In situ crystallization and magnetic measurement of hexaferrite glass-ceramics

Arumala J Lere-Adams,Mostafa Ahmadzadeh,John S Mccloy,Scott Boroughs,Natalie Smith-Gray,David Bollinger

doi:10.1063/9.0000063

Arumala J Lere-Adams, Mostafa Ahmadzadeh + Show 4 more

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https://doi.org/10.1063/9.0000063

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Journal: AIP Advances	Publication Date: Mar 1, 2021
Citations: 1	License type: cc-by

Affiliation: Washington State University

Abstract

Glass-ceramic (GC) materials have the formability advantages of glasses and the opportunity for controlled crystallization of functional ceramic phases. Here, we obtain GCs containing the hard magnetic phase Sr-hexaferrite (SrFe12O19) from a borate glass. Ten compositions in the B2O3-Fe2O3-SrO system were explored, varying B2O3 and Sr/Fe ratio. Compositions forming glass on quenching, according to X-ray diffraction (XRD), were subsequently heat treated to promote crystallization. Three selected compositions were investigated with vibrating sample magnetometry (VSM), thermal analysis, and electron probe microanalysis (EPMA). Phases identified by XRD after air heat treatment included α-Fe2O3, Fe3O4, SrB2O4, and SrFe12O19. Glasses were also crystallized in situ in a VSM in an argon environment, measuring magnetic properties during heating to 650°C after in situ heat treatment at 800°C. In samples with SrFe12O19, wasp-waisted loops were observed. First order reversal curve (FORC) measurements confirmed low (magnetite) and high (Sr-hexaferrite) coercivity phases. Room temperature VSM measurements of argon in situ treated samples were compared with two ex situ air heat treated protocols. The microstructures of the three investigated air heat treated GC materials were completely different, and compositional position on the phase diagram appeared to influence crystallization progress. These results suggest that careful control of composition as well as heat treatment protocol including atmosphere is necessary for crystallization of desired magnetic phases. Also, VSM was confirmed to be sensitive to magnetic phases at low concentrations not visible to XRD.

Highlights

The M-type hexaferrites, MO⋅6Fe2O3 or MFe12O19 (M = Ba, Sr, or Pb) are important ferromagnetic oxides that have traditionally been used as permanent magnets in applications for dielectric media because of their high values of magneto-crystalline anisotropy and saturation magnetization.[1,2] Using the compositional and manufacturing flexibility of glasses, and allowing for crystallization of functional ceramic phases, magnetic glass-ceramics with hard phases like hexaferrites can be obtained.[3]
Most current research in magnetic glass ceramics focuses on spinel ferrite (LiFe5O8), magnetite, or hematite as the active magnetic phases in silicate glass,[5,6] though borate glasses have been proposed as sintering aids for bulk Sr hexaferrite magnets.[7]
By varying B2O3 concentration of the glass system and Sr/Fe ratio we found that the most suitable compositions for hexaferrite had B/Sr molar ratio ≤ 2 and SrO ≥ 43 mol%

Summary

Introduction

Magnetic GCs are currently of interest in cancer research due to the favorable combination of biocompatibility and the potential for non-invasive hyperthermia therapy.[4] Potentially advantageous over nanoparticles, GCs retain crystallized magnetic phases while encapsulating them to help avoid oxidation. Most current research in magnetic glass ceramics focuses on spinel ferrite (LiFe5O8), magnetite, or hematite as the active magnetic phases in silicate glass,[5,6] though borate glasses have been proposed as sintering aids for bulk Sr hexaferrite magnets.[7]

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