# Spark Plasma Sintered Manganese Substituted Strontium M-type Nanohexaferrite

Adel Sassi¹,², Alexandre Pasko¹, Venkateswara Yenugonda², Selma Amara³, Camelia Florina Florica⁴, Gianluca Setti³, Frédéric Mazaleyrat¹, Arjun K. Pathak², #

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## Introduction

La-Co substituted hexaferrites are the most performant ferrites in the market of permanent magnets [1]. However, La and Co belong to the family of rare earth and strategic elements and to avoid their usage, nanostructuring ferrites which improve high Hc [2] is being studied as a possible alternative.

Nanopowders of manganese substituted strontium M-type hexagonal ferrites SrMnxFe12-xO19 with x= 1 to 6 were successfully synthesized using the citrate precursor sol-gel method [3,4]. The obtained nanopowders were calcined at 950°C and then were Spark Plasma Sintered at 800°C. XRD analysis at room temperature and magnetometry in a maximum field of 6 T at temperatures ranging from 5 to 375 K were performed on the nanopowders as well as on their sintered pellets.

## Methods and Materials

<figure><img src="image_2.png" /><figcaption>Fig. 1: The different steps of the citrate precursor sol-gel synthesis method of the hexaferrite nanopowders and the sintered pellets.</figcaption></figure>

## Structural analysis

<figure><img src="image_3.png" /><figcaption>Fig. 2: XRD patterns of SPS Mn substituted SrM hexaferrite compared to a monophasic SPS SrM hexaferrite XRD pattern.</figcaption></figure>

## Magnetic properties

<figure><img src="image_4.png" /><figcaption>Fig. 3: M-H loop of Mn substituted SPS SrM hexaferrite pellets measured in the easy and hard axes.</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>Fig. 4: Magnetic properties ($M_r$, $M_s$, $H_c$ and $M_r/M_s$) of Mn substituted SrM hexaferrite as a function of Mn content.</figcaption></figure>

<figure><img src="image_6.png" /><figcaption>Fig. 7: $BH_{max}$ of Mn substituted SrM hexaferrite as a function of Mn content.</figcaption></figure>

## Conclusions

* $M_s$, $M_r$, $H_c$ and $M_r/M_s$ decrease by increasing the Mn content

* SPS presumably partially decomposes M ferrite into spinel (reduction of Mn3+)

* Coercivity increases reaching as high as 0.76 T in the sintered (SrMn₆Fe₆O₁₉) pellet.

* Coercivity drastically decreases after sintering reaching 67% of the coercivity of the starting loose powder for x = 6

## Acknowledgments

The PPMS magnetic measurements were performed at the State University of New York (SUNY), Buffalo State University, and supported by the U.S. National Science Foundation Award No. DMR-2213412.

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January 13-17, 2025 • New Orleans, Louisiana

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## References

1. F. Kools, A. Morel, R. Grössinger, J. M. Le Breton, P. Tenaud, J. Magn. Magn. Mat.242-245 (2002) p. 1270-1276

2. Mazaleyrat, F., Pasko, A., Bartok, A., & LoBue, M. . Giant coercivity of dense nanostructured spark plasma sintered barium hexaferrite. Journal of Applied Physics 109 (2011) 07A708.

3. Tayssir Ben Ghzaiel, Wadia Dhaoui, Alexandre Pasko, Frédéric Mazaleyrat, Effect of non-magnetic and magnetic trivalent ion substitutions on BaM-ferrite properties synthesized by hydrothermal method, Journal of Alloys and Compounds 671 (2016) pp. 245-253,

4. A. K. Pathak and A. Sassi, Magnet powder and sintered magnet of strontium and barium M-type modified hexagonal ferrite, Pat. Ref. 160-2251P0, US Pat. No.: 63/600,105