Hard meets soft: tuning binary ferrofluids

Abstract

We study binary ferrofluids composed of multicore "nanoflowers" of magnetically hard CoFe2O4 and magnetically soft MnFe2O4, as a way to optimise heat dissipation while suppressing aggregation-properties essential for biomedical applications. Bulk magnetometry and molecular dynamics simulations were combined to elucidate their behaviour. Experiments show wasp-waisted hysteresis, composition-dependent coercivity, and strong protocol dependence (field cooling). Simulations reproduce these trends and reveal the underlying structure-property coupling: (i) in an applied magnetic field, CoFe2O4 forms chains that dominate collective switching; (ii) adding MnFe2O4 "poisons" these chains-shortening and de-branching clusters-thereby lowering coercivity and loop area relative to a weighted superposition of the individual component responses without interactions; (iii) dipolar coupling reciprocally hardens the magnetically soft phase and softens the magnetically hard phase even without large-scale aggregation; and (iv) at higher total volume fraction (ϕ = 0.1) magnetically soft particles still suppress chain growth, reducing mean cluster size by up to an order of magnitude while keeping heating-relevant hysteresis close to Stoner-Wohlfarth expectations. These results establish composition-controlled microstructure as a means to decouple thermal output from aggregation: CoFe2O4 : MnFe2O4 mixtures can be tuned to enhance loss mechanisms while mitigating aggregation, offering a route to binary ferrofluids optimized for magnetic hyperthermia and drug delivery.

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BibTeX RIS

BibTeX

@article{khelfallah2026hard,
  title = {{Hard meets soft: tuning binary ferrofluids}},
  author = {Malika Khelfallah and Ekaterina V Novak and Andrey A Kuznetsov and Deniz Mostarac and Niéli Daffé and Marcin Sikora and Sophie Neveu and Jovana Zečević and Johannes D Meeldijk and Dario Taverna and Philippe Sainctavit and Mauro Rovezzi and Hebatalla Elnaggar and Enzo Bertuit and Nicolas Mille and Rachid Belkhou and Vincent Dupuis and Claire Carvallo and Amélie Juhin and Sofia S Kantorovich},
  journal = {Nanoscale},
  year = {2026},
  month = nov,
  doi = {10.1039/d5nr05218a},
  url = {https://hal.sorbonne-universite.fr/hal-05850566v1},
  note = {CC BY 4.0},
}

RIS

TY  - JOUR
TI  - Hard meets soft: tuning binary ferrofluids
AU  - Malika Khelfallah
AU  - Ekaterina V Novak
AU  - Andrey A Kuznetsov
AU  - Deniz Mostarac
AU  - Niéli Daffé
AU  - Marcin Sikora
AU  - Sophie Neveu
AU  - Jovana Zečević
AU  - Johannes D Meeldijk
AU  - Dario Taverna
AU  - Philippe Sainctavit
AU  - Mauro Rovezzi
AU  - Hebatalla Elnaggar
AU  - Enzo Bertuit
AU  - Nicolas Mille
AU  - Rachid Belkhou
AU  - Vincent Dupuis
AU  - Claire Carvallo
AU  - Amélie Juhin
AU  - Sofia S Kantorovich
PY  - 2026
DA  - 2026/11/03
JO  - Nanoscale
DO  - 10.1039/d5nr05218a
UR  - https://hal.sorbonne-universite.fr/hal-05850566v1
AB  - We study binary ferrofluids composed of multicore "nanoflowers" of magnetically hard CoFe2O4 and magnetically soft MnFe2O4, as a way to optimise heat dissipation while suppressing aggregation-properties essential for biomedical applications. Bulk magnetometry and molecular dynamics simulations were combined to elucidate their behaviour. Experiments show wasp-waisted hysteresis, composition-dependent coercivity, and strong protocol dependence (field cooling). Simulations reproduce these trends and reveal the underlying structure-property coupling: (i) in an applied magnetic field, CoFe2O4 forms chains that dominate collective switching; (ii) adding MnFe2O4 "poisons" these chains-shortening and de-branching clusters-thereby lowering coercivity and loop area relative to a weighted superposition of the individual component responses without interactions; (iii) dipolar coupling reciprocally hardens the magnetically soft phase and softens the magnetically hard phase even without large-scale aggregation; and (iv) at higher total volume fraction (ϕ = 0.1) magnetically soft particles still suppress chain growth, reducing mean cluster size by up to an order of magnitude while keeping heating-relevant hysteresis close to Stoner-Wohlfarth expectations. These results establish composition-controlled microstructure as a means to decouple thermal output from aggregation: CoFe2O4 : MnFe2O4 mixtures can be tuned to enhance loss mechanisms while mitigating aggregation, offering a route to binary ferrofluids optimized for magnetic hyperthermia and drug delivery.
SN  - 2040-3364
SN  - 2040-3372
ER  -

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