Study of Ferromagnetic Transition Temperature
and Superconductivity using PQMS
RAHUL SINGH (230502)
I-PhD (Physics)
Group-7
Oct 15, 2024
1 Aim
• Identification of Magnetic Transition Temperature using AC Susceptibility Measurements.
2 Apparatus Used
• PQMS Device(Physical Quantity Measurement System)
• Lock in Amplifier, Temperature Controller and Ultra Low Current Measuring Unit
• I-V Source and Measurement and Magnet Power Supply
3 Chemical Substance Used
• YBCO(Yittrium Barium Copper Oxide) and Gladolinium
• Liquid Nitrogen and Liquid Helium
4 Experimental Setup
Figure 1: XPLORE Physical Quantities Measurement System (PQMS)
1
• XPLORE PQMS is an easy-to-use, versatile system for acquiring experimental plots of magnetic
AC susceptibility and electrical resistance of your sample as a function of temperature.
5 Procedure
• Mount a sample on the chosen insert.(Variable Temperature Insert and High Resistivity Variable
Temperature Insert)
• Evacuate the sample and heater chambers.(Note: Ensure that all the valves are in the closed
position)
• Flush the chosen chamber with Helium.
• Cool the Cryostat with Liquid Nitrogen.
• Load an Insert into the Cryostat.
• Unload an Insert from the Cryostat.
6 Theory
6.1 Superconductivity
The complete disappearance of electrical resistance in various solids when they are cooled below a
characteristic temperature. This temperature, called the transition temperature, varies for different
materials.
• A conductor allows for the passage of a finite charge current I given an applied potential difference
V.
• An insulator resists a charge flow I = 0 for a large range of V .
• A superconductor on the other hand permits a finite current with no associated potential drop
V = 0.
Material I V
Conductor finite finite
Insulator 0 finite
Superconductor finite 0
6.2 High Temperature Superconductors
These are materials with critical temperature (the temperature below which the material behaves as
a superconductor) above 77 K, the boiling point of liquid nitrogen.
• They are only ”high-temperature” relative to previously known superconductors, which function
at even colder temperatures, close to absolute zero. These are still far below room temperature,
and therefore require cooling.
• HT superconductors can be cooled by Liquid Nitrogen, in contrast to LT superconductors which
require expensive and hard-to-handle coolants, primarily Liquid Helium.
• They retain their superconductivity in higher magnetic fields than previous materials.
• The majority of high-temperature superconductors are ceramic materials, rather than the previ-
ously known metallic materials.
2
6.3 Yttrium Barium Copper Oxide (YBCO)
The main class of high-temperature superconductors is copper oxides combined with other metals, es-
pecially the rare-earth barium copper oxides (REBCOs) such as yttrium barium copper oxide(YBCO).
• It is a family of crystalline chemical compounds that display high-temperature superconductivity
• It includes the first material ever discovered to become superconducting above the boiling point
of liquid nitrogen [77 K] at about 93 K.
• Many YBCO compounds have the general formula YBa2 Cu3 O7−x (also known as Y123).
• Optimum superconducting properties occur when x ∼ 0.07
• YBCO crystallizes in a defect perovskite structure consisting of layers.
• The boundary of each layer is defined by planes of square planar CuO4 units sharing 4 vertices.
Perpendicular to these CuO4 planes are CuO2 ribbons sharing 2 vertices.
• The yttrium atoms are found between the CuO4 planes, while the barium atoms are found
between the CuO2 ribbons and the CuO4 planes.
In this experiment, we study the ac susceptibility vs temperature characteristics of a high-temperature
superconductor YBCO. From the data obtained, we determine the critical temperature at which the
transition from normal to superconducting state occurs.
6.4 Gadolinium
Gadolinium is a chemical element; it has symbol Gd and atomic number 64. It is the eighth member
of the lanthanide series. Gadolinium is believed to be ferromagnetic at temperatures below 20 °C (68
°F) and is strongly paramagnetic above this temperature.
6.5 AC Susceptibility
AC susceptibility is a technique used in the study of magnetic materials to measure how a material
responds to an alternating current (AC) magnetic field.
• Magnetic susceptibility is a measure of how much a material will become magnetized in response
to an applied magnetic field. It is defined as the ratio of the induced magnetization M to the
applied magnetic field H.
