Approach to Ferromagnetic Saturation for the Bulk Amorphous Alloy

Vol. 127 (2015) ACTA PHYSICA POLONICA A No. 2

Proceedings of the European Conference Physics of Magnetism, Pozna« 2014 Approach to Ferromagnetic Saturation for the Bulk Amorphous Alloy:

(Fe0.61Co0.10Zr0.025Hf0.025Ti0.02W0.02B0.20)97Y3 K. Bªoch* and M. Nabiaªek Cz¦stochowa University of Technology, Faculty of Materials Processing Technology and Applied Physics, Cz¦stochowa, Poland The aim of this paper was to conduct studies concerning the magnetization of bulk amorphous

(Fe0.61Co0.10Zr0.025Hf0.025Ti0.02W0.02B0.20)97Y3 alloy when subjected to strong magnetic elds: the specic fo- cus of the paper is the area known as the approach to ferromagnetic saturation. The investigated alloy samples were produced using the suction-casting method, resulting in plates of dimensions 10 mm × 5 mm × 0.5 mm and rods of length 20 mm and diameter 1 mm. The structure was studied using X-ray diractometry. It was found that investigated samples were amorphous in the as-cast state. The magnetization was measured in a strong magnetic eld using a vibrating sample magnetometer. On the basis of the obtained results, the type of structural defects having inuence on magnetization in high magnetic elds were determined for the bulk metallic glasses manufactured with dierent cooling rates. DOI: 10.12693/APhysPolA.127.413 PACS: 75.50.y, 75.50.Kj, 75.30.Ds, 75.20.En, 75.47.Np, 75.50.Bb, 75.60.Ej

1. Introduction can be described by the empirical law of the approach to saturation [6]: The bulk amorphous alloys are also called volumetric 4 ! X n/2 1/2 multicomponent materials. These alloys are character- µ0M(H)=µ0Ms 1− an/2/µ0H +b (µ0H) , ized by a strong proclivity towards forming an amorphous n=1 state, which is achieved by selection of the appropriate where M spontaneous magnetization, µ magnetic chemical composition. The alloy should contain a mini- s 0 permeability of a vacuum, H magnetic eld, a , a , mum of three components; the atomic radii of the main 1/2 1 a gradient coecients of the linear t related with components should dier by about 12%, and moreover, 2 the type of defect, b gradient coecient of the linear the alloy should be characterized by a large negative heat t related to thermal dumping of the spin-waves by the of mixing. It is known that in amorphous alloys there is strong magnetic eld. no long-range ordering of atoms. However, there may This template can be used for estimation of the length be long-range order of the spin magnetic moments in of the published manuscript. amorphous alloys. The magnetic properties of transition metal alloys explicitly depend on the chemical composi- 2. Experimental procedure tion thereof [13]. When the sample alloy is subjected to strong mag- The materials used in the investigations were made netic elds, and the domain structure does not exist any- using the suction-casting method. The structure of the more, a magnetization distribution related to short-range samples was studied by X-ray diractometry. The mag- stresses is present. The sources of these stresses can be netization under the inuence of strong magnetic elds point defects or quasi-dislocational dipoles [4, 5]. One of was measured using a magnetometer with vibrating sam- the indirect methods for investigating the microstructure ple. The investigations of the structure and magnetic of ferromagnetic materials is the law of approach to ferro- properties were performed on samples which had been magnetic saturation in magnetization curves. These mea- powdered in a low energy process. surements provide information about the defect structure. As the point of ferromagnetic saturation is ap- 3. Results and discussion proached, there is rotation of the magnetic moments in the vicinity of these defects. Thermally excited spin The X-ray diraction (XRD) curves for the investi- waves also have an impact on the process of magnetiza- gated alloy are presented in Fig. 1; they display only tion in strong magnetic elds. High-eld magnetization one broad maximum, as is characteristic of amorphous materials. Figure 2 shows high-eld magnetization curves, as a function of the magnetizing eld, for the investigated al- *corresponding author; e-mail: [email protected] loy. In Fig. 2a, the dependence of the reduced magnetization (M/Ms) on the magnetic eld induction is shown

