The experimental studies of magnetoelectric effects in pulse magnetic field up to 250 kOe and their theoretical analysis on the basis of magnetic symmetry consideration are carried out. It is shown that the nonvanishing components of quadratic magnetoelectric effect tensor corresponding to the electric polarization along b- and c-axes point out the triclinic distortion of the crystal symmetry. Anomalous temperature dependence of magnetically induced polarization Pa(Hb) testifies to the magnetically induced pyroelectric effect. The torque curves measurements show the deflection of the spin orientation from the b-axis at 9 degrees of arc.
Neutron diffraction with static and pulsed magnetic fields is used to directly probe the magnetic structures in LiNiPO$_4$ up to 25T and 42T, respectively. By combining these results with magnetometry and electric polarization measurements under puls
ed fields, the magnetic and magnetoelectric phases are investigated up to 56T applied along the easy $c$-axis. In addition to the already known transitions at lower fields, three new ones are reported at 37.6, 39.4 and 54T. Ordering vectors are identified with ${bf Q}_{mathrm{VI}}$ = (0, 1/3, 0) in the interval 37.6--39.4T and ${bf Q}_{mathrm{VII}}$ = (0, 0, 0) in the interval 39.4-54T. A quadratic magnetoelectric effect is discovered in the ${bf Q}_{mathrm{VII}}$ = (0, 0, 0) phase and the field-dependence of the induced electric polarization is described using a simple mean-field model. The observed magnetic structure and magnetoelectric tensor elements point to a change in the lattice symmetry in this phase. We speculate on the possible physical mechanism responsible for the magnetoelectric effect in LiNiPO4.
We incorporate single crystal Fe$_3$O$_4$ thin films into a gated device structure and demonstrate the ability to control the Verwey transition with static electric fields. The Verwey transition temperature ($T_V$) increases for both polarities of th
e electric field, indicating the effect is not driven by changes in carrier concentration. Energetics of induced electric polarization and/or strain within the Fe$_3$O$_4$ film provide a possible explanation for this behavior. Electric field control of the Verwey transition leads directly to a large magnetoelectric effect with coefficient of 585 pT m/V.
We present a unique example of giant magnetoelectric effect in a conventional multiferroic HoMnO3, where polarization is very large (~56 mC/m2) and the ferroelectric transition temperature is higher than the magnetic ordering temperature by an order.
We attribute the uniqueness of the giant magnetoelectric effect to the ferroelectricity induced entirely by the off-center displacement of rare earth ions with large magnetic moments. This finding suggests a new avenue to design multiferroics with large polarization and higher ferroelectric transition temperature as well as large magnetoelectric effects.
Magneto-capacitance effect was investigated using the impedance spectroscopy on single crystals of LuFe2O4. The intrinsic impedance response could be separated from the interfacial response and showed a clear hysteresis loop below TFerri ~ 240 K unde
r the magnetic field. The neutron diffraction experiment under the magnetic field proves the origin of dielectric property related to the motion of nano-sized ferromagnetic domain boundary. These results imply that the modification of the microscopic domain structure is responsible for the magnetoelectric effect in LuFe2O4.
We report the discovery of a metamagnetic phase transition in a polar antiferromagnet Ni$_3$TeO$_6$ that occurs at 52 T. The new phase transition accompanies a colossal magnetoelectric effect, with a magnetic-field-induced polarization change of 0.3
$mu$C/cm$^2$, a value that is 4 times larger than for the spin-flop transition at 9 T in the same material, and also comparable to the largest magnetically-induced polarization changes observed to date. Via density-functional calculations we construct a full microscopic model that describes the data. We model the spin structures in all fields and clarify the physics behind the 52 T transition. The high-field transition involves a competition between multiple different exchange interactions which drives the polarization change through the exchange-striction mechanism. The resultant spin structure is rather counter-intuitive and complex, thus providing new insights on design principles for materials with strong magnetoelectric coupling.
A.K. Zvezdin
,G.P. Vorobev
,A.M. Kadomtseva
.
(2008)
.
"Quadratic Magnetoelectric Effect and Magnetic Field Induced Pyroelectric Effect in Multiferroic BaMnF4"
.
Aleksandr Pyatakov P.
هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا