So Young Haam

Realization of giant magnetoelectricity in helimagnets.

We show that low field magnetoelectric (ME) properties of helimagnets Ba0.5Sr1.5Zn2(Fe1-xAlx)12O22 can be efficiently tailored by the Al-substitution level. As x increases, the critical magnetic field for switching electric polarization is systematically reduced from approximately 1 T down to approximately 1 mT, and the ME susceptibility is greatly enhanced to reach a giant value of 2.0x10{4} ps/m at an optimum x=0.08. We find that control of the nontrivial orbital moment in the octahedral Fe sites through the Al substitution is crucial for fine-tuning the magnetic anisotropy and obtaining the conspicuously improved ME characteristics.

Electric field control of nonvolatile four-state magnetization at room temperature.

We find the realization of large converse magnetoelectric (ME) effects at room temperature in a magnetoelectric hexaferrite Ba0.52Sr2.48Co2Fe24O41 single crystal, in which rapid change of electric polarization in low magnetic fields (about 5 mT) is coined to a large ME susceptibility of 3200 ps/m. The modulation of magnetization then reaches up to 0.62μ(B)/f.u. in an electric field of 1.14 MV/m. We find further that four ME states induced by different ME poling exhibit unique, nonvolatile magnetization versus electric field curves, which can be approximately described by an effective free energy with a distinct set of ME coefficients.

Low-magnetic-field control of dielectric constant at room temperature realized in Ba0.5Sr1.5Zn2Fe12O22

We show that the room temperature resistivity of Ba0.5Sr1.5Zn2Fe12O22 single crystals increases by more than three orders of magnitude upon being subjected to optimized heat treatments. The increase in the resistivity allows the determination of magnetic field (H)-induced ferroelectric phase boundaries up to 310?K through measurements of dielectric constant at a frequency of 10?MHz. Between 280 and 310?K, the dielectric constant curve shows a peak centered at zero magnetic field and thereafter decreases monotonically up to 0.1?T, exhibiting a magnetodielectric effect of 1.1%. This effect is ascribed to the realization of magnetic field-induced ferroelectricity at an H value of less than 0.1?T near room temperature. Comparison between electric and magnetic phase diagrams in wide temperature- and field-windows suggests that the magnetic field for inducing ferroelectricity has decreased near its helical spin ordering temperature around 315?K due to the reduction of spin anisotropy in Ba0.5Sr1.5Zn2Fe12O22.

Observation of a multiferroic critical end point

The study of abrupt increases in magnetization with magnetic field known as metamagnetic transitions has opened a rich vein of new physics in itinerant electron systems, including the discovery of quantum critical end points with a marked propensity to develop new kinds of order. However, the electric analogue of the metamagnetic critical end point, a “metaelectric” critical end point, has been rarely studied. Multiferroic materials wherein magnetism and ferroelectricity are cross-coupled are ideal candidates for the exploration of this novel possibility using magnetic-field (H) as a tuning parameter. Herein, we report the discovery of a magnetic-field-induced metaelectric transition in multiferroic BiMn2O5, in which the electric polarization (P) switches polarity along with a concomitant Mn spin–flop transition at a critical magnetic field Hc. The simultaneous metaelectric and spin–flop transitions become sharper upon cooling but remain a continuous cross-over even down to 0.5 K. Near the P = 0 line realized at μ0Hc ≈ 18 T below 20 K, the dielectric constant (ɛ) increases significantly over wide field and temperature (T) ranges. Furthermore, a characteristic power-law behavior is found in the P(H) and ɛ(H) curves at T = 0.66 K. These findings indicate that a magnetic-field-induced metaelectric critical end point is realized in BiMn2O5 near zero temperature.

Strong magnetoelastic effect on the magnetoelectric phenomena of TbMn 2 O 5

Comparative studies of magnetoelectric susceptibility (

A new heat capacity measurement scheme based on the scanning relaxation method for the Si–N membrane microcalorimeter at high temperatures up to 700 K

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Electric field control of nonvolatile four-state magnetization at room temperature

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Realization of full magnetoelectric control at room temperature

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Strong magnetoelastic effect on the magnetoelectric phenomena

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Publisher's Note: Realization of Giant Magnetoelectricity in Helimagnets [Phys. Rev. Lett. 104,037204 (2010)]

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