M-type barium hexaferrite synthesis and characterization for phase shifter applications

Abstract

M-type barium hexaferrite films have been grown by liquid phase epitaxy and examined by x-ray diffraction, scanning electron microscopy, atomic force microscopy, and conventional and Lorentz-mode transmission electron microscopy (TEM). These films exhibit a diamond chevron shaped "brick wall" microstructure with c-axis oriented hexaferrite platelets. The films are oriented with their c axes in-plane, and parallel to the M-plane sapphire substrate, and exhibit a 30 rotation about the c axis with respect to the substrate. Rocking curves showed (20À20) and (22À40) FWHM values of 1.09 and 1.56 , respectively, for the thinner of two samples, and 0.31 and 0.50 for the thicker sample. The magnetic domain structures have been characterized by Lorentz-mode TEM and the domain walls were found to be pinned to small angle tilt boundaries. Using the measured rocking curve values, the effect of the overall crystalline misorientation on the dispersion of the magnetocrystalline anisotropy of the samples is estimated to be less than half a percent. Since M-type barium hexaferrite was originally examined in the late 1930s by Adelskold, 1 and further studied by Gorter and Braun at Philips in the 1950s, 2,3 the unique properties associated with its anisotropic magnetic and crystalline structures have made the system of great interest to both scientists and engineers. [4][5][6] These properties include high permeability, electrical resisitivity, and high ferromagnetic resonance (FMR) frequencies, with relatively narrow FMR linewidths. Additionally, the ability to grow hexaferrite films with the crystallographic c axis aligned either in plane or perpendicular to the plane provide these materials with magnetic anisotropy that make them suitable for various applications. Phase shifters, delay lines, filters, and antenna applications can be fabricated from films with in-plane anisotropy, and isolator and circulator applications can be fabricated from films possessing perpendicular magnetic anisotropy. 7 While these properties are important in determining hexaferrites' utility as microwave materials, they also have excellent radiation resistance and high power handling capacities that make them ideal for next-generation microwave devices, especially for use in extreme environments. 8,9 The structure of the hexaferrites is unique in that all the observed structures, including M type, Y type, Z type and so on, are made up of common subunits that are present in different numbers and repeat sequences. 4,10 All subunits are built upon a close packed lattice of oxygen with different metal ion arrangements. For example, in the case of M-type barium hexaferrite, the stacking sequence is RSR*S* in which R represents a rhombohedral subunit and S represents a spinel subunit. The asterisk (*) represents a 180 rotation of the subunit about the c axis.In growing epitaxial films, the lattice mismatch between the substrate and the film causes crystalline domains to form. 11 This generally has deleterious effects on the properties of the film for use at ...

Orientation Growth and Magnetic Properties of BaM Hexaferrite Films Deposited by Direct Current Magnetron Sputtering

“…However, preparation of in-plane c-axis highly aligned BaM films has always been a challenge, and the influence of various processing parameters remains unclear. Although high-quality inplane c-axis oriented BaM films have been successfully prepared using pulsed laser deposition (PLD) 12,[14][15][16] and liquid phase epitaxy (LPE) 11,[17][18][19] techniques, these methods, however, require expensive equipment. In our previous study, inplane c-axis oriented BaM films were fabricated using DC magnetron sputtering, a proven cost-effective method suitable for industrial production, which has a higher deposition rate than radio-frequency (RF) magnetron sputtering.…”

Single crystal growth from the melt and magnetic properties of hexaferrites–aluminates

“…There are different devices of resonance type (filters, phase circulators, etc.) and multiferroic structures [1][2][3][4][5][6][7][8][9]. The most popular hexaferrites, pure Ba and Sr, have magnetic anisotropy fields of 17 and 19 kOe, respectively.…”

Magnetic Properties and Hyperfine Interactions in M-Type BaFe12-2xMoxZnxO19 Hexaferrites

“…The magnetic properties, in addition to corrosion re-sistance and low production cost, make these ferrites of great commercial and technological importance [1,2]. The great current scientific and technological interest in M-type ferrites was driven by their potential for a wide range of applications in permanent magnets, high density magnetic recording and data storage media, microwave absorption and next-generation microwave devices [1][2][3][4][5][6][7][8].…”