Exchange interaction of soft and hard magnetic phases in exchange- Spring magnet of Nd3Tb1 Fe76Cu0•5Nb1 B18.5. has been accepted as satisfactory in partial fulfillment for the degree of Master of Philosophy in Physics and it is certified that the student has demonstrated satisfactory knowledge in the field covered by this thesis in an oral examination held on December 18, 2010. It is hereby declared that this thesis or any part thereof has not been submitted elsewhere for the award of any degree or diploma.
A LIST OF SYMBOLS
Abdul Hakim, Chief Engineer and I-lead, Materials Science Division, Atomic Energy Centre, Dhaka, for his generous support in carrying out my work. I would like to express my gratitude to all my valued teachers at Department of Physics ol Govt.
ABSTRACT
Nd - Deficient Nd2Fe14B/1c3B based nanocomposite alloys are characterized by their source exchange behavior resulting in remanence ratio greater than 0.5, which is highly desirable for permanent magnetic materials. In addition to high reduced remanence, such systems possess high energy output (BI I) and a reversible demagnetization curve, which has been termed source-exchange behavior.
CHAPTER -1 INTRODUCTION
In Fe-based soft nanocomposite magnetic materials, the temperature dependence of permeability is determined by the composition of the remaining amorphous and nanostructured phases. When the sample is annealed too much, overaging of the nanograins would cause the demagnetization curve to become concave.
CHAPTER -2
SOFT AND HARD EXCHANGE-BIASED SYSTEM
SOFT AND HARD EXCHANGE-BIASED SYSTEM
Introduction
Therefore, the maximum energy product is a basic parameter for measuring the performance of the permanent magnets. Kncllcr and Hawig 2' used a one-dimensional model shown in Figure 2.1 to represent the basic principles of the exchange coupling between the hard magnetic phase (k phase) and the soft magnetic phase (m phase).
Effect of Exchange Coupling on the Macro-Magnetic Properties V.ssentlal conditions Ir the iii icrustructute of such materials are alline and regular
- Volume Fractions of Phases
- Effect of Rernanence Enhancement
- Effect of Coercivity Red uction
- Effect of Exchange Coupling on the Demagnetizing Curve
- Spring - Magnet Behavior
- Saturation Rernanence Ratio
- Nucleation Field and Coercive Field
The grain size of the soft magnetic phase should be twice the domain wall width of the hard magnetic phase. 17 originating from the union of exchange can only be rcachcd at the expense of cokrvity.
Magnetic Properties in the Optimum State
Analysis of the total magnetization change. ii)— (ii), along the demagnetization curve M (1-1), after previous saturation in the opposite direction in the retained H = 1200 kAlm of the alloy in the optimal magnetic state. a) Measurements of the irreversible part. Therefore, most of the distribution f(I-I1) is due to the distribution of the angles 0, while the mechanism of the irreversible magnetization reversal and the k and m phases involved are the same throughout the sample.
GKUE7
The initial (below the maximum) and final (high 1-I) parts of the curve in combination with shown in figure. The most remarkable feature of the curve is the sharp maximum at H=I-I, i.e. exactly where it should be. expected due to the proposed magnetization mechanism. Figure 2.7 shows the coercivity lli of the alloy in the optimal state as a function of temperature T.
As we can see, the cxtra cocricivity obtained by the exchange coupling of the sofl rn phase to the hard k phase decreases with increasing 'I' and disappears at the Curie temperature of the hard phase Nd2 Fc1 .1B (Tk = 580 K, see table 2.1). The end of the steep decrease in HM(T) corresponds to the Curie temperature of the hard phase Nd2 Fii13,Te = 580 K.
CHAPTER -3
AN OVERVIEW OF NANOCRYSTALLINE MATERIALS
- An Overview of Nanocrystalline Materials
- History of amorphous and nanocrystallinc materials
- Kinds of nanocrystaltine alloys
- Fe-based Soft Nanocomposite Magnetic Material
- Formation of NanocrystaHine State
- Conditions for the formation of NanocrystaHine aHoys
- Grain Size and Coercive force of Nanocrystalline alloys
Nanocrystalline materials represent one of the most active fields of research in recent times for the atomic adaptation of materials with specific properties and combinations of properties. It has been proven that the controlled crystallization of amorphous alloys in the form of their ribbons prepared by the rapid solidification technique using melt spinning appears to be the most suitable method available so far to synthesize nanocrystalline alloys with attractive magnetic properties . Fig.3.2 Schematic illustration of the formation of nanocrystalline structure in Fe-Cu-Nb-Si-B alloys.
