Y-type Hexaferrite Ba0 Research Articles

Switching of magnetoelectric states in the Y-type hexaferrite Ba0.5Sr1.5CoMgFe11AlO22

The multiferroic Y-type hexaferrites BaxSr2−xMe2Fe12−yAlyO22 (Me = Zn2+, Co2+, Mg2+, etc.) have attracted much attention due to their giant magnetoelectric (ME) effect up to room temperature and low modulated magnetic field by the chemical doping control of the complex magnetic phases. However, the research of substitution between the Me ions is rare. As doping at the Me ion site can combine the advantages of both, e.g., higher magnetic ordering temperature in Co2 and stronger ME coefficient in Mg2 Y-type hexaferrites, herein, we report the stability and switching of magnetoelectric states in the Y-type hexaferrites Ba0.5Sr1.5CoMgFe11AlO22 single crystals. Our results demonstrate that substituting half of the Mg2+ with Co2+ enhances the transition temperature of the alternating longitudinal conical phase to proper screw spin order up to room temperature compared to those Mg2 Y-type hexaferrites. Simultaneous occurrence of in-plane and out-of-plane ferroelectric polarization is observed, alongside comparable spontaneous magnetization. It was found that the in-plane spin-driven polarization can be reversible below 50 K with a substantial ME coefficient α = −8000 ps/m but becomes irreversible at 100 K. This reversal in the sign of the ME coefficient signifies the transition between two distinct ME states at high temperature. The reversibility and irreversibility of spin-induced polarization are discussed within the framework of free energy based on the ferroelectric phase, which prevail in numerous Y-type hexaferrites. Our results provide insights into understanding the role of the Me ions in the magnetoelectric coupling in Y-type hexaferrites.

Room-temperature giant magnetotranstance effect in Y-type hexaferrite Ba0.8Sr1.2Co2Fe11.1−xAl0.9CrxO22 (x ≤ 0.4)

We have investigated the magnetoelectric effect of a series of Y-type hexaferrite Ba0.8Sr1.2Co2Fe11.1−xAl0.9CrxO22 (x ≤ 0.4) at room temperature. Although the magnetoelectric voltage coefficient αE of these multiferroic hexaferrites is not high, it changes rapidly with an applied DC magnetic field, a phenomenon known as the giant magnetotranstance (GMT) effect. It is found that the GMT effect is enhanced with increasing content of Cr and reaches the maximum for x = 0.2. Specifically, the magnetotranstance ratio in the x = 0.2 sample is as high as −96% at 2000 Oe and −84% at 500 Oe. Further addition of Cr content causes a decay of the GMT effect. This kind of room-temperature GMT effect in Y-type hexaferrites opens up a route toward practical applications for the single-phase multiferroics.

Mutual control of electric and magnetic orders near room temperature in Al doped Y-type hexaferrite single crystals

Realizing robust magnetoelectric (ME) coupling effect near room temperature is still a long-standing challenge for the application of multiferroic materials in next-generation low-power spintronic and memory devices. Here we report a systematic study on the magnetic, dielectric, and ME coupling properties of Y-type hexaferrite Ba0.5Sr1.5Co2Fe12–xAlxO22 (x = 0.0, 0.5, 1.0) single crystals. The Al doping can induce the shifting of the alternating longitudinal conical (ALC)-proper screw (PS) magnetic phase transition temperature from 200 K for x = 0–365 K for x = 1.0. The most interesting feature is that the Ba0.5Sr1.5Co2Fe11AlO22 single crystal displays a direct and converse ME coupling coefficient with αH ∼3,100 ps/m and αE ∼3,900 ps/m at 250 K, respectively, due to the Al-doped enhanced stability of ALC phase. Moreover, the exchange bias also verifies the strong coupling of electric and magnetic orders. These results provide a valuable insight on the modulation of ALC structure and the mechanism of ME effect in Y-type hexaferrites.

