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The correlation between magnetic anisotropy and magnetoimpedance has been studied in field- and stress-annealed Fe73.5Cu1Nb3Si13.5B9 ribbons. As-cast and previously nanocrystallized samples were submitted to different annealing conditions (T=500, 530, and 560 °C and tensile stress σ=150 MPa) in order to induce different magnetic anisotropy. The magnetoimpedance ratio [ΔZ/Z] was measured at 3 MHz using a driving current Irms=10 mA. An hysteretic behavior of the magnetoimpedance ratio is observed. This hysteretic behavior is interpreted considering the magnetization process for samples exhibiting different magnetic anisotropies.

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Absfracf-Stress-annealed nanocrystalline FeCuNbSiB ribbons show correlation between induced magnetic anisotropy and magnetoimpedance. Two types of crystallization process were used in order to induce a transverse magnetic anisotropy: the first one was performed submitting the original amorphous samples to an applied tensile stress of a=150 MPa. In the second one, samples are nanocrystallised in a first stage and submitted to stress annealing at ~2 9 0 M P a afterwards. The maximum of the magnetoimpedance can be obtained for de fields larger than the anisotropy field of the sample or close to the irreversibility field. This behavior can be explained based in the simultaneous switching of two different magnetization processes taking place in the samples with high transverse magnetic anisotropy.Index Terms-Magnetization processes, magnetoimpedance, nanocrystalline ribbons, induced magnetic anisotropy. LINTRODUCTIONAs recently shown, soft magnetic materials exhibit the socalled giant magnetoimpedance (MI) effect [I-21, which consists in field-induced variation of its impedance through changes in the classical skin depth 6 and magnetic circular permeability p+ when a high frequency current flows through the magnetic conductor. In this framework, the frequency dependence of the MI value can be very informative due to the relation G=(p/7~p$)'~, where p is electrical resistivity and f is the frequency of the alternating, ac current. MI effect is sensitive to the anisotropy of the material [3-4]. On the other hand it is well known that suitable annealing of amorphous FeCuNbSiB ribhons under mechanical stress leads to nanoscale grain structure formation and induces a magnetic anisotropy whose easy magnetization axis is transverse to the direction of the tensile stress [5]. Some results on the MI effect in stress-annealed FeCuNbSiB ribbons were presented recently [4]. The ultrafine grain structure and the induced Mnnuscript received February 25,1999, revisedMay 10, 1999 M. Vizquez, (+34) 91-630 1724, fax (+34) 91.630 1625, mvazque@enfe.cs; G.V. Kurlyandskaya, (+34) 94.601 25 54, fax (+34) 94-485 8139, gnlina@we.lc.ehu.es, pmmnent address: ln&tute of Metal Physics UD RAS, Kovnlevskaya s t r 18, 620219 Ekntorinburg, Kussia, present address IWwrsidnd del Pais Vasoa UPV-EHU, Depto. Elwtricidnd y Eleotmnica, Aptdo. 644, 48080 Bilbao, Spain, J.P. Shocker, present nddresses: Instihlto de Fisica Uniwrsidnde Federal do Rio de Jnnoim C.P. 68528: 21945470 -Rio de,Janoiro -RI, Brasil. This work wns supported by The Basque Government, The Brazilian Agency FAPERJ, and The Sponish CICYT.magnetic anisotropy depend critically on the annealing conditions and the MI effect can be used as a probe to obtain information on the differentmicrostructural and anisotropy states In the present work the frequency dependence of the MI is studied for the nanocrystalline Fe73 ,Cu,Nb3SiI3 ,B9 ribbons with high value of stressinduced magnetic anisotropy in correlation with the magnetization process 11 EXPERlMEWCAL TECHNIQUES Amorphous Fe73 sCuINb& sB9 ribbo...

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