期刊
ACS APPLIED MATERIALS & INTERFACES
卷 14, 期 29, 页码 33491-33504出版社
AMER CHEMICAL SOC
DOI: 10.1021/acsami.2c05558
关键词
magnetic nanoparticles; dead shell effects; colloidal synthesis; small-angle neutron scattering; polarized neutron scattering
资金
- US Department of Energy through the University of Minnesota Center for Quantum Materials [DE-SC-0016371]
- NSF through the MRSEC program [DMR-2010792]
- Center for High Resolution Neutron Scattering
Advances in the synthesis and characterization of colloidal magnetic nanoparticles have provided insights into their complex magnetic behavior and potential applications. This study focuses on the synthesis and characterization of Ni nanoparticles and reveals the presence of a non-ferromagnetic Ni phosphide shell. It also demonstrates bulk-like ferromagnetism in the Ni core and negligible interparticle magnetic interactions. These findings contribute to the understanding of synthesis-structure-property relationships in metallic magnetic nanoparticles and highlight the power of polarized SANS measurement and analysis in magnetic nanoparticle science and technology.
Advances in the synthesis and characterization of colloidal magnetic nanoparticles (NPs) have yielded great gains in the understanding of their complex magnetic behavior, with implications for numerous applications. Recent work using Ni NPs as a model soft ferromagnetic system, for example, achieved quantitative understanding of the superparamagnetic blocking temperature-particle diameter relationship. This hinged, however, on the critical assumption of a ferromagnetic NP volume lower than the chemical volume due to a non ferromagnetic dead shell indirectly deduced from magnetometry. Here, we determine both the chemical and magnetic average internal structures of Ni NP ensembles via unpolarized, half-polarized, and fully polarized small-angle neutron scattering (SANS) measurements and analyses coupled with X-ray diffraction and magnetometry. The postulated nanometric magnetic dead shell is not only detected but conclusively identified as a non-ferromagnetic Ni phosphide derived from the trioctylphosphine commonly used in hot-injection colloidal NP syntheses. The phosphide shell thickness is tunable via synthesis temperature, falling to as little as 0.5 nm at 170 & DEG;C. Temperature-and magnetic field-dependent polarized SANS measurements additionally reveal essentially bulk-like ferromagnetism in the Ni core and negligible interparticle magnetic interactions, quantitatively supporting prior modeling of superparamagnetism. These findings advance the understanding of synthesis-structure-property relationships in metallic magnetic NPs, point to a simple potential route to ligand-free stabilization, and highlight the power of the currently available suite of polarized SANS measurement and analysis capabilities for magnetic NP science and technology.
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