Structural, Dielectric and Raman Spectroscopic Study of Complex Electric and Magnetic Interactions in Multiferroic Ionic Crystals

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While ordinary materials are usually either magnetically or electrically ordered, a relatively new class of materials of so-called multiferroics has been discovered that exhibits magnetic and electrical (and eventually also mechanical) ordering simultaneously. The unique and fascinating feature of these systems is that both phenomena are coupled and that electric forces may be used to control the magnetic structure and vice versa.
Unfortunately, most systems that have been investigated so far exhibit these extraordinary properties only at low temperatures. In view of possible applications in information technology, sensor technology etc., it is, therefore, a crucial task to increase the temperature range of multiferroics. Since the exact mechanism of spin coupling with the movement of ions and the resulting electric dipole moment is still not fully understood, detailed experimental and theoretical studies are needed which require advanced techniques like high-resolution Raman spectroscopy with suitable laser sources.

More detailed information about the variation of interatomic interactions can be obtained by Raman spectroscopy. Unlike the previous study on pure MnWO4, however, the mixed crystalline system cannot be investigated using the standard argon laser since the molybdenum content makes the sample entirely opaque and strongly absorbs green light.

As a consequence, a green laser is inappropriate for this system and a red one must be preferred. In Raman spectroscopy ( , fundamental conditions of the exciting light are long-time stability as well as a narrow bandwidth of about 0.01 cm–1. Hence, we used a novel solid-state red laser Solo 640 (UNIKLASERS) ( , which meets these requirements very well. This laser has a wavelength of λ = 640 nm and a maximum power of 500 mW (at the sample, 10 mW are applied).