M
χ=
H
For AC susceptibility, this is measured under an oscillating magnetic field.
• In AC susceptibility measurements, the applied magnetic field oscillates with a certain frequency
ω (angular frequency), typically in the range of a few Hertz to several kilohertz.
• AC susceptibility is the standard tool for determining the physics of superconductors, in partic-
ular for measuring critical temperature, by observing changes in χ as the material transitions
from a normal state to a superconducting state.
• In the normal state (above the critical temperature), superconductors typically have a small
susceptibility. In the fully superconducting state, the sample is a perfect diamagnet.
3
6.6 Pirani Gauge
The Pirani Gauge is a type of Thermal Conductivity Gauge used for the measurement of the pressures
in vacuum systems. The Pirani gauge consists of a metal sensor wire (usually gold plated tungsten or
platinum) suspended in a tube which is connected to the system whose vacuum is to be measured. The
wire is usually coiled to make the gauge more compact. The sensor wire is connected to an electrical
circuit from which, after calibration, a pressure reading may be taken.
Principle : A heated metal wire (sensor wire, or simply sensor) suspended in a gas will lose
heat to the gas as its molecules collide with the wire and remove heat. If the gas pressure is reduced,
the number of molecules present will fall proportionately and the wire will lose heat more slowly.
Measuring the heat loss (filament’s cooling rate) is an indirect indication of pressure.
6.7 Cryostat
A cryostat is a device used to maintain low cryogenic temperatures of samples or devices mounted
within the cryostat. Low temperatures may be maintained within a cryostat by using various refriger-
ation methods, most commonly using cryogenic fluid bath such as liquid helium, liquid nitrogen, etc.
In our experiment there are 3 chambers in the cryostat : Sample chamber, Heating chamber,
and Outer chamber. In the sampling chamber, there is a primary solenoid, and beside it, there are
two secondary solenoids in opposite polarity, wherein our sample will be moving.
6.8 Magnetic AC-susceptibility measurement
The sample is placed inside an air core solenoid (primary coil) and excited with a sinusoidal magnetic
field. When the sample is subjected to the sinusoidal magnetic field, its magnetic properties (i.e.,
magnetization) change over time in response to this field. The resulting time varying magnetization
is sensed using a pair of coaxial and symmetrical pick-up coils (secondary coils) wounded in opposite
directions giving us two positions for extreme susceptibilities. The sensed signal from the pick-up
coil is fed back to the lock-in amplifier with an in-built reference generator for demodulation. Both
amplitude and phase of the sensed signal are recorded to produce in-phase (χ′ ) and quadrature-phase
(χ′′ ) measurements.
7 Observation
Figure 2: χ-L for Gadolinium
4
Figure 3: χ-T for Gadolinium
Figure 4: χ-L for YBCO
5
Figure 5: χ-T for YBCO
8 Result
8.1 Gadolinium
• Extreme Susceptibilities: 85.7 × 10−5 a.u (max) and −75.5 × 10−5 a.u (min)
• Extreme Susceptibility Probe Positions: 0.028 (mm) and 0.048 (mm)
• Magnetic Transition Temperature: ∼ 289 K
8.2 YBCO
• Extreme Susceptibilities: 8.116203 × 10−5 a.u (max) and 1.500496 × 10−5 a.u (min)
• Extreme Susceptibility Probe Positions: 0.029 (mm) and 0.048 (mm)
• Magnetic Transition Temperature: ∼ 95.8 K
9 Precautions
1. While purging ensure that helium knob is turned atmost for two seconds.
2. Ensure that the vaccum is until 0.02 mbar before starting the experiment.
3. Be careful while handling liquid Nitrogen.
4. To keep the cryostat protected from dust and moisture, always cover the cryostat’s opening using
an insert or its cover, fastening it firmly in place with a clamp.
5. Always evacuate the sample and heater chamber when the system is not in use! This reduces
the accumulation of moisture and dust inside the cryostat.
6. Prior to flushing any chamber, ensure that an insert/cover is in place over the cryostat’s orifice
and is securely fastened by a clamp.
7. Flushing helium while loading/unloading an insert prevents the condensation of atmospheric
water vapour inside the cryostat. Moisture causes damage to the cryostat.
