Light Induced Ferromagnetic Magnetic Exchange Coupling in Fe Semiconductor
Citation: Ayush Kumar Narsaria (1993/06/01) Light Induced Ferromagnetic Magnetic Exchange Coupling in Fe Semiconductor. Zeitschrift für Physik B Condensed Matter (RSS)
DOI (original publisher): 10.1007/BF01312168
Semantic Scholar (metadata): 10.1007/BF01312168
Sci-Hub (fulltext): 10.1007/BF01312168
Internet Archive Scholar (search for fulltext): Light Induced Ferromagnetic Magnetic Exchange Coupling in Fe Semiconductor
Download: http://link.springer.com/article/10.1007/BF01312168
Tagged: Chemistry
(RSS)
Summary
Spin Crossover phenomena has attracted much attention these days due to its application in memory storage and optical devices. Spin Crossover is from a low spin state to high spin state. Photo-irradiation in some of the LS transition metal (d4-d7) complexes excites electron from the t2g to eg orbital and intersystem crossing occurs to a HS state which is pretty long lived to induce molecular magnetism.
It is found in this experiment that with E< 2 eV (Band gap of SiO), ferromagnetic exchange takes place between Fe/SiO/Fe trilayer semiconductor depending upon the temperature, SiO layer thickness and light intensity. A special experimental tool called Spin Polarized Secondary Electron Emission (SPSSE) was used for the detection of magnetic exchange in adlayers.
Photo-induced magnetism is studied firstly based on temperature variations. 40 Å thick SiO film was used between 15 Å Fe layers. At temperature of 35 K (, upon irradiation with Nd-YAG laser it was observed that a hysteresis curve is produced suggesting ferromagnetic exchange and having magnitude almost comparable to thermally induced ferromagnetic coupling at temperature of 300 K. It was also observed that there was no temperature increase as low intensity lasers were used, so it can be concluded that the magnetic coupling arises due to electronic excitations while any photochemical and thermal effects are ruled out. However with irradiation of intensity 2W/cm2 or higher the coupling effect can be suppressed completely at both room and lower temperature.
Secondly the magnetic exchange is studied with the variation of the SiO layer thickness. Two experiments were performed. Upon changing the thickness of SiO layer to 55 Å, keeping the temperature at 35 K and 300 K and no irradiation for both the experiments respectively, it was observed that the electronic excitations couldnot lead to magnetic coupling as no hysteresis curve was produced using SPSSE. Upon irradiation of the semiconductor with halogen lamp at 300 K, hysteresis curve was observed using SPSSE but no curve was observed at 35 K. This proves that photon dependent and photon suppressed magnetic exchange coupling largely depends upon the thickness of semiconductor layers.
So it can be concluded that charge carriers in localized states within the band gap mediate the observed magnetic coupling and with higher intensity of irradiation the coupling can be switched off at different temperatures. Photon based excitations are completely based on electronic excitations as the intensity of the source used is not able to increase the temperature of the semiconductor.
Theoretical and Practical Relevance
Photo based magnetic exchange coupling can revolutionize the energy industry and electronic industry. This concept can be used to store energy in its hysteresis curve so produced after its transformation from a paramagnetic state to a ferromagnetic state. This energy can be then be used to power the common electronic instruments. A completely new dimension can be provided in the construction of novel solar cells using photo-induced magnetism.
