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Usmanov N.N., Volf N.V, Starokurov Yu. V. , Buyda A.V., Saletsky A.M.

Moscow State University, Russia

MAGNETIZATION REVERSAL IN GARNET FERRITE FILMS

 

 In this work, the garnet films with orientation (210) were studied. The investigated samples have the angle of slope of the easy magnetization  axis in respect to the normal to the surface of the film 1) Q=30°, 2) Q=46°, thickness h=13 mm and h=11 mm, spontaneous magnetization MS=5 Gs and MS=3.4 Gs accordingly. The domain structure was observed at the magnetooptical unit by means of  Faraday effect. The samples brought to saturation state by the constant bias field HS=22 Oe and HS=18 Oe for the first and second samples respectively.

Fig.1.The dependencies 1-w(tf/Hz),     . Fig.2. The dependencies 1-w(tf/Hz) 2- td(tf /Hz) for the sample 1.                          2-td(tf/Hz) for the  sample 2.

 

The bias field was perpendicular to the surface of the film. The remagnetization of the films done by the impulse linear increasing field Hz with frequency 1 kHz. The field Hz had opposite direction to the bias field. The speed of increasing of this external field Hz was varied. We observed the delay of the start of the remagnetization process registered by photomultiplier relatively to the start of the external field impulse. The dependencies of the photoresponse delay td on tf/Hz are shown in fig.1,2.

The domains of the opposite directed magnetization appearance in the different summary external fields H0 if the steepness of the impulse was varied. The values of the summary field H0 are shown by light and dark rounds for the 1-st and the 2-nd films respectively in fig.4. Light and dark triangles corresponded to the values of these fields were obtained by high speed  laser photography technique. In this case the single rectangle impulse of external field Hz was applied. The samples from saturation state brought to the another saturation state under the action of impulse magnetic field Hz .The appearance opposite directed domains during back front impulse are tested visual by high speed photography.

 

 

Fig.3.

 

We observed the hysteresis loops for the investigated films using the rectangle impulses followed with frequency 1 kHz. The steepness of the increasing of the impulse field Hz was varied. Bias fields HS were constant.

The hysteresis loops for both samples transformed from quasi-static form to rectangle when the steepness was increasing up to 50 Oe/ms. The form of the loops is shown in fig.3. of external field for the opposite oriented domain appearance time are shown in fig.1,2. The minimal energy density corresponds to shift from remagnetization by movement of end domain wall and remagnetization by increasing of strippe domains.

Fig.4. The dependencies H0(/H) for both samples. Triangle marks accords to the data obtained  byhigh speed photography.

For small steepness of increasing of the external field the remagnetization process starts when the value H0 approaches to the value H0 in case of quasi-static remagnetization . The field H0 can be greater than saturation field if the external field has the great steepness of the increasing. The areas of hysteresis loops enlarge many times. The energy losses increase.

 

REFERENCES

1. Randoshkin V.V., Saletsky A.M., Usmanov N.N. Relaxation under Pulsed Magnetization Reversal of monocrystalline Films of (Bi,Lu)3(Fe,Ga)5O12 with orientation (210). Physics of the Solid State, v.44(4), 2002.

2. Usmanov N.N.., Ilicheva E.N., Shishkov A.G. The investigation of the motion of domain walls in ferrite-garnet films with orientation (210). Vestnik Mosk. Univ. Physics  Astronomy, v.36(5), 1995.