Biodegradable mems. Vocabbox. A lot of machines made by physicists are used in medicine now, страница 14

In the second study Frithjof Nolting of the Lawrence Berkeley National Laboratory and co-workers from the US and Switzerland used polarized X-rays to study the spins at a magnetic interface. The X-rays interact with the magnetic moment of the atoms and can thus be used to image the magnetic domains. If the X-ray wavelength can be tuned, as it can in a synchrotron, the radiation can also be used to selectively image a single element. The Swiss-US team used this combination of techniques, known as X-ray magnetic dichroism spectromicroscopy, to selectively image the magnetic orientation of a layer of ferromagnetic cobalt on top of an antiferromagnetic film of lanthanum iron oxide.

At 20 nm, the spatial resolution is short enough to resolve the relative orientation of the antiferromagnetic and ferromagnetic domains. The results show that the spins of the ferromagnetic atoms are aligned parallel or antiparallel to those of the antiferromagnet. This relative orientation gives rise to a local exchange bias even though there is no such bias for the material as a whole in the absence of a magnetic field.

The latest research shows that a number of complementary techniques can now be used to image the magnetic structure of interesting materials at nanometre scales. It will not be long before we can make detailed experimental measurements that will constrain theoretical models. Theorists beware.

Comprehension check

1.  Write a brief summary of each part.

2.  Do the translation of the most difficult sentences or parts of the text.

3.  Make up your own vocabulary on this text so that to use it in discussion on the topic.

Discussion

1.  Speak on the factors that motivated an incredible rise of the interest in the field of magnetism.

2.  Characterise the properties of a ferromagnet and an antiferromagnet.

3.  Analyse three major ways to image magnetic materials at the atomic level.

4.  Discuss future possible trends in basic and applied research of magnetism.

UNIT 2

COLLOIDS  REINFORCE  GLASS  THEORY

Vocabbox

noun collocations

§  glass transition

§  solid state physics

§  periodic arrays

§  sluggish motion

§  string-like paths

§  confocal optical microscopy

verb collocations

§  confirm

§  obey the rules

§  focus to different depths

§  observe

§  approach

§  restrict

§  establish

Pre-reading task

Before you read name the main problems that you think are touched upon in this text.

Reading

Read the text. Divide it into logical parts. What is the main thought of each part?

In 1995 Philip Anderson wrote that the glass transition remains the deepest and most important unsolved problem in solid-state physics. Why is there so much mystery surrounding the seemingly simple solidification of a liquid into a disordered solid, like glass - one of the most ubiquitous forms of matter?

Part of the mystery lies in the dramatic slowing down of molecular motion that accompanies glass formation. Molecules in the liquid can move 10¹³ times faster than those in the disordered solid. Yet the molecular structure of the liquid is hardly distinguishable from that of the glass. Contrast this with the very different structure of an ordered solid, or crystal, in which the molecules are arranged in periodic arrays.

Liquids form glasses when they become very dense, and/or very cold. When this happens, the molecules become crowded, or ”jammed”, and cannot move unless their neighbours also move. This behaviour is similar to the crowded, concerted motion of people at a train station during rush hour. It is this increasing need for co-operativity in molecular motion that is thought to lie at the heart of the glass transition. Unfortunately, experimental techniques are not yet able to directly probe the motion of an individual molecule relative to a particular neighbour, or to directly observe the co-operative rearrangement of groups of molecules.