174
7 Opto-spintronics
combination of magnetic field and optical probe enables us to retrieve a wealth of
information in magnetic materials.
7.6.4 X-ray Probe
Dichroism is the property of a material in which different absorption coefficients
are found when light with different polarization states travels through the medium.
Nowadays, the term dichroism refers to polarization-dependent photon absorption.
Anisotropies in the charge or the spin in the material could be the origin of dichroism.
Latter case is related to magnetic dichroism. Two types of magnetic dichroism techniques, namely linear and circular, are observed in X-ray region. X-ray magnetic
linear dichroism (XMLD) refers the difference in absorption in linearly polarized
perpendicular and parallel to the quantization axis. X-ray magnetic circular dichroism
(XMCD) refers to the difference in absorption for left- and right circularly polarized light. Magnetic properties of ferromagnets (usually metal) are suitably studied
with XMCD whereas antiferromagnets (usually oxides) are studied with XMLD
techniques. Polarized soft X-rays play a pivotal role on studying the origin of fundamental effects such as exchange bias and magnetic anisotropy. The integrated circular
dichroism signal can be used to measure the magnitude of the orbital and spin components of the magnetic moment using sum rules. Time-resolved XMCD measurement
with temporal resolution in sub-picosecond order can provide unique information
into ultrafast light-induced magnetic changes.
7.7 Demagnetization of Metallic Ferromagnets: 3TM
Model
Laser-induced magnetization dynamics experiments confirm that the demagnetization is very complicated and involves different relaxation processes. The interactions
among lattice, electrons and spins can qualitatively be explained with the phenomenological three temperature model (3TM) as given in Fig. 7.8. The said model can be
described by three coupled differential equations assuming certain equilibrium within
the subsystem,
C e d(T e )/dt = −G el (T e −T l ) − G es (T e − T s ) + P(t),
C s d(T s )/dt = −G es (T s − T e ) −G sl (T s − T l ),
C l d(T l )/dt = −G el (T l − T e ) −G sl (T l − T s ),
7 Opto-spintronics
combination of magnetic field and optical probe enables us to retrieve a wealth of
information in magnetic materials.
7.6.4 X-ray Probe
Dichroism is the property of a material in which different absorption coefficients
are found when light with different polarization states travels through the medium.
Nowadays, the term dichroism refers to polarization-dependent photon absorption.
Anisotropies in the charge or the spin in the material could be the origin of dichroism.
Latter case is related to magnetic dichroism. Two types of magnetic dichroism techniques, namely linear and circular, are observed in X-ray region. X-ray magnetic
linear dichroism (XMLD) refers the difference in absorption in linearly polarized
perpendicular and parallel to the quantization axis. X-ray magnetic circular dichroism
(XMCD) refers to the difference in absorption for left- and right circularly polarized light. Magnetic properties of ferromagnets (usually metal) are suitably studied
with XMCD whereas antiferromagnets (usually oxides) are studied with XMLD
techniques. Polarized soft X-rays play a pivotal role on studying the origin of fundamental effects such as exchange bias and magnetic anisotropy. The integrated circular
dichroism signal can be used to measure the magnitude of the orbital and spin components of the magnetic moment using sum rules. Time-resolved XMCD measurement
with temporal resolution in sub-picosecond order can provide unique information
into ultrafast light-induced magnetic changes.
7.7 Demagnetization of Metallic Ferromagnets: 3TM
Model
Laser-induced magnetization dynamics experiments confirm that the demagnetization is very complicated and involves different relaxation processes. The interactions
among lattice, electrons and spins can qualitatively be explained with the phenomenological three temperature model (3TM) as given in Fig. 7.8. The said model can be
described by three coupled differential equations assuming certain equilibrium within
the subsystem,
C e d(T e )/dt = −G el (T e −T l ) − G es (T e − T s ) + P(t),
C s d(T s )/dt = −G es (T s − T e ) −G sl (T s − T l ),
C l d(T l )/dt = −G el (T l − T e ) −G sl (T l − T s ),