Superparamagnetic blocking and superspin-glass freezing in ultra small δ-(Fe0.67Mn0.33)OOH particles
文献信息
G. Ennas, A. Scano, E. Agostinelli, D. Fiorani
The magnetic properties of ultra-small (∼2 nm) δ-(Fe0.67Mn0.33)OOH nanoparticles prepared by a microemulsion technique have been investigated by magnetization and ac susceptibility measurements at variable frequency. The results provide evidence of two different magnetic regimes whose onset is identified by two maxima in the zero-field-cooled susceptibility: a large one, centered at ∼150 K (Tmh), and a narrow one at ∼30 K (Tml). The two temperatures exhibit a different frequency dependence: Tmh follows a Vogel–Fulcher law τ = τ0 exp[(Ea/kB)/(T − T0)], indicating a blocking of weakly interacting nanoparticle moments, whereas Tml follows a power law τ = τ0(Tg/Tmν − Tg)α, suggesting a collective freezing of nanoparticle moments (superspin-glass state). This picture is coherent with the field dependence of Tml and Tmh and with the temperature dependence of the coercivity, strongly increasing below 30 K.
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Physical Chemistry Chemical Physics

Physical Chemistry Chemical Physics (PCCP) is an international journal co-owned by 19 physical chemistry and physics societies from around the world. This journal publishes original, cutting-edge research in physical chemistry, chemical physics and biophysical chemistry. To be suitable for publication in PCCP, articles must include significant innovation and/or insight into physical chemistry; this is the most important criterion that reviewers and Editors will judge against when evaluating submissions. The journal has a broad scope and welcomes contributions spanning experiment, theory, computation and data science. Topical coverage includes spectroscopy, dynamics, kinetics, statistical mechanics, thermodynamics, electrochemistry, catalysis, surface science, quantum mechanics, quantum computing and machine learning. Interdisciplinary research areas such as polymers and soft matter, materials, nanoscience, energy, surfaces/interfaces, and biophysical chemistry are welcomed if they demonstrate significant innovation and/or insight into physical chemistry. Joined experimental/theoretical studies are particularly appreciated when complementary and based on up-to-date approaches.














