Editing Magnetic core (section)

===Powdered metals===
Powder cores consist of metal grains mixed with a suitable organic or inorganic binder, and pressed to desired density. Higher density is achieved with higher pressure and lower amount of binder. Higher density cores have higher permeability, but lower resistance and therefore higher losses due to eddy currents. Finer particles allow operation at higher frequencies, as the eddy currents are mostly restricted to within the individual grains. Coating of the particles with an insulating layer, or their separation with a thin layer of a binder, lowers the eddy current losses. Presence of larger particles can degrade high-frequency performance. Permeability is influenced by the spacing between the grains, which form distributed air gap; the less gap, the higher permeability and the less-soft saturation. Due to large difference of densities, even a small amount of binder, weight-wise, can significantly increase the volume and therefore intergrain spacing.

Lower permeability materials are better suited for higher frequencies, due to balancing of core and winding losses.

The surface of the particles is often oxidized and coated with a phosphate layer, to provide them with mutual electrical insulation.

==== Iron ====
Powdered iron is the cheapest material. It has higher core loss than the more advanced alloys, but this can be compensated for by making the core bigger; it is advantageous where cost is more important than mass and size. Saturation flux of about 1 to 1.5 tesla. Relatively high hysteresis and eddy current loss, operation limited to lower frequencies (approx. below 100&nbsp;kHz). Used in energy storage inductors, DC output chokes, differential mode chokes, triac regulator chokes, chokes for [[power factor]] correction, resonant inductors, and pulse and flyback transformers.<ref name="coilws"/>

The binder used is usually epoxy or other organic resin, susceptible to thermal aging. At higher temperatures, typically above 125&nbsp;°C, the binder degrades and the core magnetic properties may change. With more heat-resistant binders the cores can be used up to 200&nbsp;°C.<ref name="chalmers">{{cite web|author=Johan Kindmark, Fredrik Rosén |url=http://publications.lib.chalmers.se/records/fulltext/183920/183920.pdf |title=Powder Material for Inductor Cores, Evaluation of MPP, Sendust and High flux core characteristics |publisher=Department of Energy and Environment, Division of Electric Power Engineering, Chalmers University of Technology |location=Göteborg, Sweden |date=2013 |access-date=2017-06-05}}</ref>

Iron powder cores are most commonly available as toroids. Sometimes as E, EI, and rods or blocks, used primarily in high-power and high-current parts.

Carbonyl iron is significantly more expensive than hydrogen-reduced iron.

==== Carbonyl iron ====
{{main article|carbonyl iron}}

Powdered cores made of [[carbonyl iron]], a highly pure iron, have high stability of parameters across a wide range of [[temperature]]s and [[magnetic flux]] levels, with excellent [[Q factor]]s between 50&nbsp;kHz and 200&nbsp;MHz. Carbonyl iron powders are basically constituted of micrometer-size [[sphere]]s of iron coated in a thin layer of [[electrical insulation]]. This is equivalent to a microscopic laminated magnetic circuit (see silicon steel, above), hence reducing the [[eddy currents]], particularly at very high frequencies. Carbonyl iron has lower losses than hydrogen-reduced iron, but also lower permeability.

A popular application of carbonyl iron-based magnetic cores is in high-frequency and broadband [[inductor]]s and [[transformer]]s, especially higher power ones.

Carbonyl iron cores are often called "RF cores".

The as-prepared particles, "E-type"and have onion-like skin, with concentric shells separated with a gap. They contain significant amount of carbon. They behave as much smaller than what their outer size would suggest. The "C-type" particles can be prepared by heating the E-type ones in hydrogen atmosphere at 400&nbsp;°C for prolonged time, resulting in carbon-free powders.<ref name="handbkferr"/>

==== Hydrogen-reduced iron ====
Powdered cores made of [[hydrogen reduced iron]] have higher permeability but lower Q than carbonyl iron. They are used mostly for [[electromagnetic interference]] [[electronic filter|filters]] and low-frequency chokes, mainly in [[switched-mode power supply|switched-mode power supplies]].

Hydrogen-reduced iron cores are often called "power cores".

==== MPP (molypermalloy) ====
An alloy of about 2% [[molybdenum]], 81% [[nickel]], and 17% iron. Very low core loss, low hysteresis and therefore low signal distortion. Very good temperature stability. High cost. Maximum saturation flux of about 0.8 tesla. Used in high-Q filters, resonant circuits, loading coils, transformers, chokes, etc.<ref name="coilws">{{cite web|url=http://www.coilws.com/index.php?main_page=page&id=41|title=How to choose Iron Powder, Sendust, Koolmu, High Flux and MPP Cores as output inductor and chokes : CWS Coil Winding Specialist, manufacturer of transformers, inductors, coils and chokes|first=The Zen Cart™ Team and|last=others|website=www.coilws.com}}</ref>

The material was first introduced in 1940, used in [[loading coil]]s to compensate capacitance in long telephone lines. It is usable up to about 200&nbsp;kHz to 1&nbsp;MHz, depending on vendor.<ref name="chalmers"/> It is still used in above-ground telephone lines, due to its temperature stability. Underground lines, where temperature is more stable, tend to use ferrite cores due to their lower cost.<ref name="handbkferr">{{cite book|url=https://books.google.com/books?id=StbgBwAAQBAJ&dq=powder+core+%22carbonyl+iron%22&pg=PA185|title=Handbook of Modern Ferromagnetic Materials|first=Alex|last=Goldman|date=6 December 2012|publisher=Springer Science & Business Media|via=Google Books|isbn=9781461549178}}</ref>

==== High-flux (Ni-Fe) ====
An alloy of about 50–50% of nickel and iron. High energy storage, saturation flux density of about 1.5 tesla. Residual flux density near zero. Used in applications with high DC current bias (line noise filters, or inductors in switching regulators) or where low residual flux density is needed (e.g. pulse and flyback transformers, the high saturation is suitable for unipolar drive), especially where space is constrained. The material is usable up to about 200&nbsp;kHz.<ref name="coilws"/>

==== Sendust, KoolMU ====
An alloy of 6% aluminium, 9% silicon, and 85% iron. Core losses higher than MPP. Very low [[magnetostriction]], makes low audio noise. Loses inductance with increasing temperature, unlike the other materials; can be exploited by combining with other materials as a composite core, for temperature compensation. Saturation flux of about 1 tesla. Good temperature stability. Used in switching power supplies, pulse and flyback transformers, in-line noise filters, swing chokes, and in filters in [[phase-fired controller]]s (e.g. dimmers) where low acoustic noise is important.<ref name="coilws"/>

Absence of nickel results in easier processing of the material and its lower cost than both high-flux and MPP.

The material was invented in Japan in 1936. It is usable up to about 500&nbsp;kHz to 1&nbsp;MHz, depending on vendor.<ref name="chalmers"/>

==== Nanocrystalline ====

A [[nanocrystalline]] alloy of a standard iron-boron-silicon alloy, with addition of smaller amounts of [[copper]] and [[niobium]]. The grain size of the powder reaches down to 10–100 nanometers. The material has very good performance at lower frequencies. It is used in chokes for inverters and in high power applications. It is available under names like e.g. Nanoperm, Vitroperm, Hitperm and Finemet.<ref name="chalmers"/>