Magnetocapacitance on the transition fields in Ni2+ doped Y-type hexaferrite Ba0.6Sr1.4Co2Fe11AlO22 obtained by high-energy ball milling

Y-type hexaferrites possess multiple magnetic phases that are temperature and magnetic-field dependent. Some of these phases are ferrimagnetic and also exhibit room temperature spin-driven ferroelectricity that corresponds to a type-II magnetoelectric. The temperature stability and the magnetic activation field of the multiferroic phases of Y-type hexaferrite can be tuned by substituting Co2+ sites with transition metal ions, such as Ni2+. The present work describes a simple method for obtaining Y-type hexaferrites using high-energy ball milling with heat treatment at relative low temperatures, compared with other methods, and evaluates the effect of nickel as dopant in Ba0.6Sr1.4Co2-xNixFe11AlO22, with x varying from 0 to 2.0 (Δx = 0.5), on the magnetic, dielectric, and magnetodielectric properties. The results show successful synthesis of pure hexagonal Y-type hexaferrite (R-3 m) by an easy and economical method. In addition, it is observed that nickel doping produces a diminution in the specific magnetization, a change in the magnetic thresholds of the magnetic phases, and an increase in space charge polarization. In addition, the magnetodielectric measurements also show different positive magnetocapacitance behaviors linked to the effect of doping on the magnetic and electronic structure.

Magnetoelectric phase diagram and magnetic field-induced reversal of electric polarization in Ba0.5Sr1.5Mg1.6Co0.4Fe12O22 single crystal

Multiferroic Y-type hexaferrites are single-phase compounds in which the electric polarization (P) is induced by a low magnetic field (H). In this study, Y-type hexaferrite Ba0.5Sr1.5Mg1.6Co0.4Fe12O22 single crystal was synthesized using Na2CO3-Fe2O3 flux. Their structural, magnetic, and magnetoelectric properties were investigated. The different transition temperatures between the H⊥c and H//c configurations showed that the direction of the applied H was important for the spin configurations. The M-H loops exhibited that the field-induced transitions could occur at room temperature (RT). A first-order magnetic phase transition around 250 K was unveiled from the Arrott plots. The P was non-zero at zero H below 50 K. By studying the magnetic field dependence of the dielectric properties at selected temperatures, a magnetoelectric phase diagram exhibiting the evolution of the spin-induced ferroelectric order with the Hab and temperature (T) was revealed. The magnetoelectric phase diagram showed that the polarization was reversed by the magnetic fields below 150 K where the H-induced ferroelectric order was maintained in a zero magnetic field.

Effect of Ni and Al substitution on the magnetic properties of Y-type hexaferrite Ba0.5Sr1.5Zn0.5Ni1.5Fe11.92Al0.08O22 powders

The effect is reported of substituting the non-magnetic Zn2+ cations with magnetic Ni2+ cations, and of the magnetic Fe3+ cations with non-magnetic Al3+ cations in Ba0.5Sr1.5Zn0.5Ni1.5Fe11.92Al0.08O22 on the resulting magnetic properties. The Y-type hexaferrite powders were synthesized by citric acid sol-gel auto-combustion, followed by appropriate thermal annealing. The saturation magnetization values (Ms ) in a magnetic field of 50 kOe were 36 emu/g and 30 emu/g at 4.2 K and 300 K, respectively. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization vs. temperature (4.2 – 300 K) were measured in dc magnetic fields of 50 Oe, 100 Oe and 500 Oe. The changes resulting from the dissimilar cationic substitutions were identified and discussed.

Magnetic phase transitions in Ba0.5Sr1.5Zn2Fe11.92Al0.08O22 hexaferrites

We report studies on the effect of substituting the magnetic Fe3+ cations with nonmagnetic Al3+ cations in Y-type hexaferrite Ba0.5Sr1.5Zn2Fe11.92Al0.08O22 powders on their magnetic properties and especially on the magnetic phase transitions responsible for observing the magnetoelectric effect. In this research, the Y-type hexaferrite powders were synthesized by citric acid sol-gel auto-combustion. After the auto-combustion process, the precursor powders were annealed at 1170 °C in air to obtain the Y-type hexaferrite materials. The effects of Al substitution on the structural, microstructural properties and phase content were investigated in detail using X-ray powder diffraction and scanning electron microscopy. Hysteresis measurements were performed by a physical-property-measurement-system (PPMS) (Quantum Design) at 4.2 K and at room temperature. Dc-magnetic measurements of the temperature dependence of the magnetization at magnetic fields of 50 Oe, 100 Oe and 500 Oe were used to determine the effect of applying a magnetic field on the temperature of magnetic-phase transitions. We demonstrated that the helical spin state can be modified further by varying the magnetic field.

