Low magnetic field reversal of electric polarization in a Y-type hexaferrite

Abstract

Magnetoelectric multiferroics in which ferroelectricity and magnetism coexist have attracted extensive attention because they provide great opportunities for the mutual control of electric polarization by magnetic fields and magnetization by electric fields. From a practical point view, the main challenge in this field is to find proper multiferroic materials with a high operating temperature and great magnetoelectric sensitivity. Here we report on the magnetically tunable ferroelectricity and the giant magnetoelectric sensitivity up to 250 K in a Y-type hexaferrite, BaSrCoZnFe 11 AlO 22 . Not only the magnitude but also the sign of electric polarization can be effectively controlled by applying low magnetic fields (a few hundreds of Oe) that modifies the spiral magnetic structures. The magnetically induced ferroelectricity is stabilized even in zero magnetic field. Decayless reproducible flipping of electric polarization by oscillating low magnetic fields is shown. The maximum linear magnetoelectric coefficient reaches a high value of ~ 3.0×10 3 ps/m at 200 K.In the past several years, spiral magnetic order induced multiferroics and magnetoelectric (ME) effects have been observed in a number of transition metal oxides such as TbMnO 3 , RMn 2 O 5 , CoCr 2 O 4 , and others [1][2][3] . In these spiral magnets, the magnetic order and ferroelectricity are inherently coupled and thus pronounced ME effects could be expected. 4,5 The microscopic mechanism has been well described with the spin current model 6 or the inverse Dzyaloshinskii-Moriya (DM) interaction model 7 . However, the ME effects in these spiral magnets are not useful for practical applications because they occur at low temperatures and require a large magnetic field of several tesla. Recently, the hexaferrites with helical spin order have been suggested as promising candidates for high temperature multiferroics. It was reported that some Y-type hexaferrites, such as (Ba,Sr) 2 Zn 2 Fe 12 O 22 and Ba 2 Mg 2 Fe 12 O 22 , can show magnetically induced ferroelectricity and pronounced ME effects due to modifications of spiral magnetic structures by applying magnetic fields [8][9][10][11] . Although the magnetic ordering temperatures of these Y-type hexaferrites are above room temperature, their ME effects are observable only below ~ 130 K. Subsequently, ME effects were also observed in Z-type 12,13 , M-type 14 , and U-type 15 hexaferrites.Especially, the low field ME effect in a Z-type hexaferrite, Sr 3 Co 2 Fe 24 O 41 , happens at room temperature, representing a big step towards practical applications 12. Nevertheless, there are still some critical problems to be overcome. For instance, although magnetic control of electric polarization at room temperature has been achieved, the reversal of electric polarization by magnetic fields has been realized only at low temperatures 10,11,14 . We prepared the Y-type hexaferrites by solid state reaction in oxygen. The as-sintered samples are not insulating enough at high temperatures, and thus a post-annealing...

Large reversible room-temperature magnetocaloric effect in the Ba0.5Sr1.5Zn2Fe12O22-related hexaferrites

“…4(a). The magnetization clearly shows three metamagnetic transitions with H increasing from 0 to 4.4 T. These sequential transitions may be roughly related to intermediate-І to Π, Π to Ш, and Ш to collinear ferromagnetic phase transitions, respectively, which is consistent with the previously reported results [16,18,22]. In the initial magnetization curves, the obvious kinks corresponding to H-induced metamagnetic transitions can be observed until 290 K (see Fig.…”

Analysis of the alternating current conductivity and magnetic behaviors for the polycrystalline Y-type Ba0.5Sr1.5Co2(Fe1-xAlx)12O22 hexaferrites

“…6,43 The present results clearly indicate that Al substitution has great effect on the magnetic transitions at the critical fields in the Co 2 Y ferrites.…”

“…With the increasing Al content, the steps become more significant. This kind of feature has also been observed in other Y-type hexaferrites, 6,7,13,43 which was suggested to result from the magnetic transitions, 44 i.e., from collinear ferrimagnetic phase to helix or intermediate phase.…”

Multiferroic and Magnetoelectric Hexagonal Ferrites

“…As can be seen in the Fig. 7.18c, d, both magnetisation and polarisation exhibited stepped hysteresis loops indicating Right a oscillating ME current, b switching of polarisation and c variation of applied magnetic field with time [88] competing phase transitions with applied magnetic field, and there is a small M r and significant P (*25 lC m -2 ) at zero field (B = 0). P increased to a sizeable 100 lC m -2 with B = 0.02T at 4.3 K. It was shown that the ferroelectric-like switch in polarisation occurs in the plane of the crystal, perpendicular to the c-axis about which the helical magnetisation is oriented, and it was suggested that the change in magnetisation character around 0.13 T was due to a switch from the helical c-axis magnetisation to the direction of the applied field, as seen with BSZY [89].…”

“…7.17). This gave a large ME coefficient of 3,000 ps m -1 at a relatively high temperature of 200 K, with a low field of 0.01 T required to reverse the polarisability [88].…”