(413) 414 K. Bªoch, M. Nabiaªek

TABLE

Experimental values of the a1/2, b parameters and the spin wave stiness parameter Dsp. Parameter a1/2 b Dsp Form [T 1/2] [T 1/2] [10−2 eV nm2] of samples plate 0.0684 0.0365 60.40 rod 0.0256 0.0451 52.45

Fig. 1. X-ray diraction patterns for as-quenched 4. Conclusions (Fe0.61Co0.10Zr0.025Hf0.025Ti0.02W0.02B0.20)97Y3 powder. The suction-casting method facilitates the production of amorphous alloy samples in the forms of rods and plates. The Kronmüller approach to the ferromagnetic saturation theorem allows for indirect investigations into the structure of the amorphous materials. The results of the investigations in this paper showed that the magnetization process of the alloy is inuenced only by point defects and thermally-induced spin waves. This could be explained by the insignicantly small inuence of the magnetic anisotropy induced during the production process [8]. The HolsteinPrimako paraprocess for the rod- shaped sample occurs over a much wider range than for the plate-shaped sample. According to [9], in the amorphous materials the mean value of the exchange integral varies over a wide range, and areas exist which feature low values of exchange energy. In these areas, the induction of spin waves of low energy is preferred. This

leads to an eective reduction in the Dsp value in com- Fig. 2. The high-eld magnetization curves parison to homogeneous materials with the same value of −1/2 1/2 M/Ms((1/µ0H) ) (a,c) and Ms((µ0H)) (b,d) exchange integral. Therefore for the rod-shaped sample a for the bulk amorphous alloy samples of lower value of the spin wave stiness parameter has been Fe0.61Co0.10Zr0.025Hf0.025Ti0.02W0.02B0.20)97Y3. observed. for the plate-shaped samples of the alloy. In the magnetic References eld induction range of 0.1 T to 0.6 T a linear dependence of the reduced magnetization on −1/2 has been ob- [1] K. Sobczyk, J. Zbroszczyk, M. Nabiaªek, J. Ol- µ0H szewski, P. Br¡giel, J. wierczek, W. Ciurzy«ska, A. served (Fig. 2c). This means that, within this magnetic ukiewska, M. Lubas, M. Szota, Arch. Metal. Mater. eld range, the magnetization process is connected with 53, 855 (2008). small rotations of the magnetic moments in the vicinity [2] A. Inoue, A. Makino, T. Mizushima, J. Magn. Magn. of point defects. Mater. 215, 246 (2000). In stronger magnetic elds, of more than 0.6 T, a linear [3] J. Gondro, J. wierczek, J. Olszewski, J. Zbroszczyk, 1/2 dependence of Ms on µ0H has been observed (Fig. 2d). K. Sobczyk, W.H. Ciurzynska, J. Rz¡cki, M. Nabi- This means that the magnetization process is connected aªek, J. Magn. Magn. Mater. 324, 1360 (2012). with dumping of the thermally-induced spin waves, and [4] H. Kronmüller, J. Ulner, J. Magn. Magn. Mater. 6, hence is denoted HolsteinPrimako [7]. Similar shapes 52 (1977). −1/2 of dependence of the reduced magnetization on µ0H [5] M.G. Nabialek, P. Pietrusiewicz, M.J. Dospial, 1/2 and magnetization on µ0H have been observed for the M. Szota, K. Bªoch, K. Gruszka, K. O¹ga, S. Garus, rod-shaped sample, which, as in the case of the plate- J. Alloys Comp. 615, S51 (2014). shaped sample, is connected to the rotations of the mag- [6] H. Kronmüller, J. Appl. Phys. 52, 1859 (1981). netization vectors in the vicinity of the point defects [7] T. Holstein, H. Primako, Phys. Rev. 58, 1098 −1/2 (Ms proportional to µ0H ) and with the dumping (1940). of the thermally-induced spin waves by the magnetic [8] N. Lenge, H. Kronmüller, Phys. Status Solidi A 95, eld (the HolsteinPrimako paraprocess) (Fig. 2a,b). 621 (1986). The data obtained from the analysis of the high-eld magnetization curves are presented in Table.