Growth of (Ni,Zn)Fe 2 O 4 Thin Films by Liquid Delivery Metal-Organic Chemical Vapor Deposition
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ABSTRACT Ni,Zn-ferrite (NZF) thin films are of interest for high frequency applications because of their high saturation magnetization compared to garnet films and their low eddy current losses compared to metal alloy films. Therefore there is an increasing need for methods to deposit single crystal ferrite thin films for incorporation into next generation microwave devices. Epitaxial thin films of NZF have been deposited by liquid delivery metal-organic chemical vapor deposition onto (100) oriented MgO substrates. The morphology, orientation and magnetic properties of the as-deposited films were investigated as a function of deposition temperature and pressure. X-ray diffraction (XRD) reveals highly oriented films with a film strain of 1.01% compared to bulk lattice parameters. Films with well saturated magnetic hysteresis were obtained under a number of conditions with values of saturation magnetization up to 270 emu/cc (3400 gauss) with relatively low coercive fields -100 Oe. The influence of metal cation ratio on magnetic properties is discussed.
INTRODUCTION Ferrite thin films are of interest for their potential use in high frequency devices. Compared to other bulk ferrites, NZF exhibits the most desirable magnetic properties for high frequency devices, including large magnetization and low coercive field. Several techniques have been used to synthesize NZF to date. These include pulsed laser deposition (PLD) 3 , spin-spray ferrite plating4 , rf plasma deposition 5, as well as standard ceramic routes 6. While techniques such as PLD are promising because they may yield stoichiometric NZF, issues such as step coverage and uniformity across large areas are difficult to overcome. Chemical vapor deposition yields quality films with good step coverage together with the ability to control film growth. It is therefore necessary to develop reproducible, scalable MOCVD processes for hybrid microwave devices. We 7 have previously reported the use of this technique to produce NiFe 20 4. In this paper we have extended the previous work to include Zn substitution. Xray diffraction and double crystal rocking curve analysis (DCRC) were used to investigate the structure and orientation of these films. Field emission scanning electron microscopy (FESEM) was used to investigate the surface microstructural and morphological characteristics of our films. Magnetic properties were determined by use of a vibrating sample magnetometer (VSM.) Finally, film composition was investigated via Rutherford backscattering spectroscopy (RBS) and wavelength dispersive x-ray fluorescence (WDXRF.) Relationships between A/B cation ratios and magnetic properties are discussed as well as comparisons of film properties with bulk values.
169 Mat. Res. Soc. Symp. Proc. Vol. 574 ©1999 Materials Research Society
Saturation magnetization and coercive field values for various bulk NZF compositions are summarized in Table 1. Table 1: Bulk values of saturation magnetization and coercive field as a function *8 of NiFe 2O4 :ZnFe 2O4 molar ratio. NiFe2O
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