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Questions and Answers
What is one significant disadvantage of high magnetic field equipment?
What is one significant disadvantage of high magnetic field equipment?
Which organization set a world record for achieving a magnetic field of 91.4 Tesla?
Which organization set a world record for achieving a magnetic field of 91.4 Tesla?
What does the Evans method primarily measure?
What does the Evans method primarily measure?
How is susceptibility estimated using the Evans method?
How is susceptibility estimated using the Evans method?
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What was the strength of the magnetic field achieved at NHML, Florida, as recorded?
What was the strength of the magnetic field achieved at NHML, Florida, as recorded?
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What is the unit of magnetic field strength named after Carl Friedrich Gauss?
What is the unit of magnetic field strength named after Carl Friedrich Gauss?
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What is the name of the measurement technique that employs a force exerted on a sample in an inhomogeneous magnetic field to determine magnetic susceptibility?
What is the name of the measurement technique that employs a force exerted on a sample in an inhomogeneous magnetic field to determine magnetic susceptibility?
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What is the relationship between the molar magnetic susceptibility, m, and the gram magnetic susceptibility, g, of a material?
What is the relationship between the molar magnetic susceptibility, m, and the gram magnetic susceptibility, g, of a material?
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In the Gouy method, which of the following factors can affect the accuracy of the obtained magnetic susceptibility value?
In the Gouy method, which of the following factors can affect the accuracy of the obtained magnetic susceptibility value?
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When measuring magnetic susceptibility using the Gouy method, which of the following represents the change in weight of the sample when it is placed in a magnetic field?
When measuring magnetic susceptibility using the Gouy method, which of the following represents the change in weight of the sample when it is placed in a magnetic field?
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What is the relationship between the magnetic susceptibility () of a material and its temperature (T) when the effective magnetic moment (so) is constant?
What is the relationship between the magnetic susceptibility () of a material and its temperature (T) when the effective magnetic moment (so) is constant?
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Which of the following is NOT a commonly used technique for measuring magnetic susceptibility?
Which of the following is NOT a commonly used technique for measuring magnetic susceptibility?
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Why is it important to measure the magnetic susceptibility of materials?
Why is it important to measure the magnetic susceptibility of materials?
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Which of the following techniques relies on the principle that a time-varying magnetic flux causes a current to flow in a closed circuit?
Which of the following techniques relies on the principle that a time-varying magnetic flux causes a current to flow in a closed circuit?
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Which of these techniques is best suited for measuring the magnetic properties of highly magnetic materials, even with small sample sizes?
Which of these techniques is best suited for measuring the magnetic properties of highly magnetic materials, even with small sample sizes?
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In the context of magnetic measurements, what is the significance of the induced voltage measured in a sensing coil, as described in the text?
In the context of magnetic measurements, what is the significance of the induced voltage measured in a sensing coil, as described in the text?
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Which of these is NOT a significant advantage of using a SQUID magnetometer for magnetic measurements?
Which of these is NOT a significant advantage of using a SQUID magnetometer for magnetic measurements?
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The SQUID magnetometer uses a superconducting (Sc) electromagnet to generate the magnetizing field. What is the primary advantage of using a superconducting electromagnet?
The SQUID magnetometer uses a superconducting (Sc) electromagnet to generate the magnetizing field. What is the primary advantage of using a superconducting electromagnet?
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What is the primary role of the second superconducting (Sc) loop in the SQUID magnetometer?
What is the primary role of the second superconducting (Sc) loop in the SQUID magnetometer?
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In the context of the techniques described, which method is most suitable for measuring the magnetic susceptibility of a solution?
In the context of the techniques described, which method is most suitable for measuring the magnetic susceptibility of a solution?
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Why does the VSM method have a limitation in terms of the sample size it can handle?
Why does the VSM method have a limitation in terms of the sample size it can handle?
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Flashcards
High Magnetic Field Record
High Magnetic Field Record
A record set for magnetic fields, with a peak of 91.4 Tesla achieved in June 2011.
Evans Method
Evans Method
A technique for measuring liquid samples' NMR, based on the presence of paramagnetic species.
