This paper developed the theory about the interplay between the magnetism and ferroelectricity in material which opened the possibility new type of electric magnetic devices.
‘Spin Current and Magnetoelectric Effect in Noncollinear Magnets’ http://prl.aps.org/abstract/PRL/v95/i5/e057205
Throughout the history of material science, magnet has been used by applying magnetic field, ferroelectric material has been used by applying electric field. That makes sense. But, what if we could control magnet by electric field or control ferroelectric material by magnetic field? We will have much wider option to make useful component by using the phenomena that we call it magnetoeletric (ME) effect.
The ME effect is a phenomenon in which the magnetization is induced by the electric field or the electric field induced by magnetic field. Firstly, Pierre Curie surmised ME effect in 1894[1]. And then, the phenomenological theory of the ME effect was developed Landau [2] and Dzyaloshinskii [3] that was about 50 years ago. There the symmetry consideration is essential to classify ME effect via magnetic point group. Especially time reversal and spatial inversion are key symmetries to the ME effect. After these theories developed, ME effect in several materials has been discovered. However, it is difficult to apply to product because that effect is too small to apply. Scientists need more concrete plan to study ME effect. A fully microscopic theory based on the electricity state was still missing. However, this group developed theory of the ME effect starting from the electric Hamiltonian taking into account the spin-orbit interaction. That opened new possibility.
Putting aside the detailed calculation, the most important result of this paper is this equation. They could simplify the phenomena in the equation as following
P_ij=A e_ij×(e_i×e_j ) —- (1)
This equation gave the experimentalist helpful suggestion. That suggestion said ‘Look for spiral magnetic materials’. As shown Fig. 1, the theory showed that the spiral magnetic material can produce ferroelectricity. Because of its simplicity, so many material experimental scientists could have worked finding the new material. They found more than 8 within 2 years after this paper published. And these materials had been studied 5 years, now the companies are going to apply this material to the products.
Fig. 1 The spiral magnetic structure and ferroelectricity.
Some experimentalists found the material which does not follow this equation, so that someone develop several theory to explain these exception but, we might not have found so many maltiferroic material and the supplemental theories if this simple suggestion had never not existed.
Unfortunately, for the application we need to time to research and development at company level. But we will get unexpected cool product soon.
[1] P. Curie: J. Phys. (Paris) 3 (1894) 393.
[2] L. D. Landau and E. Lifshitz, Electrodynamics of Continuous Media (Butterworth-Heinemann, Oxford, 2002), p. 176.
[3] I. E. Dzyaloshinskii, Sov. Phys. JETP 10, 628 (1960).