Aggregation vs Surface Segregation: Antagonism over the Magnetic Behavior of NiCr Nanoparticles

Murtaza Bohra*, Vidya Alman, Arun Showry, Vidyadhar Singh, Rosa E. Diaz, Mukhles Sowwan, Panagiotis Grammatikopoulos*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

8 Scopus citations


Annealing is a valuable method for fine-tuning the ultrasmall magnetic properties of alloy nanoparticles (NPs) by controlling their sizes, modifying their surfaces, and affecting their magnetic interactions. Herein, we study the effect of moderate annealing (450 °C) on strongly interacting NiCr nanoparticle assemblies (0 ≤ atom % Cr ≤ 15) immediately after deposition. Concurrent temperature-dependent electron microscopy and magnetization data demonstrate the interplay of two competing factors, namely, enhanced particle aggregation and element-specific surface segregation, on the magnetic properties, with the former boosting and the latter suppressing them. Strong interparticle interactions can lead to a magnetic response different from that of superparamagnetic particles, namely, from canonical spin-glass (0 atom % Cr) to correlated spin-glass (5-15 atom % Cr) behavior below higher spin-glass transition temperatures Tg (20-350 K). The observation of "high-field susceptibility"below cryogenic temperatures (≤20 K) is ascribed to the presence of inhomogeneity/defects caused by Cr segregation. This work emphasizes the necessity of taking into account the delicate balance of such competing factors to understand the magnetic properties of nanoparticulate samples.

Original languageEnglish
Pages (from-to)32883-32889
Number of pages7
JournalACS Omega
Issue number51
StatePublished - 29 Dec 2020
Externally publishedYes


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