NMR Chemical Shift
NMR Chemical Shift
The difference in frequency of resonances in NMR due to the presence of paramagnetic impurities.
Paramagnetic Species
Paramagnetic Species
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Magnetic Susceptibility
Magnetic Susceptibility
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Induction Methods
Induction Methods
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Vibrating-Sample Magnetometer (VSM)
Vibrating-Sample Magnetometer (VSM)
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Induced Voltage
Induced Voltage
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SQUID Magnetometer
SQUID Magnetometer
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Faraday’s Law
Faraday’s Law
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Gradiometer
Gradiometer
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Sensitivity in Magnetometry
Sensitivity in Magnetometry
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Applications of SQUID
Applications of SQUID
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Boltzmann constant (k)
Boltzmann constant (k)
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Bohr Magneton (β)
Bohr Magneton (β)
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Avogadro’s number (N)
Avogadro’s number (N)
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Magnetic field strength (H)
Magnetic field strength (H)
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Magnetic susceptibility (χ)
Magnetic susceptibility (χ)
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Gouy Method
Gouy Method
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Molar magnetic moment (M)
Molar magnetic moment (M)
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Gram magnetic susceptibility (χg)
Gram magnetic susceptibility (χg)
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Study Notes
Course Information
- Course Title: "CHM629" Magnetochemistry
- Course Description: Magnetochemistry of Inorganic compounds
- Instructor: Dr. Kuduva R. Vignesh
- Email: [email protected]
Lecture Delivery
- Delivery Method: Offline
Grades Evaluation
- Quiz/Debate/Assignments: 20%
- Mid-Semester Exams (two): 30%
- Final Exam: 50%
- Attendance Requirement: 50% to write the final exam
Magnetic Properties of Coordination Complexes
- Topics:
- Introduction & short history
- Definition & Units
- Experimental Measurement of χ, M
- Classes of Magnetism
- Temperature dependence of χ
- Van Vleck equation
- Magnetic anisotropy (g, ZFS)
- Single ion magnetic properties of coordination complexes
- Spin-crossover phenomena in coordination complexes
- Magnetic properties of di- and polynuclear complexes (SMMS, SMTs)
- Importance of calculations
- Magnetic data analysis
Historical Background
- First mention of magnetism: 625 B.C. (magnetite)
- Name "magnetism" from a Greek location with magnetic ore.
- Oldest directional tool: Iron spoon from China (280 BC)
Quantitative Treatment
- Exchange Hamiltonian by Heisenberg, Dirac, and Van Vleck
- Theory of anti-ferromagnetism (Ne'el 1932)
- Theory of ferromagnetism (Slater 1937)
- Theory of super-exchange (Anderson 1951)
Hard and Soft Magnets and Magnetic Flux
- Einstein quote about compass as a child.
Why Study Magnetism & Magnetic Materials?
- Ubiquitous in daily life
- Multi-billion dollar industry
- Medical applications (e.g., MRI agents)
- Telecommunications/IT (e.g., magnetic data storage)
- Motors, generators, etc.
- Intellectual Significance (molecular and solid-state chemistry and physics)
- Human biology and animal biology
- Magnetochemistry provides chemical and physical information
Noble Prize for Physics in 2007
- Discovery of Giant-Magneto-Resistance (GMR)
- Direct application to information storage devices
- 1988 discovery of GMR
- 1996 IBM launches GMR heads
- High sensitivity to read tiny memory elements
GMR Technology
- Translation of "La magnétorésistance géante" (Giant Magneto Resistance)
Molecular Magnetism
- Discusses carbon-based and metal-cluster-based molecular magnetism.
Definitions and Units
- Magnetochemistry: Use of magnetic techniques for structural information on simple paramagnetic systems. Uses physical measurements. (Carlin 1986)
- Molecular Magnetism: Interdisciplinary field where chemists design/synthesize materials with feedback from physicists who develop sophisticated experimental measurements to model their properties. (Kahn 1993)
Current Magnetic Materials in Industrial Use
- Non-molecular (e.g., magnetite, CrO2, Fe, Ni, Co)
- d- or f-orbital (transition/lanthanide) based spin-sites
- Extended network bonding in 2- or 3-dimensions
- Prepared by high-temperature metallurgical processes.
