Magnetostriction (cf.
electrostriction Electrostriction (cf. magnetostriction) is a property of all electrical non-conductors, or dielectrics, that causes them to change their shape under the application of an electric field.
Explanation
Electrostriction is a property of all dielectri ...
) is a property of
magnetic materials
A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...
that causes them to change their shape or dimensions during the process of
magnetization. The variation of materials' magnetization due to the applied
magnetic field changes the magnetostrictive strain until reaching its saturation value, λ. The effect was first identified in 1842 by
James Joule
James Prescott Joule (; 24 December 1818 11 October 1889) was an English physicist, mathematician and brewer, born in Salford, Lancashire. Joule studied the nature of heat, and discovered its relationship to mechanical work (see energy). T ...
when observing a sample of
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
.
This effect causes energy loss due to frictional heating in susceptible ferromagnetic cores. The effect is also responsible for the low-pitched humming sound that can be heard coming from transformers, where oscillating AC currents produce a changing magnetic field.
Explanation
Internally, ferromagnetic materials have a structure that is divided into ''
domains'', each of which is a region of uniform magnetization. When a magnetic field is applied, the boundaries between the domains shift and the domains rotate; both of these effects cause a change in the material's dimensions. The reason that a change in the magnetic domains of a material results in a change in the material's dimensions is a consequence of
magnetocrystalline anisotropy
In physics, a ferromagnetic material is said to have magnetocrystalline anisotropy if it takes more energy to magnetize it in certain directions than in others. These directions are usually related to the principal axes of its crystal lattice. I ...
; it takes more energy to magnetize a crystalline material in one direction than in another. If a magnetic field is applied to the material at an angle to an easy axis of magnetization, the material will tend to rearrange its structure so that an easy axis is aligned with the field to minimize the
free energy of the system. Since different crystal directions are associated with different lengths, this effect induces a
strain
Strain may refer to:
Science and technology
* Strain (biology), variants of plants, viruses or bacteria; or an inbred animal used for experimental purposes
* Strain (chemistry), a chemical stress of a molecule
* Strain (injury), an injury to a mu ...
in the material.
The reciprocal effect, the change of the magnetic susceptibility (response to an applied field) of a material when subjected to a mechanical stress, is called the
Villari effect The inverse magnetostrictive effect, magnetoelastic effect or Villari effect, after its discoverer Emilio Villari, is the change of the magnetic susceptibility of a material when subjected to a mechanical stress.
Explanation
The magnetostriction ...
. Two other effects are related to magnetostriction: the
Matteucci effect is the creation of a helical anisotropy of the susceptibility of a magnetostrictive material when subjected to a
torque
In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
and the
Wiedemann effect is the twisting of these materials when a helical magnetic field is applied to them.
The Villari reversal is the change in sign of the magnetostriction of
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
from positive to negative when exposed to magnetic fields of approximately 40
kA/m.
On magnetization, a magnetic material undergoes changes in volume which are small: of the order 10
−6.
Magnetostrictive hysteresis loop
![Magnetostrictive hysteresis loop of Mn-Zn ferrite](https://upload.wikimedia.org/wikipedia/commons/8/8b/Magnetostrictive_hysteresis_loop_of_Mn-Zn_ferrite.png)
Like
flux density, the magnetostriction also exhibits
hysteresis versus the strength of the magnetizing field. The shape of this hysteresis loop (called "dragonfly loop") can be reproduced using the
Jiles-Atherton model.
Magnetostrictive materials
Magnetostrictive materials can convert magnetic energy into
kinetic energy
In physics, the kinetic energy of an object is the energy that it possesses due to its motion.
It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acc ...
, or the reverse, and are used to build
actuators and
sensors. The property can be quantified by the magnetostrictive coefficient, λ, which may be positive or negative and is defined as the fractional change in length as the magnetization of the material increases from zero to the
saturation
Saturation, saturated, unsaturation or unsaturated may refer to:
Chemistry
* Saturation, a property of organic compounds referring to carbon-carbon bonds
**Saturated and unsaturated compounds
** Degree of unsaturation
**Saturated fat or fatty aci ...
value. The effect is responsible for the familiar "
electric hum" () which can be heard near
transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
s and high power electrical devices.
Cobalt exhibits the largest room-temperature magnetostriction of a pure element at 60
microstrain
In physics, deformation is the continuum mechanics transformation of a body from a ''reference'' configuration to a ''current'' configuration. A configuration is a set containing the positions of all particles of the body.
