Introduction to the Vibrating sample magnetometer and thermogravimetric & differential thermal analyser

1. Analysis of VSM and
TG/DTA
Antilen Jacob G
Research Scholar

2. Fig. a)
Fig. b)
• Types of Magnetism- dia, para, ferro, ferri, antiferro
• spontaneous magnetization & magnetic ordering temperature
• Hysteresis – VSM - Characterize the magnetization of
materials
Introduction
Fig. c) Fig. d) Fig. e) http://www.irm.umn.edu/

3. Hysteresis loop
• The section of the major hysteresis loop from
negative saturation to positive saturation is called
the ascending major curve
• The largest achievable magnetization is called the
saturation magnetization
• The magnetic field at the magnetization is zero is
called the coercivity (Hc)
• magnetization whenever the applied field is zero
is called the remanence ( Mrem)
• The slope of loop is called the susceptibility
• Change in field direction during ascending or
descending major loop called turning points and
such traversals are called first-order reversal
curves
Giorgio Bertotti (Hysteresis in magnetism)

4. Hard and Soft magnetic materials
• If a small applied field suffices to
produce saturation, the material is
said to be magnetically soft
Cullity, magnetism book

5. Pinning and nucleation
• Pinning sites hinders the
domain walls to move
• nucleation sites will promote
easy movement of domain
walls
Google images

6. Magnetic Anisotropy
• Strongly affect the shape of the M, H (or B, H)
curve is magnetic anisotropy
• Crystal anisotropy, formally called magneto
crystalline anisotropy, Shape anisotropy, Stress
anisotropy, magnetic induced anisotropy and
Exchange anisotropy
• In nickel the direction of easy magnetization is
<111> and also for all the cubic ferrites
• Thin film and crystals
Prakash et al.,
440 Oe
148 Oe

7. Stress and crystal lattice defects
Effect of structural deformation
Ni
Tension force was parallel to H Tension force right angled to H
Effect of stress and strain
https://www.tf.uni-kiel.de/

8. Size dependent coercivity
Superparamagnetic

9. 𝜒 values for different magnetic materials
Fig. a) Fig. b) Fig. c)
Fig. d) Fig. e)
• Diamagnetic (-10)
• paramagnetic (+1)
• superparamagnetic (+5000)
• ferromagnetic ( > 10000)

10. FORC
• Calculate a distribution of coercive and
interaction fields of the fundamental hysteretic
entities
• The FORC diagram is the contour plot
representation of the distribution function using
the coercive field axis and the interaction field axis
Roberts et al.,
Non- Interacting SD Interacting SD

11. Size effect in FORC analysis
Monika Kumari et al., JAP
• An increase in the
contribution from
SD particles is seen
by the increase in
the spread along Hc
axis

12. Thermogravimetric analysis (TGA)
• TGA is an experimental technique in which the
mass of a sample is measured as a function of
sample temperature or as a function of the time
in isothermal experiments
• A number of different effects can cause a sample
to lose, or even gain, mass and so produce steps
in the TGA curve
• Evaporation of volatile constituents, Oxidation,
Oxidative decomposition of organic substances,
Thermal decomposition, Heterogeneous chemical
reactions, Ferromagnetic materials.

13. TGA Components
Null- balance principle

14. Design and Measuring Principle
Buoyancy Correction
• Balances are classed as semi micro - (10 μg), micro- (1 μg)
or ultra micro - (0.1 μg) balances.
• Besides resolution, the (continuously measurable)
maximum capacity of the balance is also an important
factor
• Protection of balances
• Due to the change in density of a gas as the temperature
changes, buoyancy corrections must be made in TGA
measurements
• Buoyancy correction is essential for tests such as ash
content where the residue at the end of the test needs to be
determined accurately
• the buoyancy effect is corrected by subtracting a blank
curve from the measurement curve
𝐹 = 𝑉. 𝜌. 𝑔 --------------------(1)
where, F is the up thrust or buoyancy
V is immersed medium
g is acceleration due to gravity
𝑚 = 𝑉. 𝜌 -----------------------(2)
The temperature dependence of density
𝜌 = 𝜌𝑜
𝑇𝑜
𝑇
𝜌𝑜 is the density of gas at the reference temperature 𝑇𝑜

15. TGA Basics
A – No mass change
B – Desorption
C- Single stage decomposition
D – Multi stage decomposition
E – Multi stage decomposition
F – Oxidative reaction
G – Oxidative reaction followed with decomposition
1st Step CaC2O4 • H2O (s) CaC2O4 (s) + H2O (g)
2nd Step CaC2O4 (s) CaCO3 (s) + CO (g)
3rd Step CaCO3 (s) CaO(s) + CO2
Decomposing of calcium
oxalate monohydrate

16. Factors affecting TGA curve
• Pan material type
• Ramp rate
• Purge gas
• Sample mass
(a)
(b)
(c) (d)
a) 10 mg samples of PTFE, heated at
2.5, 5, 10 and 20 °C/min b)
Reinforced polypropylene c)
Polystyrene d) calcium oxalate

17. DTA Measurement Principle
Block furnace Boersma DTA
SDTA (Single DTA)
• In addition to showing the energetic nature of
events involving mass loss, the DTA signal can
also show thermal effects that are not
accompanied by a change in mass, for example
melting, crystallization, or a glass transition
• The evaluation is usually restricted to the
determination of onset and peak temperatures

18. The Calculation of the DSC Curve from DTA
• DTA curves show that the areas of
melting peaks are proportional to the
sample mass used and are therefore
proportional to the amount of heat
exchanged.
• The calibration curve is obtained by
means of so-called calibration factors, k,
which are plotted against the
corresponding temperatures
• If the enthalpy of fusion, Δhfus, of the
reference substance used is known, the
calibration factor, k, of the enthalpy of
melting to the peak area, Apeak, can be
calculated according to the equation
𝑘 =
𝑚∆ℎ𝑓𝑢𝑠
𝐴𝑝𝑒𝑎𝑘
The figure shows TGA and SDTA measurements of copper sulfate pentahydrate. The SDTA
curve is multiplied by the k curve to obtain the DSC curve. This can be integrated just like
a directly measured DSC curve to obtain enthalpy changes.