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(1)Rotatable Anisotropy in Films of Nickel By. Hiroshi KONNO DePartment of Phvsics (Received April 3. 0, 1964). Synopsis The nickel films which have been deposited at substrate temperature as low as room temperature possess the property of having a rotatable anisotropy. The anisotropy constant and rotational hysteresis loss vs. field were measured. by use of an automatic recording torque meter in the temperature range between room temperature and liquid nitrogen temperature. Considering the '. results, a domain configuration model for the rotatable anisotropy is presented.. gl. Introduction General magnetic anisotropy of ferromagnetic materials, that is crystalline anisotropy, induced anisotropy by the field-cooling, anisotropy by internal stress and magnetostriction, etc. is stable at room temperature and does not change its magnitude and direction by applying a magnetic field. But in the case of. thin magnetic films, many investigators observed a phenomenon that the anisotropy changes its direction by applying a field at room temperature, and it is named " rotatable anisotropy ".. T. MATcovicH et al.i) observed this phenormenon on the permalloy films which had been made by the thermal decomposition of nickel and iron carbonyls, and illustrated the phenomenon by a model of diffusional ordering of interstitial carbon atoms.. R.J. PRosEN et al.2) mentioned in their report that a nickel oxide layer on the surface of the permalloy film was essential for the existence of rotatable. anisotropy, and similar consideration of the effect was presented by C.D. GRAHAM et al.`) with use of the torque experiment on the oxidized nickel films.. Another suggestion for the rotqtable anisotropy has been given by S. LEHRER3), that is, magnetostriction and strain are resposible for the mechanism of the effect,. In the experiment described bellow, nickel films are measured by using an automatic recording torque meter, and the results suggest that existence of.

(2) 16 H. KoNNo. domains in which the magnetization has normal component to the plane of the. film is essential for the effect of rotatable anisotropy.. g2. Experiment and Discussion Nickel films have been deposited onto microscope cover glass substrates which have been cleaned carefully by ultrasonic wave and baked-out at appro-. ximately 4000C in a vacuum of,3×10-6mmHg before deposition. The films were deposited at various temperatures between room temperature and about 2000C for each run of deposition. The liquidTnitrogen trap was operated in the vacuum system from beginning to bake the substrates to finishing evaporation. The film thickness was distributed around 1000A.. All films whose substrates have been kept at room temperature during deposition possess the property of having a rotatable anisotropy; contrary to this, in the films deposited at a substrate temperature higher than 1000C no rotatable anisotropy is found･.. Torque curves for a typical rotatable anisotropy film (the substrate temperature is 300C, 1250A thick) measured at room temperature are presented in. a) c). geee. ".messssg. "eeewW. ma,. b). d) twas･･ee･･･ ss±me･. ee ec. ss. .mp, ,#x ,,ee,. gewaeswaee. Fig. 1.. The torque curves for a typical rotatable anisotropy'film of nickel,. of which the substrate temperature during'deposition was 150C,.

(3) Rotatable Anisotropy in Films of Nickel 17 Fig. 1. Every measurement of the torque curve was performed after the film had been saturated by applying a strong field in a direction in the plane of the. film. Fig. 1 a) is a torque curve which is measured in a field as low as the magnetization start to rotate, that is 400 Oe (in a field slightly lower than this, the curve is unidirectional). In the former half of field rotation, the torque behaves as if it were unidirectional sinusoidal, and in the latter half, it. almost disappears. As repeating the field rotation, the amplitude of the curve. decreases. Fig. 1 b); the curve measured in 640 Oe shows a large uniaxial anisotropy whose easy axis coincide with the direction of last saturation <in this figure, it is the origin of the angle), that is the rotatable anisotropy. As increasing the field, e. g. 840 Oe, the rotatable anisotropy decreases [Fig. 1 c)];. in 1250 Oe, by rotating the field, in this measurement, the easy axis of the rotatable anisotropy follows some angle behind the field; then, the uniaxial. term of the curve vanishes and only the rotational hysteresis remains. As further increasing the field, the magnetization bf the film approaches to saturation.. The uniaxial anisotropy constant Kh, and rotational hysteresis loss W. vs. field, which are observed in another film (the substrate temperature is 400C, and 1150Ao thick), are ploted in Fig. 2. According to this, the field is divided. 5.0. 40 xsd-d s,O. } .zs 2D. xlo5 ergled. uk------b+c-*'. fthx. o. Ku. e. Wr. (/. / A.)6e)s/. s ¥. Xo A.. d. x. l.O. o o. o-o-. e5t,---..-"e. IOOO 2000 5000 4000 5000 FIELD Oe. Fig. 2. The typical curves of the uniaxial anisotropy constant K. and rotationalhysteresis Ioss l77;･ for each radian vs. field, measured at. room. temperature.. into following four ranges using symbols of Hl., Hh. and Hk:where liL. and ll},, are fields inwhich the low-field peak and high-field peak of Mi. appears, respectively, and a, the threshold field Qf saturation. x. range (a): Iower than Mp (in this range the magnetization cannot be rotated, and thecurve is unidirectional),.

