78 Acta Electrotechnica et Informatica, Vol. 13, No. 1, 2013, 78–81, DOI: 10.2478/aeei-2013-0017 ISSN 1335-8243 (print) © 2013 FEI TUKE ISSN 1338-3957 (online) www.aei.tuke.sk www.versita.com/aei IMPACT OF PHOSPHORUS FOR BORON SUBSTITUTION ON MAGNETIC PROPERTIES OF MAGNETOSTRICTIVE FINEMETS Beata BUTVINOVÁ * , Pavol BUTVIN * , Emília ILLEKOVÁ * , Peter ŠVEC, Sr * ., Gabriel VLASÁK * , Dušan JANIČKOVIČ * , Magdaléna KADLEČÍKOVÁ ** * Institute of Physics Slovak Academy of Sciences Bratislava, Slovak Republic ** Institute of Electronics and Photonics FEI Slovak University of Technology Bratislava, Slovak Republic Dúbravská cesta 9, 845 11 Bratislava, Slovak Republic, tel. +421 25 941 0560, e-mail: beata.butvinova@savba.sk ABSTRACT Reduction of Si percentage in Fe-Nb-Cu-B-Si alloys known as Finemets results in 1.5 T saturation, surpassing so the standard Si- rich compositions. However the other soft-magnetic properties are worse due mainly to magnetostriction and the consequences of so- called macroscopic heterogeneity. Therefore phosphorus has been added to the detriment of boron to test, whether this could be the way to suppress the undesired properties of Si-poor Finemets. Phosphorus appears to reduce the vulnerability of the ribbon surfaces to environmental influences at non-vacuum annealing and improves parameters like coercivity and magnetic anisotropy. Crystallization kinetics character remains preserved and critical temperatures change only negligibly. Keywords: magnetic properties, nanocrystalline alloys, soft-magnetic materials, surfaces 1. INTRODUCTION Soft- magnetic materials produced by rapid quenching from the melt known as Finemets (basic composition Fe- Nb-Cu-B-Si) are already of interest for a lot of researchers and electrotechnical developers because of their widely used magnetic properties [1]. Magnetic properties of specific compositions greatly profit from thermal treatment resulting in partial crystallization when nanoscale crystalline grains are embedded in the amorphous rest of the alloy. Apart from the “classic” Finemet composition containing 13.5-15.5 at% of Si, new alternatives are sought to obtain higher saturation induction (B s ) without much sacrifice of increasing coercivity and magnetostriction. Whereas the earlier development line exchanged metals and their percentage (Co for Fe), the other way is to try also exchanging metalloids and/or glass-formers. One of the latest achievements of the later way is B s as high as 1.8 - 1.9 T shown by a composition with P addition and reduced Si percentage [2]. So far less attention has been paid to the consequences of so-called macroscopic heterogeneity (MH), which builds up preferentially during the thermal treatment of magnetostrictive Si-poor compositions [3] devoted for nanocrystallization. The MH goes along with mutual stress between surfaces and ribbon interior and shows significant effect on the resulting magnetic anisotropy – characteristic hard-ribbon-axis (HRA) contribution appears [4]. The above-mentioned quest for the improvement of saturation without significant collateral detriments to other properties, MH inclusive, led us to the choice of a Si-poor Finemet with partial substitution of B by P to study how P affects the properties of higher-B s Finemets. Our work on the “parent“ Si-poor material (without P) points to the presence of surface oxides [5] capable of supporting MH and so the question how can phosphorus affect the MH is opened by the P for B substitution too. 2. MATERIALS AND METHODS Planar-flow casting on air was used to prepare the ribbons of 10 mm width and 18 – 26 μm thickness following in the text, labels to identify the composition are used as follows: Fe 78 Nb 3 Cu 1 B 13.5 Si 4.5 - FM(Si4.5), Fe 74 Nb 3 Cu 1 B 13 Si 9 - FM(Si9), Fe 78 Nb 3 Cu 1 P 3 B 10 Si 5 – FM-P(Si5), Fe 74 Nb 3 Cu 1 P 3 B 10 Si 9 – FM-P(Si9). Amorphous ribbons were submitted to differential scanning calorimetry (DSC) in Perkin-Elmer DSC7 under Ar atmosphere to determine the temperature of crystallization onset T x , temperature of first crystallization T p and Curie temperature T C . Thermo-gravimetric analysis (TGA) at applied magnetic field was performed to check more details of T C . The nanocrystalline state and ensuing magnetic properties were obtained by annealing at 500 and 540°C for 1 hour in vacuum and in Ar (without preceding furnace evacuation). We measured the hysteresis loops of 10 cm long strips at 21 Hz sine-H excitation in Helmholtz coils. Raman spectroscopy investigation of strip surfaces used the confocal system with 632.8 nm monochromatic laser radiation. Capacitive sensor measured the magnetostrictive strain to facilitate the determination of coefficients of saturation magnetostriction λ s . 3. RESULTS AND DISCUSSION 3.1. Structure and transformation Very similar transformation process has been observed for P-containing as well as for P-free ribbons by DSC measurement at 10 K/min and 40 K/min rate. As it is seen from Fig. 1, all the curves show the typical regions: structural relaxation, Curie temperature, structural rearrangement at 350-450°C [6] and the first Unauthenticated | 194.138.39.60 Download Date | 1/15/14 2:53 AM