Iron-Based nanocrystalline materials have enjoyed increased acceptance in modern electronic designs only in the past few years.  Nanocrystalline materials have a proven record of high performance, there has been improved reliability in the manufacturing process and this material is now available from multiple sources.

Nanocrystalline soft magnetic materials are now superior to permalloys, ferrites and even amorphous cobalt based alloys in a growing range of applications.  The table below identifies different properties of the various soft magnetic materials that are available today.
General Specifications:
Saturation Flux Density 1,200 mT
Permeability 25,000—90,000 @ 10KHz
Saturation Magnetostriction < 0.5 ppm
Spec. Electrical Resistivity 115  μΏcm
Density 7.35 g/cm3
Curie Temperature 600°C
Max. Operating Temperature 120°C
Core Losses (100KHz, 300mT, sine wave) > 110 W/kg
Alloy Composition Fe:73.5,Cu:1,Nb:3,Si:15.5,B:7

Nanocrystalline vs. other alloys

Material Alloy
Composition

Strip
Thickness
(µm)

 Losses
(20KHz 200mT) (W/Kg)		 Saturation
Bsat (mT)		 Magnetostriction
λs (10-6)		 Permeability
(50Hz)
Nanocrystalline Alloys FE 73 (Si,B) 24 20 4 1,200 0.1 20,000-200,000
Standard Crystalline Permalloy Ni 60 Fe 40 50 45 1,200 10 20,000-30,000
Advanced Crystalline Alloy Fe 93.5 Si 6.5 50 40 1,300 0.1 16,000
Amorphous Alloys FE 76 (Si,B) 24 25 18 1,500 25 6,500-8,000
High Performance Ferrite MnZn - 17 500 - 1,000-30,000
Advanced Crystalline Permalloy NI 80 FE 20 30 14 800 1 100,000-300,000
Amorphous Alloy IIa Co 73 (Si,B) 27 25 5 550 < 0.2 100,000-150,000
Amorphous Alloy IIb Co 77 (Si,B) 23 25 6.5 1,000 < 0.2 2,000-4,500
Amorphous Alloy IIc Co 80 (Si,B) 20 25 6.5 1,000 < 0.2 1,000-2,500

Applications:

By variation of the annealing parameters, the required properties such as shape of the B/H-Loop and permeability can be adjusted in a wide range (See figure below). As a result, the spectrum of applications in power electronics ranges from chokes and filters to power transformers.

hpgraph
Graph demonstrating the variable range of Hysteresis Loops and Permeability Levels

Benefits

Nanocrystalline over ferrite or permalloy:

  1. Significant Reduction of Build Volume of Inductive Component
  2. Less Heat Dissipation due to Reduced Number of Turns
  3. Stable Operation in a Temperature Range of –25 to +120°C.
  4. Larger Safety Margins
  5. Variable Toroidal Geometries—Tooling costs may apply

The primary application for the nanocrystalline material so far is common mode chokes for EMI Off-line (Mains) filters for any kind of switched mode power converters and inverter drives. Here the most significant design consideration is the reduction of build volume achieved because of both relevant material parameters (permeability and flux swing) are significantly higher then with Ferrite.

The second primary application is common mode chokes specifically designed to reduce EMI voltage spikes in Inverter Drive Motor Systems.

Secondary mainstream applications:

  1. Power transformers in push-pull converters (full wave) from a few hundred watts to several KW
  2. Trigger transformers for IGBT-driven converters
  3. Current Transformers
  4. Transformers for Passive Earth Leakage Circuit Breakers (Europe primarily)