It is the distance between the working face of the magnet and
the part with which it is interacting. Often air, but inclusive of other
materials such as coating layer thickness on magnet. If the air gap is enlarged,
the interacted strength will be weakened.
In manufacturing process, the molecule of magnetic material is
aligned by an external magnetic field what process is also called anisotropy or
orientation to obtain the higher magnetic value in the direction of anisotropic
axis. Except AlNiCo magnet is oriented in the process of heat treatment, all
other magnets get anisotropy in the molding process. Magnetizing direction on an
anisotropic magnet only could be along the anisotropic axis. Anisotropic magnet
will output much stronger flux and remanence than isotropic magnet does?
B-H curve /
It is a closed curve obtained for a material by plotting
(usually to rectangular coordinates) corresponding values of magnetic induction
(B) for ordinates and magnetizing force (H) for abscissa when the material is
passing through a complete cycle. In practice, if a magnet is operated in a
static manner with no external fields present, the normal curve is sufficient
for design purposes. When external fields are present, the normal and intrinsic
curves are used to determine the changes in the intrinsic properties of the
It exists when the external flux path of a permanent magnet is
confined with high permeability material.
It is the demagnetizing force required to reduce residual
induction (Br) to zero in a magnetic field after magnetizing to saturation.
It is a temperature point above which the magnet will
completely lose its permanent magnet properties. The Curie temperature is
dependent on magnet composition.
The second quadrant of the hysteresis loop, it completely
characterizes the magnetic properties of the material at a specific temperature.
To get correct demagnetization curve, a specific size sample in compliance with
relevant standard must be used.
It is the ratio of a magnet length to its diameter, or the
diameter of a circle of equivalent cross sectional area. For simple geometries,
such as bars and rods, the dimension ratio is related to the slope of the
operating line of the magnet. On the page with demagnetization curves and the
h:D values are indicated, it is possible to read valid remanence for each h:D
value. With very low h:D ratio, starting with 0.3, these values are only
approximate one. If the magnet is with thin thickness but big length or outside
diameter and in a closed magnetic circuit, then magnet will loss force faster
when the environment temperature is increased.
It indicates the energy that a magnetic material can supply to
an external magnetic circuit when operating at any point on its demagnetization
It expresses the concentration of line of force per unit area
passing from one pole to the other. Magnet material type, dimension ratio, air
gap and position of probe determine the measured value of flux density.
Is that value of H corresponding to the remanent induction
See B-H curve
coercive force (iHc)
Intrinsic coercive force of a material indicates its
resistance to demagnetization. It is equal to the demagnetizing force which
reduces the intrinsic induction in the material to zero after magnetizing to
saturation. It is used to as a measure of resistance to demagnetization, the
higher the figure, the more stable it is.
It is the necessary demagnetizing force to reduce the
intrinsic induction in a magnet to zero after magnetizing to saturation.
The irreversible losses are defined as partial demagnetization
of the magnet, caused by exposure to high or low temperatures, external fields
or other factors, and what are not recoverable when the magnet returns to its
original temperature or other conditions are lifted. Value for irreversible loss
is not definite and is influenced by magnet material, geometric dimension,
operating point and its working magnetic circuit.
Some irreversible losses are recoverable by re-magnetization
and are not recovered when the temperature returns to its original value. These
losses occur when the operating point of the magnet falls below the knee of the
demagnetization curve. The qualified design of permanent magnet should have a
magnetic circuit in which the magnet operates at an operating point above the
knee of the demagnetization curve measured at expected temperature to avoid
performance variations along with temperature change.
Some irreversible losses are not recoverable by
re-magnetization due to metallurgical changes occur in magnets exposed to very
Magnets can be stabilized against irreversible losses by
partial demagnetization induced by temperature cycles or by external magnetic
fields. The resulting lowering of induction must however be accepted.
The magnet what not pre-oriented by an external magnetic field
is called isotropic magnet. Magnetic values measured in any direction or axis of
an isotropic magnet is with no difference. Isotropic magnet could be magnetized
with any preferred pattern what is determined by magnetizing yoke.
Keen of the
It is a point at which the B-H curve ceases to be linear and
starts to be down. One magnet draws different B-H curve and has various keen
when it is working at different temperature. If the operating point of a magnet
falls below the knee, small change of H will result big change of B and the
magnet will suffer irreversible loss of flux. The irreversible flux loss can be
recovered after re-magnetization.
One or several pieces of soft iron that is/are placed on or
between the pole faces of a permanent magnet to decrease the reluctance of the
air gap and thereby reduce the flux leakage from the magnet. It also makes the
magnet less susceptible to demagnetizing influences.