(4) 18. H. KoNNo. x,,. range (b): higher th･an H,, lower than Hh, (i'n this range, the rotatable amsotropy appears), range (c): higher than Hh,, lower than a (in this range, the rotatable anisotropy vanishes and only l?l7. remains),. range (d): higher than q (in this range, the easy axis of the rotatable anisotropy is perfectly oriented to the direction of applied field).. The field Hh, is a function of the substrate that is, it decreases rapidly with increasing high-field Peak overlaps to the low-field peak, table anisotropy is lost. The heat treatment of. temperature during deposition, the temperature. And when the the property of having a rotathe specimen is also effecitive. to lower the lilh,. (a) 5.0. ×io5erg/cms C･""h'Nh. N,,. 4,O v' e. o. Ku. e. Wr. s>. i; 5,O. x. o. 2.0. /o-'. oo. ,,d ,. o. eXXX. I,O o. '. o o. 1OOO. 2000 5000 4000. 5000. FIELD Oe. (b) ×Eo5 ergfems. 5.0. '4.0. o/ /. Ne. rd d 5.0 Nill. ) 2,O. di. ,il. 8. /. l.o. o. Ku i. e. Wr. e'-hhe. ×.e-.ee. cK･o. -. eN. o D. 1OOO. 2000 5000 4000 5000. FIELD Oe. Fig. 3.. Bihaviors of K, and 17I7;- at low temperatures,. (a) at -70oC, (b) at ----195oC..

(5) RotatableAnisotropyinFilmsofNickel :･ 19 If a sort of crystalline structure such as the directional ordering of atomic. pairs were the cause of the effect of rotatable anisotropy, its constant at the. liquid-nitrogen temperature shouid be different from that of at room temperature. The temperature dependence of the rotatable anisotropy and J7V7. is studied, but considerable change is not observed even at the liquid-nitrogen temperature, as shown in Fig. 3. The time required to rotate the easy axis, even at the liquid-nitrogen temperature, is several seconds at the longest,. although exact measurement has not been performed. These facts suggest that the directional ordering mechanism is not the origin of the rotatable. anlsotropy. ' .. '. GRAHAM4) reported that the rotatable anisotropy in'nickel films on glass had appeared only after they had been allowed to oxidize, and it had vanished at the N6el point of NiO, about 2500C. Because of this, he concluded that the. rotatable anisotropy was associated with the antiferromagnetic NiO. This model is dithcult to illustrate the present result that the variation of the substrate temperature during deposition, keeping other conditions constant, is effective to control the appearance of the rotatable anisotropy in the nickel films on glass.. According to another study by the present author,5' nickel films which are deposited at a low substrate temperature have a so large uniaxial anisotropy with its easy axis perpendicular to the film-plane, that these films devided into domains in which the magnetization directed perpendicular to film-plane. Considering the condition of sample preparation (low substrate temperature),. rotatable anisotropy films are also the film having these domains. We can consider, in conclusion, as follows; that when a rotatable anisotropy film is at first saturated along a direction in the film-plane, and when the applied field. decreases to one of range (b); then the film must be devided into domains in which the magnetization has the component perpendicular to the plane of the. film (at an angle ±a with the plane of the film). As rotating the field, in. the process of torque measurement, magnetization in each domain moves without deformation of the domain configuration established by the above process. This will be the cause of the appearance of the rotatable anisotropy. Recently N. SAiTo, H. FuJiwARA and Y. SuGiTA6) have reported the observation of these domains.. Acknowledgement The author deeply indebted to members of the department for their helpful discussions. Thanks are also due to Mr. Y. TERui and Mr. K. OGAwA for their assistance during this experiment. This investigation was partly supported by the Scientific Research Funds from the Ministry gf Education..

(6) 20 H. KoNNo References 1) T. MATcovicH, E. KoRosToFF and A. ScHMEcKENBEcHER: J. Appl. Phys, 32 (1961),93S. ･ 2) R.J. PRosEN, J.O, HoLMEN and B.E. GRAN: J. Appl. Phys. 32 (1961), 91S. 3) Sherwin S. LEHRER: J. Appl. Phys. 34 (1963), 1207. 4) J. M. LoMMEL and C.D. GRAHAM, Jr.: J. Appl. Phys. 33 (1962), 1160. 5) H. KoNNo and Y. GoND6: in this issue of Sci. Rep. Yokohama Nat. Univ. 6) N. SArro, H. Fu.JiwARA and Y. SuG[rrA: J. Phys. Soc. Japan, 19 (1964), 421. '.

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