Robert Douglas Hempstead

Low‐coercivity amorphous magnetic alloy films

It is well known that rapidly quenched bulk samples of amorphous transition‐metal–metalloid alloys can be made with high permeability and low coercivity; however, little is known of the magnetic properties of these alloys when prepared by thin‐film‐deposition techniques. Sputter‐deposited films of iron‐carbon, iron‐silicon‐boron, iron‐chromium‐phosphorus‐carbon, cobalt‐iron‐boron, and cobalt‐iron‐chromium‐phosphorus‐boron have been prepared, and it is shown that these films can be made with low coercivity and high saturation magnetization by proper choice of deposition conditions. The magnetic properties of iron‐carbon films were found to depend on the sputtering conditions, in particular on the argon‐gas pressure. At an argon‐gas pressure of 15 μm, films with 70 at.% iron and 30 at.% carbon were obtained with a 4πMs of 12 000 G and coercivities in the range 0.1–0.9 Oe. Films made with higher and lower argon‐gas pressure had significantly higher coercivity. Other alloys were prepared to explore corrosion ...

Thermally induced pulses in magnetoresistive heads

The thermal response of a magnetoresistive head is analyzed for frictional heating between the head surface and dust particles or other asperities on the recording medium surface during relative motiono f head and medium. A theoretical model is presented showing that pulses are induced in the output of a magnetoresistive head as a result of this frictional heating. The model predicts the dependence of these thermal noise spikes on the thermal properties of the substrate and cover chip for the magnetoresistive head, the dimensions of the magnetoresistive stripe, the head-medium relative velocity, and the rate of frictional heat generation. Experimental verification of the theoretical model is obtained by scanning a focused laser beam across a head.

Steady‐state and transient heating of narrow conductor lines on garnet substrates

Calculations are given of the steady‐state thermal conductance for narrow conductors on garnet substrates, as found for control lines of bubble circuits. The transient heating of these lines is also analyzed and they are found to have rise times in the microsecond range.