In permanent magnet families except bonded magnets and cast
AlNiCo magnet are all made by powder metallurgic process, so they are lack of
ductility and are very brittle. We strongly recommend careful handle on them and
do not design it as structural parts to avoid chip and being damaged. The
mechanical characteristic of each class magnet is listed on their section
Magnetic circuit is consisted of permanent magnets, pole tips,
air gap and leakage fields.
strength (H) / Magnetizing or demagnetizing force
It is the measure of the vector magnetic quantity that
determines the ability of an electric current, or a magnetic body, to induce a
magnetic field at a given point.
It is a contrived but measurable concept that has evolved in
an attempt to describe the “flow” of a magnetic field. Mathematically, it is the
surface integral of the normal component of the magnetic induction over an area.
Magnetic induction is the magnetic field induced by a field
strength at a given point. It is the vector sum, at each point within the
substance, of the magnetic field strength and resultant intrinsic induction.
Also magnetic induction means flux per unit area normal to the direction of
Product ( (BH)max)
Is the maximum product of (BdHd) which can be obtained on the
demagnetization curve. Using magnet with greater (BH)max value can reduce the
magnet volume if the application is given the same task and other conditions
remain unchanged. The unit of (BH)max is kJ/m3 or MGOe
This is the maximum temperature to which the magnet may be
exposed with no significant long range instability and structural changes. It is
valid for magnets with sufficient large ratios of h:D and free from happening of
demagnetization because of dimension change. On bonded magnet, it is also
dependent on the working temperature of binder.
In the range of working temperature, the remanence and
coercive field strength will back to its original value when the temperature
returns to departure point. In case of out of this working temperature range,
rapid reduction of magnetic strength can occur and new temperature coefficient
has to be reckoned with. There are several factors determine the working
temperature of individual magnet: ratio of dimension h:D and mechanical or
It also called as “axis”, “easy axis” or “angle of
inclination”. The direction in which an anisotropic magnet should be magnetized
in order to achieve optimum magnetic properties is called orientation
It exists when a magnetized magnet is by itself with no
external flux path of high permeability material.
The location on a demagnetizing curve with specific flux
density (B) and field strength values (H) is called operating point. The longer
the magnet is in the direction of anisotropic axis, the nearer the operating
point is at remanence (Br). In the closed magnetic circuit the operating point
corresponds approximately to Br. This is determined by the temperature and
operating conditions as well as the geometry of the magnet.
On account of the temperature coefficient which is basically
negative with rare earth magnets, the operating point is of the great
significance at higher temperature. Magnet with low operating point and / or
opposing magnetic fields can, however suffer persistent loss of magnetization
caused by reduction of coercivity at high temperature. To avoid performance
variations along with temperature change, the qualified design of permanent
magnet should have a magnetic circuit in which the magnet operates at an
operating point above the knee of the demagnetization curve measured at expected
It is used to express the ability of induction to pass through
a material and demonstrate various relationships between magnetic induction (B)
and the field strength (H). For some permanent magnets, its permeability is only
marginally better than air.
It is the reciprocal of the reluctance (R), measured in
maxwells per gilbert.
It is the ratio of the remanent induction (Bd) to a
demagnetizing force (Hd), what is also referred as the operating slope, slope of
the operating line, shear line, load line or B/H of the magnet in open circuit
condition. It is an important data in magnet material selection to ensure
The other elements use to construct an efficient holding
magnet. Both components are mild steel or iron and the purpose of the pole
pieces is to collect the flux from the pole faces and concentrate this to the
point of attachment with the counter-plate. The counter-plate in effect
completes a magnetic circuit.
It is the average slope of the recoil hysteresis loop, also
known as a minor loop.
It is the quantity that determines the magnetic flux resulting
from a given magneto-motive force, somewhat analogous to electrical resistance.
Is any magnetic induction that remains in a magnetic material
after removal of an applied saturating magnetic field, Hs. (Bd is the magnetic
induction at any point on the demagnetization curve; measured in gauss.)
induction / flux density / Remanence (Br)
Is the magnetic induction corresponding to zero magnetizing
force in a magnetic material after saturation in a closed circuit.
Steel or ferrous elements in a magnetic circuit which form a
low reluctance path for the magnetic flux is called return path.
Reversible losses are defined as partial demagnetization of
the magnet, caused by exposure to high or low temperatures, can be recovered
when the magnet returns to its original temperature.
It is a factor which describes the reversible change in a
magnetic property with a change in temperature. The magnetic property
spontaneously returns when the temperature is cycled to its original point. It
is usually expressed as the percentage change per unit of temperature.
It is the abbreviation of “The Restriction of the Use of
Certain Hazardous Substance in Electrical & Electronic Equipment”. According
to European Community directive 2002/95/EC of 27th January 2003, the content of
hazardous material of Pb, Cd, Hg, Cr6+, PBDEs and PBBs in all parts should be
controlled within specified PPM. This directive is effective from 1st July
Slope of the
operating line (Bd/Hd)
See permeance coefficient
To prevent magnetic flux change caused by later external
influences, treatments on a magnet with defined temperature or being
intentionally exposed in a magnetic field are called stabilization.