Remanence Properties Of Barium Hexaferrite, Volume 369

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Journal of Alloys and Compounds 369 (2004) 185–189 Remanence properties of barium hexaferrite P.E Garcia-Casillas a,d,∗ , A.M Beesley b , D Bueno c , J.A Matutes-Aquino c , C.A Martinez d a Depto de Inv Grupo Cementos de Chihuahua S.A de C.V., Chihuahua, Chih., Mexico Department of Physics, University of Liverpool, Oxford Street, Liverpool L69 7ZE, UK c Centro de Investigacion en Materiales Avanzados, Miguel de Cervantes 120, Complejo Industrial Chihuahua, C.P 31109, Chihuahua, Chih., Mexico d Instituto de Ingenier´ıa y Tecnolog´ıa Universidad Autónoma de Ciudad Juárez, Ave del Charro # 610 Norte, Cd Juárez, Chihuahua, Chih., Mexico b Abstract Barium hexaferrites have been widely used as permanent magnets, however one of the most important parameters that characterizes these ferrites is the switching field distribution (SFD) This work calculates the SFD on a small particle barium ferrite (BaFe12 O19 ) obtained by coprecipitation from chlorides in an alkaline medium using the irreversible component of the magnetization Forward and reverse switching field distribution curves were obtained by differentiation of isothermal remanent magnetization (IRM) and dc demagnetisation (DCD) curves It was found that both values differ by a factor of 3.5, quite away from the value of non-interacting systems The Henkel plot was built from these data sets, indicating a predominant region with demagnetising interaction between particles, and a small region in which the particles interact constructively to the magnetization, according to the Preisach model framework © 2003 Elsevier B.V All rights reserved Keywords: Chemical synthesis; Scanning and transmission electron microscopy; Magnetic measurements Introduction Barium ferrite (BaFe12 O19 ) has been commonly used as permanent magnet since its development in the beginning of the 1950s by Phillips researches In fact, this material presents high saturation magnetization, high Curie temperature, high intrinsic coercivity and rather large crystal magnetic field anisotropy [1,2] Due to these properties, many methods of synthesis have been developed to obtain a low production cost of fine particles of barium ferrite with a good chemical homogeneity, in this sense coprecipitation seems to be the most suitable at the moment [2–5] However it is of great importance the level of stacking of Ba ferrite particles which is believed to determine the magnetic interparticle interactions, affecting essential properties such as thermal duplication, media noise and resolution in longitudinal recording media [1,6] The deviation from the Stoner–Wohlfarth model is a technique to estimate interparticle interactions but it is restricted to uniaxial single domain particles Barium ferrite obtained by coprecipitation consists of hexagonal plates and can be considered as a uniaxial system, however the size of these particles determines whether ∗ Corresponding author Tel.: +52-614-442-3100; fax: +52-614-442-3288/3275 E-mail address: (P.E Garcia-Casillas) 0925-8388/$ – see front matter © 2003 Elsevier B.V All rights reserved doi:10.1016/j.jallcom.2003.09.100 or not they are single- or multi-domains Therefore a more general theory is needed to describe these interactions The Preisach hysteresis model provides the framework to make the Wohlfarth relation valid for multi-domain systems This model considers the magnetic material as a distribution of small hysteresis loops or “hysterons”, which are determined by (hc , hu ) units in which hc represents its coercive field and hu is the displacement of the hysteron from origin (0, 0) in the magnetization versus field plane [7] These hysterons can be considered as Stoner–Wohlfarth particles only if they represent the reversible component of the magnetization The values hc and hu of each hysteron determine the Preisach plane (hc versus hu ) The three remanent states, magnetising (Mr ), demagnetising (Md ) and saturation (M∞ ) are associated with three partitions of the Preisach plane [7,8] Considering that the Preisach distribution is concentrated along the hc -axis (hu = 0), the upper limit of the Henkel plot region is determined by the relation Md = M∞ − 2Mr , as the Wohlfarth model In that case if Md ≥ (97% of the theoretical density Only M-type Ba-ferrite and Ba-borate is detected by X-ray di€raction The magnetic properties of the compact glass ceramics are comparable with those of the annealed ¯akes The speci®c saturation magnetization of such samples lies between 26 and 28 Am2 kgÀ1, i.e 90±100% of the possible value corresponding to the ferrite content of 40% and assuming a bulk material value of 72 Am2 kgÀ1.3 The coercivities reach values above 400 kA mÀ1 2.3 Glass ceramics with SiO2 matrix For applications a glass ceramic with a ferrite content as high as possible is desirable In order to increase the ferrite content of the annealed ¯akes above 50%, a high Fe2O3-content of the initial melt (>35 mol%) is necessary but leads to large ferrite crystals which show the full magnetization values but lower coercivities ([...]