- Molecule-based magnets can offer specific alteration of magnetic properties, combination with mechanical/electrical/optical properties, simplicity of fabrication, "designer magnets", and new generations of magnetic/electronic/photonic devices
Spin Cross-Over
- The system "remembers" its thermal past
- Graph of XmT vs T
- Discussion of bistability domain and room temperature
LS-HS Transition: Applications (Display Device)
- Diagrams of thin layer compound in low spin state and display.
Origin of Magnetism
- The electron is the origin of magnetism
- Rest mass, charge and magnetic moment of the electron
Magnetic Susceptibility
- Definition and calculation
- x = dM/dH
- x = M/H (for weak fields)
Measurement of χ
- Force method: The Gouy method
- Sample placed in inhomogeneous magnetic field
- Displacement force
- Weight change
- Advantage: good sensitivity (~ 10-6 to 10-8 emu)
- Disadvantage: Requires large sample amount
- Induction method: The vibrating-sample magnetometer (VSM)
- Sample oscillates in uniform magnetic field
- Induced voltage in sensing coil ∝ χ
- Advantage: Robustness
- Disadvantage: Poor sensitivity (and only small samples can be used)
SQUID Magnetometer
- Superconducting Quantum Interference Device
- Faraday’s law: Time-varying magnetic flux causes current in closed circuit
- First and second-order gradiometer
- Used in most modern magnetochemical studies
- Sample is surrounded by superconducting sensing coil coupled to a second Sc loop
- Magnetized sample is moved through coil, inducing current
- SQUID amplifies small magnetic field changes into large electrical signals
- Advantages: Very sensitive (> 10-12 emu); Can study single-crystal samples, powders, Easy temperature control
- Disadvantages: Complex and expensive equipment
Evans Method (Liquid Samples)
- Measuring magnetic susceptibility for liquid samples using NMR chemical shift differences in different solvents presence of paramagnetic species
- Small capillary with solution in water (e.g.) and indicator (e.g., tert-butyl-alcohol) in an NMR tube
- Resonance position of a line in NMR spectrum depends on bulk magnetic susceptibility
- Susceptibility estimate from difference in Hz values between signals
Magnetic Susceptibility (Detailed)
- Molar susceptibility xM (cm³/mol)
- Shift in frequency δν (Hz)
- Molecular mass M, (g/cm³)
- Solute concentration (g/cm³)
- Shape factor Sf of the magnet
- Diamagnetic correction
Common Experimental Protocols
- Zero-Field-Cooled (ZFC) Measurements
- Cools to 2K, applies magnetic field and heats to 300K for ZFC
- Use to freeze random contributions of the sample
- Gives temp. Dependence of susceptibility
- Field-Cooled (FC) Measurements
- Cools to 2K with an applied magnetic field
- Has blocking/freezing temperature TB
- Field scan
- Field is swept at low temp. (Hysteresis area)
- Eq valid for small H/kT
- Above a field, saturation occurs, which gives unpaired electrons
- Reduced Magnetization
- M vs H/T (different temperatures)
- Zero-field splitting
Hysteresis
- Studying hysteresis loops
AC Susceptibility Measurement
- Setup: First-order gradient coil inside primary coil that induces alternating magnetic field
- Investigating magnetization dynamics by varying frequency
- Measuring adiabatic (high frequency) or isothermal (low frequency) susceptibility
Classes of Magnetism
- Diamagnetism: Negative susceptibility, paired electrons
- Paramagnetism: Positive susceptibility, unpaired electrons.
Molecules
- Dihydrogen (diamagnetic, Spin S = 0)
- Dinitrogen (diamagnetic, Spin S = 0)
Dioxygen
- Paramagnetic (spin S = 1), when in its ground state
- Reactivity is weak in its ground state.
Examples of Paramagnetic species
- Nitrogen Monoxide (NO)
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Description
Test your understanding of the magnetic properties of coordination complexes as covered in CHM629. This quiz will explore key topics including the history of magnetochemistry, types of magnetism, and the analysis of magnetic data. Prepare to deepen your knowledge on complex magnetic behaviors and measurements.
