Alnico Magnets

Alnico Magnets: Overview

Alnico megnets, short for Aluminum-Nickel-Cobalt, is one of the earliest permanent magnetic materials, composed of an alloy of aluminum, nickel, cobalt, iron, and trace elements. It was developed in the 1930s and was once the material of choice for permanent magnets, owing to its superior magnetic properties and low-temperature coefficient. Over time, with the advent of ferrite and rare-earth magnets, Alnico’s role in certain applications has diminished but remains essential in high-temperature and specialized uses.

Introduction

Composition: Alnico is a ferrous alloy with aluminum (Al), nickel (Ni), cobalt (Co), and sometimes copper (Cu), titanium (Ti), or other elements added for enhanced magnetic properties.
Properties:
- High coercivity and a Curie temperature exceeding 800°C.
- Produces magnetic fields up to 0.15 Tesla.
Manufacturing: Due to its brittleness and hardness, Alnico is manufactured through casting or sintering.

A notable Alnico alloy, Alnico-6 (8% Al, 16% Ni, 24% Co, 3% Cu, 1% Ti, balance Fe), has a maximum energy product of 3.9 MG·Oe, coercivity of 780 Oe, and a working temperature up to 525°C.

Types of Alnico Magnets

By Manufacturing Method

Cast Alnico:
- Allows production in various shapes and sizes.
- Offers superior magnetic properties.
- Suitable for high-temperature applications.
Sintered Alnico:
- Restricted to smaller dimensions.
- Provides better dimensional tolerances and machinability.
- Magnetic properties are slightly lower than cast Alnico.

By Magnetic Orientation

Isotropic: Equal magnetic properties in all directions.
Anisotropic: Magnetic properties are optimized along a specific direction.

Performance and Grades

Sintered Alnico Grades

Material Grade	Max.Energy Prouct （BH）max		Remanence Br		Intrinsic CoercivityHcj		Coercivity Hcb		Density	Temperature coefficient	Curie Temperature	Remark
Material Grade	Kj/cm3	MGOe	mT	Gs	KA/m	Oe	KA/m	Oe	g/cm3	%/k	Tc ℃
FLN8	8-10	1.0-1.25	520	5200	43	540	40	500	6.7	-0.0020	760	Isotropic
FLNG12	12-14	1.5-1.75	700	7000	43	540	40	500	7.1	-0.014	810
FLNGT18	14-16	1.75-2.0	570	5700	78	980	76	950	7.2	-0.020	850
FLNG28	18-22	2.25-2.75	600	6000	107	1350	95	1200	7.2	-0.020	850	Anisotropic
FLNG34	28-33	3.5-4.15	1050	10500	47	590	46	580	7.2	-0.016	890
FLNGT28	34-38	4.3-4.8	1100	11000	51	640	50	630	7.2	-0.016	850
FLNG38J	38-40	4.75-5.0	730	7300	163	2050	151	1900	7.2	-0.200	850
FLNGT38	38-42	4.75-5.3	800	8000	126	1580	123	1550	7.2	-0.020	850
FLNGT42	42-48	5.3-6.0	880	8800	122	1530	120	1500	7.25	-0.020	850

Cast Alnico Grades

Material Grade	USA Standard Equal to MMPA	Max.Energy Prouct （BH）max		Remanence Br		Coercivity Hcb		Density	Temperature coefficient	Curie Temperature	Remark
Material Grade	USA Standard Equal to MMPA	Kj/cm3	MGOe	mT	Gs	KA/m	Oe	g/cm3	%/k	Tc ℃	Remark
LN9	Alnico1	9.0	1.13	680	6800	30	380	6.9	-0.03	760	Isotropic
LN10	Alnico1	10.0	1.20	600	6000	40	500	6.9		760
LNG12	Alnico2	12.4	1.55	720	7200	45	500	7.0		810
LNG13	Alnico2	13.0	1.60	700	7000	48	600	7.0		810
LNG34	Alnico5	34.0	4.30	1200	12000	48	600	7.3	-0.02	860	Anisotropic
LNG37	Alnico5	37.0	4.65	1200	12000	48	600	7.3
LNG40	Alnico5DG	40.0	5.00	1250	12500	48	600	7.3
LNG44	Alnico5DG	44.0	5.50	1250	12500	52	650	7.3
LNG52	Alnico5-7	52.0	6.50	1300	13000	56	700	7.3
LNGT28	Alnico6	28.0	3.50	1000	10000	58	720	7.3	-0.025	860
LNGT36J	Alnico8H	36.0	4.50	700	7000	140	1750	7.3
LNGT32	Alnico8	32.0	4.0	800	8000	100	1250	7.3
LNGT40	Alnico8	40.0	5.0	800	8000	110	1380	7.3
LNGT60	Alnico9	60.0	7.50	900	9000	110	1380	7.3
LNGT72	Alnico9	72.0	900	1050	10500	112	1400	7.3

Advantages and Disadvantages

Advantages

High Residual Induction: Up to 1.35 T, making Alnico magnets highly effective in maintaining a strong magnetic field.
Excellent Thermal Stability: Low temperature coefficient (-0.02%/°C) and high operating temperatures (up to 600°C).

Disadvantages

Low Coercivity: Typically below 160 KA/m, leading to vulnerability to demagnetization.
Non-linear Demagnetization Curve: Requires careful application design.

Applications

Alnico magnets find use in various industries, including:

Electric Motors
Electric Guitar Pickups
Microphones
Sensors and Speakers
Traveling Wave Tubes (TWTs)
Cow Magnets: Used in agriculture to attract and capture metallic debris in cows’ stomachs.

While Alnico magnets have been largely replaced by rare-earth magnets for many applications, their unique properties make them irreplaceable in high-temperature and specific low-demagnetization settings.