We know that electron will be spinning on its axis. The spin can be parallel or anti – parallel. This spin degree can be used to change the way data is changed or carried. This field of tronics which we in addition to charge of electron, also use the spin of electrons is called SPINTRONICS. Use of the spin provides additional functionalities with increased speed.
The figure above explains the concept of Spintronics. It shows that the basic properties of the electrons such as spin, charge, photon is used for data manipulation and storage. The interaction between spin, charge, and photon opens a new field called spintronics.
Now, let us see the main differences between electronics ad spintronics. In present electronics, each function required is designed and fabricated in separate chips and these chips are interconnected to obtain desired functionalities. For example, in order to store the data we will use memory unit, to process data we use processor and to transmit/receive data we may use optical fiber.
But, in the case of spintronics basic properties of electron itself is used hence providing multi – functionalities the properties of electrons used for different functions are:
Spin -> Data
Charge -> Processing
Photon -> Transmission
RESEARCH AREAS :
The scientist have been performing research on some of the field related to spin of electron which will help us to realize the spin devices and spin application into the real world and replace present electronics. The fields of research are:-
- Creation of spin polarization through optical OR magnetic injection.
- Spin polarization transport through semiconductors and super conductor interface.
- Spin relaxation in semiconductors.
- Spin based devices such as PN-junction and amplifiers.
- Spin based quantum computing.
- Feasibility of using phosphorous donor nuclear spins in Si for the purpose of quantum computing and in particular whether SET [Single electron Transistor] can be effectively used as a single electron spin detector.
- Use of NSOM [Near field Scanning Optical Microscopy] to detect electrons in semiconductor quantum dots.
- To detect electron spins using transport experiments, whether electron spin entanglement can be measured using noise correlation
measurements, and whether electron spins trapped in gated quantum dots can be used as qubits.
Once the above researches are completed we can start using spin devices. The above fields of research can be understood by analyzing the figure below.
The figure in the left shows the spin polarization of electrons in the case of semiconductors and a ferromagnetic material. We are not concerned about spin in semiconductor but we are concerned in the case of ferromagnetic materials.
The figure in the right shows one of the two basic spin devices called MTJ [Magnetic Tunnel Junction]. The MTJ is a device with two ferromagnetic structure separated by a silicon layer.
The electron will tunnel from one layer of ferro – magnet to other. The tunneling factor is dependent on the spin of electrons of both he layers. If the spin of the electrons are in the same direction then the tunneling will be high and if the spin direction is I opposite direction then the tunneling is low.
The MTJ can be used as a PN-junction, the forward bias of the PN-junction is achieved when spin of the electrons are in the same direction and reverse bias is achieved when spin of the electrons are in opposite direction.
The proper operation of PN-junction requires the spin of the electron to change as a function of real-time. This can be achieved by using optical or magnetic injection.
The use of the spintronics requires that the materials used to fabricate the spin devices should possess the following requirements to be satisfied by the material:
- Efficient electrical injection of spin – polarized carriers.
- Efficient transmission during transport of carriers through semiconductor.
- Capability to detect or collect spin – polarized current.
The basic materials used in spin devices for manipulation of spin of electrons are the ferromagnetic which have the capability to change the spin polarization on application of magnetic fields.
The spin materials can be classified into two groups:
- Ferromagnetic Semiconductors
- Half-Magnetic ferromagnets
These are the materials with complete control over the spin electron. The main advantages of these types of materials are:
- Combined semiconducting and magnetic properties for multiple functionalities
- Easy growth of ferromagnetic-semiconductor nanostructures.
- Easy spin injection
As name suggests the half – magnetic ferromagnets doesn’t have full control over spin of the electrons.
The spin materials can be obtained as:
Substitution of V, Cr and Mn into GaAs, InAs, GaSb, GaP and INP.
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