Yoshihiro Shiroishi

Ferroelectricity in {N(CH3)4}2ZnCl4

Tetramethylammonium tetrachlorozincate, {N(CH 3 ) 4 } 2 ZnCl 4 has been found to undergo successive phase transitions at about -112, -92, 3.3, 6.0 and 20°C and to show ferroelectricity along the a axis in the temperature range between 3.3 and 6.0°C.

Ferroelectricity in NH4LiSO4

It has been found that in NH 4 LiSO 4 another transition point 186.5°C exists in addition to the already known one 10°C and this substance is ferroelectric between these two transition points. Anomalies of dielectric constant at the transition points are very small as compared with those of proper ferroelectrics. The Curie-Weiss law holds within a narrow temperature range in the phase above the upper transition, where the Curie constant has a very small value of 5.6 K. Moreover the spontaneous polarization shows a curious increase with lowering temperature. Thus NH 4 LiSO 4 can be said to be one of improper ferroelectrics.

Magnetic properties of multilayered Fe‐Si films

The coercivity and permeability of Fe‐Si films can be improved by laminating several layers with either nonmagnetic (SiO2, Al2O3, Al or Mo) or ferromagnetic (Ni, Fe, Co or 20‐wt. % Fe–Ni) spacers. It is also found that films made with soft magnetic laminations have an advantage over nonmagnetic or hard magnetic ones. Such behavior is concluded to be attributed to the smaller grain size, and pinhole or exchange coupling of multilayered Fe‐Si films by observing domain and grain structures.

Ferroelectricity in RbLiSO4

In RbLiSO 4 , dielectric measurements and microscopic observations have revealed successive phase transitions at 166, 188, 202 and 204°C with rising temperature. Ferroelectricity has been found along the a axis in the phase between 166 and 188°C. Further a ferrielectric behavior is found in this phase, when a field higher than about 20 kV/cm is applied.

Ferroelectricity in Rb2ZnBr4

Rb 2 ZnBr 4 has been found to show phase transitions at about -86 and 18°C, respectively and to be ferroelectric in the a direction below -86°C.

Effects of hydrostatic pressure on the successive phase transitions in ferroelectric {N(Ch3)4}2 CoCl4 and {N(CH3)4}2ZnCl4

Abstract The hydrostatic pressure effect on the stability of I, II, III, IV and V phases in {N(CH 3 ) 4 } 2 CoCl 4 is found to be quite similar to that of the corresponding I, II, III, VII and IV phases in {N(CH 3 ) 4 } 2 ZnCl 4 ; the ferroelectric phase III disappears at 600 bar for Co-salt and at 1150 bar for Zn-salt, and a new phase VII in Zn-salt induced by pressures above 400 bar corresponds to the phase IV in Co-salt which has already appeared at 1 atm.

X-Ray Studies on Successive Structural Transitions in RbLiSO4

Space groups and super-lattice structures of five phases of RbLiSO 4 are investigated by X-ray diffraction method. Phase I ( T >204^° C ) is paraelectric ( Pmcn - D 2 h 16 ). The incommensurate phase II (202< T <204^° C ) is characterized by a wave number k z =(2+δ)/5 with δ( T )=0.013(204^° C ) ∼0.137(202^° C ). Phase III takes c =2 c 0 structure which belongs to P 2 1 / c 11- C 2 h 5 , where c 0 is the cell dimension in phase I. The ferroelectric phase IV (166< T <185^° C ) belongs to P 11 n - C s 2 and takes c =5 c 0 super-structure. The I-II transition is 2nd order and the critical exponent is β=0.36 ±0.05, while other three transitions are 1st order ones.

Magnetic properties and read/write characteristics of Co‐Cr‐(Pt,Ta)/ (Cr‐Ti,Cr) thin film media

A Cr‐Ti underlayer is found to enhance the in‐plane coercive forces of Co‐Cr‐Pt and Co‐Cr‐Ta films; the maximum coercive force was 3.5 kOe for (CoCr0.15)0.84Pt0.16/CrTi0.2. The crystallites of Cr‐Ti grow in a more highly oriented and uniform manner than ones of Cr, and their lattice spacings are closer to those of Co alloys than Cr, improving the epitaxial growth of Co‐alloy crystallites with c‐axis in‐plane oriented components on the Cr‐Ti underlayer. The crystalline anisotropy constant of Co‐Cr‐Pt with a high Pt concentration is found by torque measurement to be larger than that of Co‐Cr‐Ta. These can produce extremely high coercive forces in Co‐Cr‐Pt/Cr‐Ti. The C/Co‐Cr‐Pt/Cr‐Ti thin film media with high coercive forces show excellent read/write characteristics; the linear densities at 50% signal drop are very high, 175 and 101 kFCI, for the C/Co‐Cr‐Pt/Cr‐Ti media at head‐to‐magnetic layer spacings of 0.01 and 0.07 μm.

Perpendicular magnetic recording and reproducing thin film head

A perpendicular magnetic recording and reproducing thin film head of a structure excellent in magnetic characteristics and easy of fabrication, wherein a lower magnetic layer disposed on a flat nonmagnetic substrate is used as a main magnetic pole, a first insulator layer is formed on the main magnetic pole, a conductor for a coil and a second insulator layer are disposed on the first insulator layer, and an upper magnetic layer which lies in contact with the lower magnetic layer through the first insulator layer at one end thereof and directly at the other end thereof and which overlies the second insulator layer in a part thereof other than both the ends is disposed and used as an auxiliary magnetic pole.

Experimental Studies on Ferrielectricity in RbLiSO4

Successive phase transitions in RbLiSO 4 at about 166, 185, 202 and 204°C have been investigated by an improved high-sensitive DTA, a differential scanning calorimetry and an automatic measurement of dielectric constant. Temperature- and field-dependences of 50 Hz D-E hysteresis loop are studied in detail. In the phase between 166 and 185°C, a triple hysteresis loop due to ferrielectricity is ascertained.