Magnetization reversal by circularly polarized light
Encyclopedia
Discovered only recently (2006) by C.D. Stanciu and F. Hansteen and published in Physical Review Letters
this effect is generally called all-optical magnetization reversal. This magnetization reversal technique refers to a method of reversing magnetization in a magnet simply by circularly polarized light and where the magnetization direction is controlled by the light helicity
. In particular, the direction of the angular momentum
of the photons would set the magnetization direction without the need of an external magnetic field
. In fact, this process could be seen as similar to magnetization reversal by spin injection (see also spintronics
). The only difference is that now, the angular momentum is supplied by the circularly polarized photons instead of the polarized electrons.
Although experimentally demonstrated, the mechanism responsible for this all-optical magnetization reversal is not clear yet and remains a subject of debate. Thus, it is not yet clear whether an Inverse Einstein-de Haas effect
is responsible for this switching or a stimulated Raman-like coherent optical scattering process. However, because phenomenologically is the inverse effect of the magneto-optical Faraday effect, magnetization reversal by circularly polarized light is referred to as the inverse Faraday effect.
Early studies in plasmas, paramagnetic solids, dielectric magnetic materials and ferromagnetic semiconductors demonstrated that excitation of a medium with a circularly polarized laser pulse corresponds to the action of an effective magnetic field. Yet, before the experiments of Stanciu and Hansteen, all-optical controllable magnetization reversal in a stable magnetic state was considered impossible.
In quantum field theory and quantum chemistry the effect where the angular momentum associated to the circular motion of the photons induces an angular momentum in the electrons is called photomagneton
. This axial magnetic field with the origins in the angular momentum of the photons has been sometimes refereed in the literature as the field B.
Magnetization reversal by circularly polarized light is the fastest known way to reverse magnetization, and therefore to store data: magnetization reversal is induced on the femtosecond time scale - that translates to a potential of about 100 TBit
/s data storage speeds.
Physical Review Letters
Physical Review Letters , established in 1958, is a peer reviewed, scientific journal that is published 52 times per year by the American Physical Society...
this effect is generally called all-optical magnetization reversal. This magnetization reversal technique refers to a method of reversing magnetization in a magnet simply by circularly polarized light and where the magnetization direction is controlled by the light helicity
Helicity
The term helicity has several meanings. In physics, all referring to a phenomenon that resembles a helix. See:*helicity , the extent to which corkscrew-like motion occurs...
. In particular, the direction of the angular momentum
Angular momentum
In physics, angular momentum, moment of momentum, or rotational momentum is a conserved vector quantity that can be used to describe the overall state of a physical system...
of the photons would set the magnetization direction without the need of an external magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
. In fact, this process could be seen as similar to magnetization reversal by spin injection (see also spintronics
Spintronics
Spintronics , also known as magnetoelectronics, is an emerging technology that exploits both the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-state devices.An additional effect occurs when a spin-polarized current is...
). The only difference is that now, the angular momentum is supplied by the circularly polarized photons instead of the polarized electrons.
Although experimentally demonstrated, the mechanism responsible for this all-optical magnetization reversal is not clear yet and remains a subject of debate. Thus, it is not yet clear whether an Inverse Einstein-de Haas effect
Einstein-de Haas effect
The Einstein–de Haas effect, or the Richardson effect , is a physical phenomenon delineated by Albert Einstein and Wander Johannes de Haas in the mid 1910's, that exposes a relationship between magnetism, angular momentum, and the spin of elementary particles...
is responsible for this switching or a stimulated Raman-like coherent optical scattering process. However, because phenomenologically is the inverse effect of the magneto-optical Faraday effect, magnetization reversal by circularly polarized light is referred to as the inverse Faraday effect.
Early studies in plasmas, paramagnetic solids, dielectric magnetic materials and ferromagnetic semiconductors demonstrated that excitation of a medium with a circularly polarized laser pulse corresponds to the action of an effective magnetic field. Yet, before the experiments of Stanciu and Hansteen, all-optical controllable magnetization reversal in a stable magnetic state was considered impossible.
In quantum field theory and quantum chemistry the effect where the angular momentum associated to the circular motion of the photons induces an angular momentum in the electrons is called photomagneton
Photomagneton
The photomagneton is a theoretical treatment of the unitary group in quantum field theory and quantum chemistry that effectively describes the experimentally observed inverse Faraday effect. When circularly polarized light travels through a plasma, the angular momentum associated to the circular...
. This axial magnetic field with the origins in the angular momentum of the photons has been sometimes refereed in the literature as the field B.
Magnetization reversal by circularly polarized light is the fastest known way to reverse magnetization, and therefore to store data: magnetization reversal is induced on the femtosecond time scale - that translates to a potential of about 100 TBit
Terabit
The terabit is a multiple of the unit bit for digital information or computer storage. The prefix tera is defined in the International System of Units as a multiplier of 1012 , and therefore...
/s data storage speeds.