on the melting point of the seedlayer, it is essential to study the effect of the melting point of the seedlayer on the media properties. We study the dependence of the microstructure, magnetic and R/W properties on the melting point of very thin Cr-based seedlayer to clarify the design guidelines for media using such a kind of seedlayer. The media were deposited onto textured NiP/Al substrates. After heating the substrate up to 250/spl deg/C, deposition of 0.5 nm seedlayer, dry etching treatment with Ar gas and deposition of 10 nm CrMo/sub 15/ underlayer, 20 nm CoCr/sub 24/Pt/sub 12/B/sub 4/ magnetic layer and 7 nm C protective layer were performed successively. The melting point of the seedlayer was varied from 1600/spl deg/C to 3400/spl deg/C by using various materials such as Cr/sub 85/Ti/sub 15/, Cr, W/sub 25/Cr/sub 75/, W/sub 50/Cr/sub 50/, W/sub 75/Cr/sub 25/ and W.