
temperature range of the observation of the phenom-
enon, are the weak points of this system. Anyhow, it
represents the first example of fine-tuning of long-
range magnetic ordering by light. Photomagnetic
studies on related materials using different alkali cat-
ions are in progress to further explore this fascinating
phenomenon.
6. Concluding Remarks
The photo-control of the magnetic and optical prop-
erties remains a challenging topic in material science
in view of the possible implementation in optical
switching and memory devices. Various examples be-
longing to this appealing class of materials have been
covered in this article. There are no doubts that a
sizeable number of new compounds, as well as new
photophysical phenomena, may emerge in the near
future from this rapidly evolving field. We can, for
instance, mention a novel composite material com-
prising Prussian blue intercalated into photorespon-
sive vesicles based on azobenzene moieties, whose
magnetic properties can be controlled by photoillu-
mination (Einaga et al. 1999) or a nitrosyl derivative,
trans-[Ru(en)
2
(H
2
O)(NO)]Cl
3
(en ¼ethylenediamine)
which show a remarkably long lived metastable state
up to 267 K (Kawano et al. 2000).
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Pnictides and Chalcogenides: Transition
Metal Compounds
Research on the magnetic properties of 3d transition
metal pnictides and chalcogenides has advanced
enormously. Realistic energy band calculations as
well as experimental techniques such as photoemis-
sion spectroscopy are available and play an impor-
tant role in clarifying the variety of magnetic and
related electronic characteristics. Chalcogens (M)
(pnicogens (M
0
)), elements from the 6a (5a) group
of the periodic table, have a valence electron config-
uration ns
2
np
4
(ns
2
np
3
). The former group includes
oxygen, sulfur, selenium, tellurium, and polonium
and the latter nitrogen, phosphorus, arsenic, anti-
mony, and bismuth. Chalcogens and pnicogens form
many compounds with 3 d elements. The total number
1062
Pnictides and Chalcogenides: Transition Metal Compounds