Journal of ELECTRICAL ENGINEERING, VOL. 56, NO. 1-2, 2005, 21–25 PROPERTIES OF M–TYPE BARIUM FERRITE DOPED BY SELECTED IONS Jozef Sl´ ama * — Anna Gruskov´ a ** — M´ aria Pap´ anov´ a ** Darina Kevick´ a ** — Vladim´ ır Janˇ c´ arik * — Rastislav Dosoudil * Guillermo Mendoza-Su´ arez *** — Alvaro Gonz´ alez-Angeles *** The magnetic and structural properties of substituted Ba hexaferrite M-type samples with composition BaFe 12-2x (Me 1 − Me 2 )xO 19 ,where Me 1 = Zn, Co, Ni, and Me 2 = Zr, Ti, were compared. The powder samples with 0.0 ≤ x ≤ 0.6 were prepared by two processing routes. Different Fe/Ba ratio was used for mechanical alloying (Fe/Ba = 10.0) and for the citrate precursor method (Fe/Ba = 10.8 ). Magnetic properties were studied by both vibrating sample magnetometry and thermomagnetic analysis. The ferrite formation process was followed by Mssbauer spectroscopy. Keywords: substituted hexagonal ferrite, organometallic precursor, mechanical alloying, magnetic properties 1 INTRODUCTION M-type barium hexaferrite BaFe 12 O 19 exhibits high- saturated magnetic polarisation J s , strong uniaxial crys- talline anisotropy and large coercivity H c . For this rea- son, it is mainly utilized for the production of permanent magnets. Nevertheless, when substituting Fe 3+ and/or Ba 2+ ions by other metal cations or cation combina- tions, its great magnetocrystalline anisotropy can be di- minished, which leads to its new properties for a variety of applications. Substituted barium hexaferrites are suit- able for high-density perpendicular and magneto- opti- cal recording [1], and microwave devices applications [2]. These electronical applications require a material with strict control of its properties such as magnetic param- eters, homogeneity, particle size and shape, temperature dependence of the coercivity ΔH c /ΔT and remanent po- larization J r . Co-Ti mixture is one of the most studied that has demonstrated that H c decreases (from ∼ 360 kA/m to ∼ 80 kA/m) with the increase in substitution level 0 ≤ x ≤ 0.6 without a significant reduction of magnetic polar- isation [1]. Moreover, narrow switching field distribution (SFD) and excellent high-frequency response were found for this substitution [3, 4]. On the other hand, it is known, that Ni 2+ ions reduce the temperature coefficient of co- ercivity (ΔH c /ΔT ), which is an important parameter for the stability of the recorded data [5]. Likewise, it has been shown that Zn 2+ ions have preference for 4f 1 tetrahedral sites and Ti 4+ ions for 4f 2 and 12k octahedral sites in BaM doped with Zn-Ti, besides, this hexaferrite possesses a positive temperature coefficient of coercivity [6]. Zn-Zr substituted barium hexaferrite nanoparticles exhibit an extraordinary high J s at low substitutions (maximum at x =0.4), and a coercivity easily controllable (from 360 kA/m to 16 kA/m) [4]. Single-phase formation in Co- Zr system with the best properties was observed after calcination in a flux of NaCl at 900 ◦ C for 4 h [7]. How- ever, from economical point of view, Zr- salts are cheaper than those of Ti. In addition, these salts are easily solu- ble in water, being so even more suitable for liquid phase preparation [8]. In this paper, the effect of several metal ion combina- tions (Zn, Co, Ni with Zr or Ti) on the magnetic proper- ties and magnetocrystalline structure of the barium hexa- ferrite was investigated. The samples were synthesized by citrate precursor method and mechanical alloying. The estimation of the influence of doping concentration on structural parameters is shown. 2 EXPERIMENTAL Sample preparation route (1) — The preparation route, where the samples are labelled as (Mx), is as fol- lows: Fe 2 O 3 , BaCO 3 , ZnO, NiO, TiO 2 and ZrO 4 purity ( ∼ 98 %), were used as raw materials. The Fe/Ba ratio of 10 was chosen. Mechanical alloying was performed in a high-energy mill (Segvary Attritor) using a ball/powder ratio of 15. Milling was carried out for 45 h in air with an angular frequency of 400 rpm. A liquid medium (250 ml of benzene) was added to avoid agglomeration of powders at the bottom of the mill, and to assure active participa- tion of powders in the milling process. After mechanical milling, the powders were annealed at 1050 ◦ C for 1.5 h. Sample preparation route (2) - samples labelled as (Sk), with high purity (99 %) Fe(NO 3 ) 3 .9H 2 O, Ba(OH) 2 . 8H 2 O, and other reagents (ie ZrOCl 2 , titanyl acety- lacetonate TiO(acac) 2 , Zn(CH 3 COO) 2 , Co(NO 3 ) 2 or Ni(NO 3 ) 2 ) were used as the starting materials. In this ∗ Slovak University of Technology, Faculty of Electrical Engineering and Information Technology, Department of Electromagnetic Theory, ∗∗ Department of Electrotechnology, Ilkoviˇ cova 3, 812 19 Bratislava 1, Slovakia, E-mail: maria.papanova@stuba.sk ∗∗∗ CINVESTAV-Saltillo-Mty Km. 13, Apdo. P.O.Box 663, 25900 Saltillo, Coah, Mexico, ISSN 1335-3632 c  2005 FEI STU