Nanocrystalline and amorphous cores are the two leading high-performance soft magnetic materials for transformers, chokes, and current sensors. Both are produced by rapid solidification of molten alloy, but they differ in microstructure, magnetic properties, and cost. Choosing between a nanocrystalline core and an amorphous core depends on your frequency, core loss budget, saturation requirement, and temperature range. This guide compares the two materials and helps you decide.
How the Two Materials Are Made
Amorphous cores (metallic glass) are made by cooling molten metal so fast that atoms do not form a crystal lattice — the material is a frozen liquid structure. Common alloys include iron-based (e.g., Fe-Si-B) with high saturation flux density, and cobalt-based with very high permeability but higher cost.
Nanocrystalline cores start as amorphous ribbons and are then annealed to precipitate nanometre-sized grains (about 10-30 nm) of iron-silicon in an amorphous matrix. The result is a material that combines the best of amorphous (high saturation) and crystalline (low loss, high permeability) behaviour. The most common nanocrystalline alloy is Fe-based (e.g., Fe-Cu-Nb-Si-B, brand names such as Finemet or Vitroperm).
Nanocrystalline vs Amorphous: Comparison Table
| Parameter | Amorphous (Fe-based) | Nanocrystalline |
|---|---|---|
| Initial permeability | ~5,000-10,000 | ~20,000-80,000 (up to 200,000 in toroids) |
| Saturation flux density | ~1.5-1.6 T (Fe-based) | ~1.2-1.25 T |
| Core loss | Low, but higher than nanocrystalline | Lowest — comparable to the best ferrite at medium frequency |
| Permeability stability vs temperature | Good | Excellent (Curie temperature ~570-600 °C) |
| Operating frequency | 50 Hz – ~50 kHz | Up to ~100 kHz (some designs to 200 kHz+) |
| Relative cost | Lower | Higher (annealing + tighter control) |
| Typical uses | Distribution transformers, current transformers, reactors | EMI chokes, common mode chokes, CTs, high-performance transformers |
Key Differences Explained
1. Permeability. Nanocrystalline cores offer permeability several times higher than amorphous cores. For common mode chokes, this means far more impedance per turn — fewer turns, less copper, and a smaller choke for the same attenuation.
2. Core loss. At frequencies above a few kHz, nanocrystalline cores have the lowest loss among metallic soft magnetic materials. This translates into cooler, more efficient transformers and chokes at switching frequencies.
3. Saturation flux density. Iron-based amorphous cores saturate around 1.5-1.6 T — higher than nanocrystalline (1.2-1.25 T). If the design is dominated by DC bias or requires maximum flux swing (e.g., large power transformers at line frequency), amorphous may be the better fit.
4. Cost. Amorphous cores are cheaper to produce; nanocrystalline requires controlled annealing and tighter material tolerances, raising the price. For high-volume, cost-sensitive line-frequency transformers, amorphous often wins.
How to Choose Between Them
Choose nanocrystalline when: you need maximum permeability per size (compact common mode chokes and current transformers), the design runs at 10-100 kHz where core loss matters, or you need a wide operating temperature range with stable permeability. Nanocrystalline is the premium choice for high-end EMI chokes and precision CTs.
Choose amorphous when: you need the highest saturation flux density at low frequency, cost is the priority for line-frequency power transformers (e.g., amorphous distribution transformers), or the application tolerates the lower permeability. Amorphous cores are also a strong choice for fault-current-handling CTs where saturation must be delayed.
Sirui Nanocrystalline Core Solutions
Shaanxi SiRui Technology Co., Ltd manufactures nanocrystalline cores and amorphous cores for common mode chokes, current transformers, and high-performance transformers. Our nanocrystalline series covers toroidal cores with permeability up to 100,000+, custom strip-wound cores, and complete wound components. All products are ISO 9001:2015 certified and RoHS / REACH compliant.
For more background, read our Nanocrystalline Core: Properties, Benefits & Selection Guide, Transformer Core Materials Selection Guide, and High Current Common Mode Choke Design Guide. Contact sales@sirui-tech.com for a material selection review.
FAQ
Is nanocrystalline better than amorphous?
Not universally. Nanocrystalline wins on permeability, high-frequency core loss, and temperature stability; amorphous wins on saturation flux density at line frequency and on cost. The right choice depends on the operating frequency, size target, and budget.
Why are nanocrystalline cores so popular for common mode chokes?
Their very high permeability gives maximum impedance per turn, so the choke needs fewer turns, less copper, and a smaller footprint — while keeping low core loss across the conducted emissions band.
Can amorphous cores handle high frequency?
Iron-based amorphous cores work well up to about 50 kHz; above that, core loss rises faster than nanocrystalline. Cobalt-based amorphous cores reach higher frequencies but are expensive. For switching frequencies above 50 kHz, nanocrystalline is usually the better engineering choice.