Magnetic control of large room-temperature polarization.

Numerous authors have referred to room-temperature magnetic switching of large electric polarizations as 'the Holy Grail' of magnetoelectricity. We report this long-sought effect, obtained using a new physical process of coupling between magnetic and ferroelectric nanoregions. Solid state solutions of PFW [Pb(Fe(2/3)W(1/3))O(3)] and PZT [Pb(Zr(0.53)Ti(0.47))O(3)] exhibit some bi-relaxor qualities, with both ferroelectric relaxor characteristics and magnetic relaxor phenomena. Near 20% PFW the ferroelectric relaxor state is nearly unstable at room temperature against long-range ferroelectricity. Here we report magnetic switching between the normal ferroelectric state and a magnetically quenched ferroelectric state that resembles relaxors. This gives both a new room-temperature, single-phase, multiferroic magnetoelectric, (PbFe(0.67)W(0.33)O(3))(0.2)(PbZr(0.53)Ti(0.47)O(3))(0.8) ('0.2PFW/0.8PZT'), with polarization, loss (<1%), and resistivity (typically 10(8)-10(9) Ω cm) equal to or superior to those of BiFeO(3), and also a new and very large magnetoelectric effect: switching not from +P(r) to -P(r) with applied H, but from P(r) to zero with applied H of less than a tesla. This switching of the polarization occurs not because of a conventional magnetically induced phase transition, but because of dynamic effects: increasing H lengthens the relaxation time by 500 × from<200 ns to>100 µs, and it strongly couples the polarization relaxation and spin relaxations. The diverging polarization relaxation time accurately fits a modified Vogel-Fulcher equation in which the freezing temperature T(f) is replaced by a critical freezing field H(f) that is 0.92 ± 0.07 T. This field dependence and the critical field H(c) are derived analytically from the spherical random bond random field model with no adjustable parameters and an E(2)H(2) coupling. This device permits three-state logic (+P(r),0,-P(r)) and a condenser with >5000% magnetic field change in its capacitance; for H = 0 the coercive voltage is 1.4 V across 300 nm for +P(r) to -P(r) switching, and the coercive magnetic field is 0.5 T for +P(r) to zero switching.