High Bias Field Research Articles

Drastic modifications of electrical properties of ferroelectric crystal plates with thickness, the case of triglycine sulphate

The electrical properties of triglycine sulphate (TGS) single crystal plates are completely modified when the thickness is decreased down to 1 μm. The dielectric constant at the Curie temperature T0 is reduced by two orders of magnitude, coercive field is increased in the same ratio, and hysteresis loops are observed at several degrees above T0. Phenomenologically these observations can be explained in the frame of Devonshire's theory by assuming an internal electric bias Eb ≃ 1 MV/m for the thinnest plates.To explain such a high bias field we have been led to a tentative model with a surface layer where spontaneous polarization is smoothly decreasing from the bulk value PSB to a finite one PSB at the crystal surface. It is in this layer that a high polarizing field is calculated at room temperature. Its values may be slightly reduced when free charges of opposite sign are assumed to be injected by each electrode (Schottky barriers). These free charges will partially stay when temperature is raised above Curie point and lead to a polarizing field in the bulk which could explain the observation of hysteresis loops above the Curie temperature T0. There is, however, experimental evidence that such a dc bias field is small. The spontaneous polarization observed above T0 is finally ascribed to the contribution of surface layers and is a proof that their Curie point is higher than T0.

An Al-stabilized Nb<inf>3</inf>Sn pulse coil

A pulse coil has been designed and manufactured that generates a pulse field of 1T/0.1sec in a high bias field (∼12T). The coil is to be used for the measurements on superconducting conductors. It is wound by an Al-stabilized multifilamentary Nb 3 Sn conductor on a FRP bobbin, and consists of two concentric coils arranged to reduce leak field in the outer bias coils. The coil was shown to be stable in repeated pulse operations. Its loss was measured and discussed.

AC Loss in the Coil of a Nonideal Type 2 Superconductor. I. A Row of Wires in a Transverse Magnetic Field

A theoretical expression for the AC loss of the row of wires of nonideal type 2 superconductors in a transverse AC magnetic field is derived with the aid of the critical-state model. The applicability of the present calculation is limited to the so-called semi-quasistatic AC loss of the wires with a pinning force of the Bean-London type in a high DC bias field. Compared with the usual simple slab approximation for a coil, a striking difference is found in some cases with regard to the flux penetration and the value of the AC loss.

Dynamics of magnetic domains in microwave fields

Using special microwave structures, strong spin precessions can be excited locally in LPE garnet films by microwaves near the ferrimagnetic resonance frequency. As soon as the precession angle θ exceeds a critical value, the spins tip over creating a bubble domain. If the bubble is small compared with the excitation region, it is ejected out of this region along a spiral path. In the other case, the bubble is trapped at the excitation region and reaching another critical value of θ the spins again tip over, creating a ring domain. Single-ring domains can only be stabilized by the microwave induced spin precession inside the ring. Amplitude modulation of the microwaves leads to a corresponding radial oscillation of the ring. Stripe domains are forced to align either parallel or perpendicular to the gradient of the spin precession. At high bias fields a new type of domain is observed.

Long-term testing of 68 kbit bubble device chips

Long-term testing of the data reliability has been done on 68 kbit bubble device chips of a serial shift register design. The chips were fabricated using LPE garnet of the YSmLuGeCa composition with 3 micron strip-width. The bubble propagation structure contained a single permalloy element per 16 micron period. Testing was done at 50 kHz and 40 Oe rotating field over a chip temperature range from 30°C to 100°C. The data show that such chips have at least 15 Oe of bias field margin with an error probability of less than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3 \times 10^{-14}</tex> per bubble per cycle of rotating field, although this margin can be reduced by chip defects. Preliminary results indicate that the operating parameters of the chip have a significant impact on the error rate. An investigation of bubble propagation, separated out from the other bubble functions, shows that the propagation error rate near the high bias field limit decreases more rapidly than exponentially with decreasing bias field.

Microwave Anisotropy and Frequency Dependence of Hot Electron in n-Type Gaps

The physical mechanism of the microwave anisotropy due to the hot electron effect in a semiconductor bulk is at first investigated phenomenologically for the case that a relative spatial angle θ between a small microwave electric field and a high intensity electric bias field is arbitrary. And then, the microwave anisotropy and the frequency dependence in n-type GaAs are analyzed by using the Boltzmann transport equations. Conclusively, the microwave anisotropy is especially remarkable in the region of negative resistance. Furthermore, as an interesting result, the dependences of both the microwave angular frequency ω and the angle θ in the microwave characteristics are monistically determined by only one factor \\varOmega≡ω/cos θ under the proper condition of ωτ (τ: relaxation time), which is satisfied in the region of negative resistance.

LSA oscillator waveforms for high efficiency

The efficiency of an LSA oscillator can be increased by adding the second harmonic for dc bias electric fields up to 12 kV/cm. For higher bias fields, a third-harmonic content seems to be preferable. With second harmonic present, 30 percent efficiency appears possible at 11 kV/cm dc bias.