In the initial stages of the anucalin, Cu-rich clusters are brined by either a spinodal process or nucleation in the amorphous state. Identification of good characterization methods, where the nanometer size range of these materials falls just below or at the resolution limit of the conventional tools.
FINEMET'
- Various Kin(Is of Energies in the I'orrnation of Magnetic Domains
- Magnetostatic Energy
- Magnetostrictive Energy
- Anisotropy energy
- Zeeman Energy
- Magnetization and Magnetic Induction
Domains are formed primarily to reduce magnetostatic energy, which is the magnetic potential energy contained in the field lines connecting the north and south poles outside the material. Lowerevcr, since E also includes Ek, it is not necessary to include E as a separate term in cqu. This energy is due to niagnetostriction flow, a slight change in the dimensions of the crystal when it is magnetized.
This causes elastic stresses in the lattice and the direction of magnetization that minimizes these strain energies will be affected. So the magnetization is also the pole strength per unit area in A.m units, which is equivalent to 1 O gauss ((1) in the CUS system.
- Susceptibility and Permeability
- Theory of Permeability
- Coercivity
- Various Kinds of Magnetism
- Origin of Magnetism (Quantum Mechanical View)
- Magnetism of the Electron
It is now known that the magnetic behavior of atoms, molecules and solids is related to the orbital and rotational motion of negatively charged electrons. In the simplest case, (ie for the hydrogen atom) the motion of the electron is governed by three quantum numbers (i) the principal quantum number ,n, where ii = 1,2,3. The left side of equation (1 .5.3) represents the ratio of the magnetic moment vector in terms of Bohr magnetons to the orbital angular momentum vector in terms of 'Ii.
Orbital angular momentum is derived from the rotational motion of the electron around the nucleus in a simple Bohr model. It is similar in the case of d and d, orbital. iii) For a high spin d configuration, the orbital angular momentum will be relaxed because all the orbitals will contain electrons of the same spin.
CHAPTER -4
PREPARATION OF NANOCRYSTALLINE ALLOY
- Preparation of Nanocrystalline AHoy
- Methods used for Preparation of Nanocrystalline AHoy
- The Fast Cooling of the Melt
- Sample Preparation .1 Master alloy Preparation
- Preparation of ribbon by Melt Spinning Technique
- Important Factors to Control the Thickness of Ribbons
- Confirmation of Amorphousity of Ribbons
- X-ray Powder Method
- Experimental Technique for X-ray Diffractometer
- Analysis of XRD Data
In this thesis work, amorphous bands have been produced by rapid cooling of mcli. The temperature was monitored by an external pyrometer from the upper surface of the molten alloy through a quartz window. From the XRD pattern of the tape sample, no peaks are observed within the scan area.
Thus, from the overall X-ray diffraction pattern, it is confirmed that both samples are in an amorphous state. The interplanner distance d was calculated from these 20 values of the diffraction peaks using Bragg's law (in Figure 4.3).
1) Identification of Phases
Usually, the lattice parameter of the alloy composition is determined by the Dchye-Scherrer method after curve extrapolation. The main objective (life point) of this study is to determine the nanocrystalline grain size for all heat-treated alloy composition samples using the Scherrer method. The XRD reflection pattern (i 1 o) for different heat treatment temperature steps of the alloy composition is used to calculate the grain size.
All grain size values were determined for each level of heat treatment temperature of the alloy composition. The peak FWI-IM is large at the early heat treatment temperature, and as the heat treatment temperature increases, the FWI-IM value becomes smaller, which means that the grain size gradually increases.
Thermal Treatment of the Amorphous Ribbon
For their purpose, a laboratory-built vacuum system made of quartz tube capable of being rated up to torr was used. The samples were placed in a quartz tube and evaluated (10'torr) before being placed in a plate furnace heated to the current temperature and kept for as long as necessary to complete annealing.