A deformation can ...
s. Among alloys, the highest known magnetostriction is exhibited by
Terfenol-D
Terfenol-D, an alloy of the formula (''x'' ≈ 0.3), is a magnetostrictive material. It was initially developed in the 1970s by the Naval Ordnance Laboratory in the United States. The technology for manufacturing the material efficiently was d ...
, (Ter for
terbium
Terbium is a chemical element with the symbol Tb and atomic number 65. It is a silvery-white, rare earth metal that is malleable, and ductile. The ninth member of the lanthanide series, terbium is a fairly electropositive metal that reacts with w ...
, Fe for
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
, NOL for
Naval Ordnance Laboratory
The Naval Ordnance Laboratory (NOL) was a facility in the White Oak area of Montgomery County, Maryland. It is now used as the headquarters of the U.S. Food and Drug Administration.
Origins
The U.S. Navy Mine Unit, later the Mine Laboratory at ...
, and D for
dysprosium
Dysprosium is the chemical element with the symbol Dy and atomic number 66. It is a rare-earth element in the lanthanide series with a metallic silver luster. Dysprosium is never found in nature as a free element, though, like other lanthanides, ...
). Terfenol-D, , exhibits about 2,000 microstrains in a field of 160 kA/m (2 kOe) at room temperature and is the most commonly used engineering magnetostrictive material.
Galfenol In materials science, galfenol is the general term for an alloy of iron and gallium. The name was first given to iron-gallium alloys by United States Navy researchers in 1998 when they discovered that adding gallium to iron could amplify iron's ...
, , and
Alfer, , are newer alloys that exhibit 200-400 microstrains at lower applied fields (~200 Oe) and have enhanced mechanical properties from the brittle Terfenol-D. Both of these alloys have <100> easy axes for magnetostriction and demonstrate sufficient ductility for sensor and actuator applications.
![Magnetostrictive flow sensor](https://upload.wikimedia.org/wikipedia/commons/c/c4/Magnetostrictive_flow_sensor.png)
Another very common magnetostrictive composite is the amorphous alloy with its trade name
Metglas
Metglas is a thin amorphous metal alloy ribbon produced by using rapid solidification process of approximately . This rapid solidification creates unique ferromagnetic properties that allows the ribbon to be magnetized and de-magnetized quickly an ...
2605SC. Favourable properties of this material are its high saturation-magnetostriction constant, λ, of about 20
microstrain
In physics, deformation is the continuum mechanics transformation of a body from a ''reference'' configuration to a ''current'' configuration. A configuration is a set containing the positions of all particles of the body.
A deformation can ...
s and more, coupled with a low
magnetic-anisotropy field strength, H
A, of less than 1 kA/m (to reach
magnetic saturation
Seen in some magnetic materials, saturation is the state reached when an increase in applied external magnetic field ''H'' cannot increase the magnetization of the material further, so the total magnetic flux density ''B'' more or less levels off ...
).
Metglas
Metglas is a thin amorphous metal alloy ribbon produced by using rapid solidification process of approximately . This rapid solidification creates unique ferromagnetic properties that allows the ribbon to be magnetized and de-magnetized quickly an ...
2605SC also exhibits a very strong ΔE-effect with reductions in the effective
Young's modulus
Young's modulus E, the Young modulus, or the modulus of elasticity in tension or compression (i.e., negative tension), is a mechanical property that measures the tensile or compressive stiffness of a solid material when the force is applied le ...
up to about 80% in bulk. This helps build energy-efficient magnetic
MEMS
Microelectromechanical systems (MEMS), also written as micro-electro-mechanical systems (or microelectronic and microelectromechanical systems) and the related micromechatronics and microsystems constitute the technology of microscopic devices, ...
.
Cobalt
ferrite, (CoO·Fe
2O
3), is also mainly used for its magnetostrictive applications like sensors and actuators, thanks to its high saturation magnetostriction (~200 parts per million). In the absence of
rare-earth
The rare-earth elements (REE), also called the rare-earth metals or (in context) rare-earth oxides or sometimes the lanthanides (yttrium and scandium are usually included as rare earths), are a set of 17 nearly-indistinguishable lustrous silve ...
elements, it is a good substitute for
Terfenol-D
Terfenol-D, an alloy of the formula (''x'' ≈ 0.3), is a magnetostrictive material. It was initially developed in the 1970s by the Naval Ordnance Laboratory in the United States. The technology for manufacturing the material efficiently was d ...
