Funtional properties

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Doubts

1. why does diamagnetic field dominate in the hysterisis curve during high magnetic field?

2. What is a magnon

Reminder

1. Read up on the different exchange energy.

2. Read up on quantum hall effect

3. Read pg 29/30

- PG 14/8, 9/8

4. COULD read more about mossbaer spectroscopy.

5. photoelectric effect an blackbody radiation

6. read on density of states

7. how is kronig penney model able to explain the energy band gaps

NOTES

When external field is applied to the multi-domain ferromagnet, saturation magnetization can be

achieved through the domain wall motion, which is energetically inexpensive, rather than

through magnetization rotation, which carries large anisotropy energy penalty.

Some of the key magnetic devices found in advanced electronics like computers and MP3 players utilize an effect called “exchange bias” to pin (i.e. fix) the magnetization M of a ferromagnetic (FM) reference layer in a fixed direction in space. Relative to the fixed direction of M in the reference layer, o ne may then align the magnetization direction of a second ferromagnetic layer, called the sensor layer at an arbitrary angle. If the direction of M in the sensor layer is rotated by a magnetic field, the device acts as a sensor for the direction and strength of the magnetic field through the giant magnetoresistance effect, as utilized in magnetic recording heads and shown on the left of Fig. 1. If M in the sensor layer is used to define two distinct states, either parallel or antiparallel to the reference layer, we have a memory cell consisting of “1” and “0” bits, as shown on the right of Fig. 1. The key requir ement is to keep the reference layer unaffected by whatever one does with the sensor layer – and this is assured by exchange bias. In general, the effect is defined as the unidirectional pinning of a ferromagnetic layer by an adjacent antiferromagnet (AFM). For many years the ex change bias effect, discovered in 1956 by Meiklejohn and Bean, has been optimized through materials engineering and employed in devices without a good scientific understanding.

VSM measures the magnetization of a small sample of magnetic material placed in an external magnetizing field by converting the dipole field of the sample into an AC electrical signal. VSM measures the magnetization of a small sample of magnetic material placed in an external magnetizing field by converting the dipole field of the sample into an AC electrical signal.

Where the modulated gamma-ray energy matches precisely the energy of a nuclear transition in the absorber the gamma-rays are resonantly absorbed and we see a peak