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Yttrium Iron Garnet Cores

IP.com Disclosure Number: IPCOM000098876D
Original Publication Date: 1958-Aug-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 32K

Publishing Venue

IBM

Related People

Calhoun, BA: AUTHOR

Abstract

Yttrium iron garnet cores subjected to a magnetic annealing treatment have extremely square hysteresis loops at liquid nitrogen temperature (-195 degrees C). The initial treatment of the oxides must be such that a high density core is obtained and it must be quenched very rapidly from the final firing temperature to room temperature. The dry-mixed oxide powders are calcined at 1300 degrees C and, after pressing, fired at 1430 degrees C and 1450 degrees C for four hours.

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Yttrium Iron Garnet Cores

Yttrium iron garnet cores subjected to a magnetic annealing treatment have extremely square hysteresis loops at liquid nitrogen temperature (-195 degrees
C). The initial treatment of the oxides must be such that a high density core is obtained and it must be quenched very rapidly from the final firing temperature to room temperature. The dry-mixed oxide powders are calcined at 1300 degrees C and, after pressing, fired at 1430 degrees C and 1450 degrees C for four hours.

The selected cores then are subjected to a large (25 to 40 oersteds) 60 cycle magnetic field and cooled by slowly lowering them into liquid nitrogen with the A.
C. field on. When the core reaches liquid nitrogen temperature, the current is slowly reduced to zero. Hysteresis loops obtained on subsequently applying a small A. C. current with the core maintained in liquid nitrogen are shown in above drawing. The switching speeds of these cores are slow (S(w) 40 oer. - microseconds). Slower cooling of the core materials from the firing temperature to room temperature results in garnet which has a less square hysteresis loop at low temperature but whose S(w) is about 1 oer. -microsecond.

The significance of the line observed at 8.3 oersteds, as shown in the drawing, is that, with that applied field, the material remains in one remanent condition. When the applied field is increased to 8. 8 oersteds the material assumes both remanent states and an open loop is obtained.

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