. Moreover, its magnetostrictive properties can be tuned by inducing a magnetic uniaxial anisotropy. This can be done by magnetic annealing, magnetic field assisted compaction, or reaction under uniaxial pressure. This last solution has the advantage of being ultrafast (20 min), thanks to the use of
spark plasma sintering Spark plasma sintering (SPS), also known as field assisted sintering technique (FAST) or pulsed electric current sintering (PECS), or plasma pressure compaction (P2C) is a sintering technique.
The main characteristic of SPS is that the pulsed or u ...
.
In early
sonar
Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigation, navigate, measure distances (ranging), communicate with or detect o ...
transducers during World War II,
nickel
Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow to ...
was used as a magnetostrictive material. To alleviate the shortage of nickel, the Japanese navy used an
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
-
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
alloy from the
Alperm Alperm (also alfenol or alfer) is a class of alloys comprising 83-90% of iron and 10-17% of aluminium. The most widely used composition is with 16% Al.
An alloy with 13% Al is also sometimes referred to as alfer. It exhibits large magnetostrictio ...
family.
Mechanical behaviors of magnetostrictive alloys
Effect of microstructure on elastic strain
Single-crystal
In materials science, a single crystal (or single-crystal solid or monocrystalline solid) is a material in which the crystal lattice of the entire sample is continuous and unbroken to the edges of the sample, with no grain boundaries
In m ...
alloys exhibit superior microstrain, but are vulnerable to yielding due to the anisotropic mechanical properties of most metals. It has been observed that for
polycrystalline
A crystallite is a small or even microscopic crystal which forms, for example, during the cooling of many materials. Crystallites are also referred to as grains.
Bacillite is a type of crystallite. It is rodlike with parallel longulites.
Stru ...
alloys with a high area coverage of preferential grains for microstrain, the mechanical properties (
ductility
Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...
) of magnetostrictive alloys can be significantly improved. Targeted metallurgical processing steps promote
abnormal grain growth
Abnormal or discontinuous grain growth, also referred to as exaggerated or secondary recrystallisation grain growth, is a grain growth phenomenon through which certain energetically favorable grains ( crystallites) grow rapidly in a matrix of fin ...
of grains in
galfenol In materials science, galfenol is the general term for an alloy of iron and gallium. The name was first given to iron-gallium alloys by United States Navy researchers in 1998 when they discovered that adding gallium to iron could amplify iron's ...
and
alfenol thin sheets, which contain two easy axes for magnetic domain alignment during magnetostriction. This can be accomplished by adding particles such as
boride A boride is a compound between boron and a less electronegative element, for example silicon boride (SiB3 and SiB6). The borides are a very large group of compounds that are generally high melting and are covalent more than ionic in nature. Some bo ...
species and
niobium
Niobium is a chemical element with chemical symbol Nb (formerly columbium, Cb) and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has sim ...
carbide () during initial chill casting of the
ingot
An ingot is a piece of relatively pure material, usually metal, that is cast into a shape suitable for further processing. In steelmaking, it is the first step among semi-finished casting products. Ingots usually require a second procedure of sha ...
.
For a polycrystalline alloy, an established formula for the magnetostriction, λ, from known directional microstrain measurements is:
λ
s = 1/5(2λ
100+3λ
111)
![Tensiletestgallium](https://upload.wikimedia.org/wikipedia/commons/1/1c/Tensiletestgallium.png)
During subsequent
hot rolling
In metalworking, rolling is a metal forming process in which metal stock is passed through one or more pairs of rolls to reduce the thickness, to make the thickness uniform, and/or to impart a desired mechanical property. The concept is simil ...
and
recrystallization steps, particle strengthening occurs in which the particles introduce a “pinning” force at
grain boundaries
In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are two-dimensional defects in the crystal structure, and tend to decrease the electrical and thermal ...
that hinders normal (
stochastic
Stochastic (, ) refers to the property of being well described by a random probability distribution. Although stochasticity and randomness are distinct in that the former refers to a modeling approach and the latter refers to phenomena themselv ...
) grain growth in an annealing step assisted by a atmosphere. Thus, single-crystal-like texture (~90% grain coverage) is attainable, reducing the interference with
magnetic domain
A magnetic domain is a region within a magnetic material in which the magnetization is in a uniform direction. This means that the individual magnetic moments of the atoms are aligned with one another and they point in the same direction. When c ...
alignment and increasing microstrain attainable for polycrystalline alloys as measured by semiconducting
strain gauges. These surface textures can be visualized using
electron backscatter diffraction (EBSD) or related diffraction techniques.
