Evidence of Individual Superspin Relaxation in Diluted Fe3O4/Hexane Ferrofluids

dc.contributor.authorBotez, Cristian E.
dc.contributor.authorMusslewhite, Zachary
dc.date.accessioned2023-07-13T14:07:24Z
dc.date.available2023-07-13T14:07:24Z
dc.date.issued2023-07-06
dc.date.updated2023-07-13T14:07:25Z
dc.description.abstractWe used dc magnetization and ac susceptibility to investigate the magnetic relaxation of ferrofluids made of 8 nm average-diameter Fe3O4 nanoparticles dispersed in hexane. Samples of different concentrations (δ) spanning two orders of magnitude ranging from 0.66 to 0.005 mg (Fe3O4)/mL (hexane) were used to vary the interparticle interaction strength. Our data reveal a critical concentration, δc = 0.02 mg/mL, below which the ferrofluid behaves like an ideal nanoparticle ensemble where the superspins relax individually according to a Néel–Brown activation law τ(T) = τ0exp (EB/kBT) with a characteristic time τo ~10^(−9) s. That is further confirmed by the observed invariance of the relative peak temperature variation per frequency decade ∆ = ∆T / [T·∆log(f)], which stays constant at ~0.185 when δ < δc. At higher concentrations, between 0.02 and 0.66 mg/mL, we found that ∆ exhibits a monotonic increase with the inverse concentration, 1/δ, and the collective superspin dynamics is described by a Vogel–Fulcher law, τ(T) = τ0exp(EB/[kB(T−T0)]). Within this regime, the dipolar interaction strength parameter T0 increases from T0 = 0 K at δc = 0.02 mg/mL to T0 = 14.7 K at δ = 0.66 mg/mL.
dc.description.departmentPhysics and Astronomy
dc.identifierdoi: 10.3390/ma16134850
dc.identifier.citationMaterials 16 (13): 4850 (2023)
dc.identifier.urihttps://hdl.handle.net/20.500.12588/1977
dc.rightsAttribution 4.0 United States
dc.rights.urihttps://creativecommons.org/licenses/by/4.0/
dc.subjectmagnetic nanoparticles
dc.subjectsuperspin relaxation
dc.subjectac susceptibility
dc.subjectmagnetic nanoparticles
dc.subjectsuperspin relaxation
dc.subjectac susceptibility
dc.titleEvidence of Individual Superspin Relaxation in Diluted Fe3O4/Hexane Ferrofluids
dc.typeArticle

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