Description
We offer Magnetoresistance set-up, it is noticed that the
resistance of the sample changes when the magnetic field is turned
on. The phenomenon, called magnetoresistance, is due to the fact
that the drift velocity of all carriers is not same. With the
magnetic field on; the Hall voltage V = Eyt = v X H compensates
exactly the Lorentz force for carriers with the average velocity;
slower carriers will be over compensated and faster one
undercompensated, resulting in trajectories that are not along the
applied field. This results in an effective decrease of the mean
free path and hence an increase in resistivity.
Here the above referred symbols are defines as: v = drift
velocity; E = applied electric field; t = thickness of the crystal;
H = Magnetic field.
The set-up consists of the following:
(1) Four Probe arrangement, MRA**1
It consists of 4 collinear, equally spaced (2mm) and individually
spring loaded probes mounted on a PCB strip. Two outer probes for
supplying the constant current to the sample and two inner probes
for measuring the voltage developed across these probes. This
eliminates the error due to contact resistance which is
particularly serious in semiconductors. A platform is also provided
for placing the sample and mounting the Four Probes on It.
(2) Sample
Ge Crystal (n-type) dimensions: *0 x *0 x 0.5mm.
(3) Magnetoresistance Set-up, Model DMR**1
This unit consists of a digital millivoltmeter and constant current
power supply. The voltage and probe current can be read on the same
digital panel meter through a selector switch.
(a) Digital Millivoltmeter
Intersil 3½ digit single chip ICL ***7 have been used. Since the
use of internal reference causes the degradation in performance due
to internal heating an external reference have been used. Digital
voltmeter is much more convenient to use, because the input voltage
of either polarity can be measured.
Specifications
Range : ****0mV (**0μV minimum)
Accuracy : ±0.1% of reading ± 1 digit
(b) Constant Current Power Supply
This power supply, specially designed for Hall Probe, provides **0%
protection against crystal burn-out due to excessive current. The
supply is a highly regulated and practically ripple free dc
source.
Specifications
Current : ***0mA Resolution : *0μA
Accuracy : ±0.2% of the reading ±1 digit
Load regulated : 0.*3% for 0 to full load
Line regulation : 0.*5% for *0% variation
(4) Electromagnet, EMU**0V
(5) Constant Current Power Supply, DPS**0
(6) Digital Gaussmeter, DGM***2/DGM***2
The Set-up complete in all respect.