... Kojima [8] In an earlier work, nanosize barium hexaferrite was prepared following hydrothermal precipitation –calcination technique [9] Since there is no literature available on the effect of Al substitution on the structural properties of barium hexaferrite, the present work has been taken up to study the effect of aluminum substitution on the phase formations of barium ferrite following a hydrothermal... magnetic properties of substituted BaM directly depend on the electronic configuration of the substituting cations and on their preference to occupy the different Fe sublattices of the hexagonal structure It has also been highlighted that the magnetic properties of BaM are related to the occupancy of the Fe3 + ions at the different sublattices of the magnetoplumbite structure [7] The influence of the... ratio, formation of different compounds take place during calcination at temperatures in the range of 800 –1200 jC The decomposition of BaCO3 will give BaO and CO2 and de-hydroxylation of AlOOH will give Al2O3 These oxides would stay as such or form aluminum-substituted barium hexaferrite as discussed in the previous sections 3.3 Comparison of Al-substituted barium ferrites with pure barium hexaferrite... size compared with the original barium ferrite particles While the sample (a) is composed of much larger grains with a wide grain size distribution of 2 Á/7 mm Large pores were also formed due to the irregular alignment of larger hexagonal platelets Fig 3 shows the effect of particles fabrication temperature on high-frequency magnetic properties of Co Ã/Ti substituted barium ferrites sintered at 900... Magnetic properties vs NiSn-substitution hysteresis loop and the magnetic properties The slope of the initial magnetization curve gives one idea of the behavior of the magnetic susceptibility It can be seen that w increased with the Ni–Sn substitution This observation is in agreement with the temperature dependence of the magnetic susceptibility, wðyÞ measurements (Fig 5) The behavior of the magnetic properties. .. the magnetic properties of pure BaM has been investigated by Surig et al [8] They found that a Fe/Ba value of 10.5 yielded the best Fig 2 Saturation magnetisation and coercivity of BaFen À 2xZnx TixO19 samples heat-treated from 900 to 1000 jC for 4 h (10 V n V 11.6) magnetic properties due to the absence of intermediate phases This paper reports on the room temperature magnetic properties of Zn – Ti-substituted... composed of small grains with little porosity, indicating little change of particle size compared with the original barium ferrite particles Whereas the sample (b) that sintered with 2 wt% Bi2O3 doping is composed of much larger grains with a grain size distribution of 1–6 mm The more and larger pores were formed due to the irregular alignment of larger hexagonal platelets Effects of temperatures for barium. .. substitution of the Ba2 + and/or the Fe3 + ions with mixtures of paramagnetic and diamagnetic ions in the magnetoplumbite structure is to reduce the high magnetocrystalline anisotropy of the material [1] Besides the prime importance of the anisotropy field, also significant are the decrease of the crystallite size below 100 nm, the increase of the aspect ratio (diameter/thickness), and the enhancement of the... substitution of Al into the barium hexaferrite can be done only up to Fe/Al as 5 However, the substituted hexaferrite also had hematite as the crystalline phase Due to the stability of BaCO3 with higher aluminum content in the presence of iron, formation of aluminum-substituted barium ferrite is hindered 3.4 VSM measurements The XRD patterns for the BaFe12O19 and its iso-phasic Al-substituted barium ferrite... Regarding Mr ; this registered a fall of B20%, as x increased, presumably, owing to the increase of the volume fraction of NiFe2O4 in the structure On the other hand, Ms remained practically constant Our results suggest that the effects of Ni–Sn substitutions on the magnetic properties are similar to those produced by Ir–Co and Ir–Zn mixtures However, from the economical point of view, Ni and Sn-bearing oxides
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