SQUID Magnetometers
- Superconducting Magnet
- SQUID
- Sn percond ucting Magnetic Shield
- Applications
- Improved Sensitivity
- Extended Temperature Capability
This pickup coil system is placed in the uniform magnetic field region of the solenoidal superconducting magnet. Consequently, the magnetic moment of the sample induces an electric current in the pickup coil system. A change in the magnetic flux in these coils changes the continuous current in the detection circuit.
So the change in current in the detection coils produces variation in the SQUID output voltage proportional to the magnetic moment olsample. The Maximuni Slope method oscillates the sample over a small range (2 mm) at the most linear part of the SQUID response (as shown in Fig.-4.IO).
EqP 1
- Enhanced Tlieruiometry a fl(I 'tern peratu re Sweep Operation
- Software Control / Automation
- Principle of Vibrating Sample Magnetometer
- Description and brief Working Principle of Hirst VSM02
- Working Principle of Vibrating Sample Magnetometer
In addition to a redesigned impedance system. The MPMS XL uses a new thermometer design for improved temperature accuracy and precise thermal control. This iiripiovcd design is combined with new temperature control capabilities to provide more accurate measurements of sam pie charn hers, even tinder extreme temperature changes. Magnetization is defined as the magnetic moment per unit volume or mass of the substance.
Vibrating sample magnetometers, as the name implies, vibrate the sample as part of the measurement process. This provides the flow meter element of the system with the dynamic component it requires to make the measurement.
76 same frequency of vibration and its amplitude will be proportional to the
Applications
Using a vibrating sample magnetometer, the direct current magnetic moment as a function of temperature can be measured. Some of the most common measurements are: hysteresis loops, sensitivity or saturation magnetization as a function of temperature (thermomagnetic analysis), CLIFVCS magnetization as a function of angle (anisotropy), and magnetization as a function of time.
CHAPTER- 5
RESULTS AND DISCUSSION
Results and Discussion
X-ray Diffraction (XRD) Analysis
- Effect of Differeni Annealing Time of Hysteresis Parameter of
Fig.- 5.2 X-ray diffraction patterns for samples annealed at 923 K for annealing time of 3 minutes. Fig.- 5.6 X-ray diffraction patterns for samples annealed at 923 K for annealing time of 1 minute. Fig.- 5.12 Comparison of hysteresis loops for samples annealed at 923 K for an annealing time of 5 minutes.
Figure- 5.14 shows the hysteresis loop at room temperature (300 K) and some smaller feedback loops along the demagnetization branch for a sample annealed at 923 K for 3 minutes. For the sample annealed at 923 K, the curve D(l 1) versus 1-I is characterized by a relatively sharp change in D(l-l) at the critical field where an irreversible change occurs in the hard phase, which was obtained 11Dm derivative D (ll) vs.
CHAPTER -6 CONCLUSIONS
1. 6.0 Conclusions
A study of the difficulty properties of some well-known materials of both categories in Table-S. Furthermore, the best of the k materials contain about 25 wt% or more of a rare earth metal, which increases their cost and raises serious problems of rcspcct for chemical stability, while most m materials are very reactive and quite cheap. Therefore, it is tempting to consider composite materials consisting of two suitably dispersed and interexchange-coupled phases, one of which is k-type, providing a high enough nucleation for irreversible magnetization reversal, and the other is an in-type material with M as high as possible to achieve a high average saturation.
Finally, it is shown how such a material can be technologically realized and that its magnetic behavior fully corresponds to the predictions of the theory. Recoil hysteresis loops are characterized by high recoil permeability and small recoil loop area, indicating that the samples are exchange-coupled.
34;Eilct of structural parameters on soft magnetic properties of two-phase nanocrystalline alloy of Fc73.5CumTa3Si1 3.5B9"; J. Van iamtu It., Matsuura Y.; Pernianent magnetic materials based on rare earth-ion-boron tetragonal trans compounds; IE .
NUCLEAR SCIENCE AND
APPLiCATIONS
EDITORIAL BOARD
Abdul Hakim Member-Secretary : Naznccn Ara Afsary
Bangladesh Atomic Energy Commission