Compressive stress to induce domain alignment
For actuator applications, maximum rotation of magnetic moments leads to the highest possible magnetostriction output. This can be achieved by processing techniques such as stress annealing and field annealing. However, mechanical pre-stresses can also be applied to thin sheets to induce alignment perpendicular to actuation as long as the stress is below the buckling limit. For example, it has been demonstrated that applied compressive pre-stress of up to ~50 MPa can result in an increase of magnetostriction by ~90%. This is hypothesized to be due to a "jump" in initial alignment of domains perpendicular to applied stress and improved final alignment parallel to applied stress.
Constitutive behavior of magnetostrictive materials
These materials generally show non-linear behavior with a change in applied magnetic field or stress. For small magnetic fields, linear piezomagnetic constitutive behavior is enough. Non-linear magnetic behavior is captured using a classical macroscopic model such as the
Preisach model Originally, the Preisach model of hysteresis generalized magnetic hysteresis as the relationship between the magnetic field and magnetization of a magnetic material as the parallel connection of independent relay ''hysterons''. It was first suggeste ...
and Jiles-Atherton model. For capturing magneto-mechanical behavior, Armstrong proposed an "energy average" approach. More recently, Wahi ''et al.''
have proposed a computationally efficient
constitutive model wherein constitutive behavior is captured using a "locally linearizing" scheme.
Applications
*
Electronic article surveillance
Electronic article surveillance is a technological method for preventing shoplifting from retail stores, pilferage of books from libraries or removal of properties from office buildings. Special tags are fixed to merchandise; these tags are remove ...
– using magnetostriction to prevent
shoplifting
Shoplifting is the theft of goods from an open retail establishment, typically by concealing a store item on one's person, in pockets, under clothes or in a bag, and leaving the store without paying. With clothing, shoplifters may put on items ...
*
Magnetostrictive delay lines - an earlier form of computer memory
* Magnetostrictive
loudspeakers
A loudspeaker (commonly referred to as a speaker or speaker driver) is an electroacoustic transducer that converts an electrical audio signal into a corresponding sound. A ''speaker system'', also often simply referred to as a "speaker" or "l ...
and
headphones
Headphones are a pair of small loudspeaker drivers worn on or around the head over a user's ears. They are electroacoustic transducers, which convert an electrical signal to a corresponding sound. Headphones let a single user listen to an au ...
See also
*
Electromagnetically induced acoustic noise and vibration
Electromagnetically induced acoustic noise (and vibration), electromagnetically excited acoustic noise, or more commonly known as coil whine, is audible sound directly produced by materials vibrating under the excitation of electromagnetic forc ...
*
Inverse magnetostrictive effect
*
Wiedemann effect – a torsional force caused by magnetostriction
*
Magnetomechanical effects for a collection of similar effects
*
Magnetocaloric effect
Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This technique can be used to attain extremely low temperatures, as well as the ranges used in common refrigerators.
A magnetocaloric material warms up when a m ...
*
Electrostriction Electrostriction (cf. magnetostriction) is a property of all electrical non-conductors, or dielectrics, that causes them to change their shape under the application of an electric field.
Explanation
Electrostriction is a property of all dielectr ...
*
Piezoelectricity
Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress. The word ''p ...
*
Piezomagnetism Piezomagnetism is a phenomenon observed in some antiferromagnetic and ferrimagnetic crystals. It is characterized by a linear coupling between the system's magnetic polarization and Strain (materials science), mechanical strain. In a piezomagnetic m ...
*
SoundBug
Soundbug is a small speaker that can turn a resonant flat surface into a flat panel speaker. The Soundbug is attached to a smooth resonant surface, this surface then acts as speaker. The tone differs depending on the surface (wood, metal, glass etc ...
*
FeONIC
Feonic is a commercial company specialising in the design and development of magnetostrictive audio products and is a spin-off from Hull University.
Products
The products use a smart material that changes shape in a magnetic field. This mater ...
– developer of audio products using magnetostriction
*
Terfenol-D
Terfenol-D, an alloy of the formula (''x'' ≈ 0.3), is a magnetostrictive material. It was initially developed in the 1970s by the Naval Ordnance Laboratory in the United States. The technology for manufacturing the material efficiently was d ...
*
Galfenol In materials science, galfenol is the general term for an alloy of iron and gallium. The name was first given to iron-gallium alloys by United States Navy researchers in 1998 when they discovered that adding gallium to iron could amplify iron's ...
References
External links
Magnetostriction*
Invisible Speakers from Feonic that use MagnetostrictionMagnetostrictive alloy maker: REMA-CN
{{Authority control
Magnetic ordering