Iron Nitride Core-Shell Nanoparticles for High Coercivity Magnetization
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Solution Overview
Problem
Iron nitride nanoparticles with high coercivity (Hci>1,000 Oe) exhibit low saturation magnetization (MSat<180 emu/g) due to a non-ferromagnetic shell that dilutes the overall magnetization, and existing deposition methods for thin shells require temperatures exceeding the stability of the α″-Fe16N2 phase, leading to decomposition.
Innovation Solution
Limit the shell thickness to 5 nm or less and ensure a minimum core diameter of at least 20 nm, using non-ferromagnetic materials like FeO, α-Fe2O3, ZnO, Al2O3, SiO2, TiO2, ZrO2, CoO, NiO, Mn, Cr, CrN, Cu, Al, Sn, or Zn to enhance saturation magnetization by limiting dilution and enabling nitridation at lower temperatures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a non-ferromagnetic shell is added to iron nitride nanoparticles to enable nitridation, then the nanoparticles can be manufactured with controlled shell thickness, but the saturation magnetization decreases due to dilution
Solution Approach 1:
The patent applies thin film deposition to create ultra-thin non-ferromagnetic shells (1-10 nm) on iron nitride nanoparticle cores. This thin film approach allows the shell to provide necessary nitridation control while minimizing the volume of non-magnetic material, thereby preserving high saturation magnetization in the core-shell structure
Solution Approach 2:
The patent creates a core-shell structure where the core maintains high magnetic properties (ferromagnetic α''-Fe16N2 phase) and the shell provides controlled nitridation functionality. This local differentiation allows each region to optimize its function: the core maximizes magnetization while the thin shell enables controlled shell formation
2Manufacturing precision
If high temperature deposition methods are used to form thin conformal shells, then uniform shell thickness is achieved, but the α''-Fe16N2 phase decomposes
Solution Approach 1:
The patent changes the temperature parameter from conventional high-temperature deposition (>200°C) to low-temperature deposition (room temperature to 150°C). This parameter change enables the formation of uniform thin conformal shells while preserving the thermally-sensitive α''-Fe16N2 phase structure
Solution Approach 2:
The patent replaces thermal energy-driven deposition with alternative deposition mechanisms that operate at lower temperatures, such as chemical vapor deposition or atomic layer deposition optimized for low-temperature operation, thereby avoiding thermal decomposition of the core phase
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution results in iron nitride nanoparticles with saturation magnetization of at least 180 emu/g and coercivity greater than 1,000 Oe, suitable for high-performance permanent magnets.
Implementation Method 1
a thin material adjacently disposed on the iron-based core, wherein the thin material is configured to enable nitridation of the iron-based core
Data Source
AI summary
Iron nitride nanoparticles and magnet materials made from iron nitride nanoparticles are described. The iron nitride nanoparticles have a core and a shell morphology. The shell is configured to provide a means to nitride the core. The magnetic materials are characterized as having an Msat greater than about 160 emu/g and a coercivity greater than about 700 Oe.