Ni doping effect on the magnetic properties of polycrystalline Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12−xNixO22

The microstructure and magnetic properties of multiferrioc polycrystalline Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12−xNixO22 (BSZFNO, x = 0, 0.05, 0.1, 0.2, 0.35 and 0.5) synthesized by the solid-state reaction method are investigated. It is found that the shrink of BSZFNO lattice constant and the increase of grain size appear after substituting Fe ion with Ni ion, and Ni doping depresses the formation of Z-type and M-type impurity phases. BSZFNO undergoes two main magnetic phase transitions. Near room temperature, the temperature of phase transition from proper screw spin phase to collinear ferromagnetic phase increases with Ni amount increasing, suggesting the enhancement of exchange interaction of Fe(4)–O–Fe(5). The magnetic phase transition at lower temperature is attributed to the spin transition from a longitudinal conical spin order to a proper screw spin order, whose transition temperature varies due to different magnetocrystalline anisotropy with introducing Ni into BSZFO lattices. Furthermore, Ni doping leads to the expansion of the range of field-driven magnetic phases, especially intermediate-II and intermediate-III helical spin phase. The saturation magnetization at 5 K increases with Ni doping and arrives at a maximum value with Ni content x = 0.2, finally decreases with x. The increasing of the pitch of spin helix in initial Ni-doping leads to the enhancement of the magnetization. However, the conical spin phase eventually collapses in higher-concentration Ni-doping.

Magnetic and magnetoelectric properties of Y-type Ba0.6Sr1.4Zn2Fe12O22 hexaferrite single crystal

Magnetic and magnetoelectric properties of Y-type hexaferrite single crystal Ba0.6Sr1.4Zn2Fe12O22 were investigated using vibrating sample magnetometer and ferromagnetic resonance (FMR) techniques. It was found that this compound orders magnetically below 400 K and magnetization exhibits a sharp peak at 331 K, which corresponds to magnetic transition from collinear ferrimagnetic phase to a proper screw spin phase with decreasing temperature. Magnetic hysteresis measurements showed stepwise behavior of initial magnetization curve due to sequential metamagnetic transitions with increasing magnetic field. Using novel and sensitive method of electrically modulated FMR it was shown that this Y-type hexaferrite has significant magnetoelectric coupling, which was determined quantitatively at room temperature. Obtained results show that Y-type hexaferrite Ba0.6Sr1.4Zn2Fe12O22 has a rare combination of magnetoelectric coupling and large magnetization at room temperature, which is important for applications in magnetoelectric devices.

Reversal and non-reversal ferroelectric polarizations in a Y-type hexaferrite

The Cr ion doped Y-type hexaferrite Ba0.5Sr1.5Zn2Fe11.4Cr0.6O22 has been found to be a promising magnetoelectric material for the non-zero spontaneous electric polarization. A newly emerging transition at 183 K separates the low-field ferroelectric phase into two regions with reversal and non-reversal polarization respectively.

Indium doping effect on the magnetic properties of Y-type hexaferrite Ba0.5Sr1.5Zn2(Fe1-xInx)12O22

The effect of indium doping on structural and magnetic properties of Y-type hexaferrite Ba0.5Sr1.5Zn2(Fe1-xInx)12O22 (x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) prepared by the solid state reaction method was investigated. The Rietveld refinement method was used to analyze the X-ray diffraction patterns. The magnetic transition temperatures associated with the proper-screw spin phase to the collinear ferrimagnetic spin phase transition can be efficiently modulated by varying indium content. The magnetic transition temperature increases to a maximum with indium content x = 0.04 and then decreases with x, suggesting the possibility that electrically controlled magnetization reversal can be can be effectively tailored by varying indium content. The saturation magnetization at room temperature was decreased as increasing indium content, which can be explained as the metal ions occupation. It is worthy to note that the coercivity of In-doped samples was decreased drastically compared that of undoped sample, which is probably resulted from the reduction in anisotropy field with substitution of In3+ for Fe3+. The In-doped hexaferrite Ba0.5Sr1.5Zn2(Fe1-xInx)12O22 may be potential candidates for application in magnetoelectric devices.

Giant magnetoelectric effects achieved by tuning spin cone symmetry in Y-type hexaferrites

Multiferroics materials, which exhibit coupled magnetic and ferroelectric properties, have attracted tremendous research interest because of their potential in constructing next-generation multifunctional devices. The application of single-phase multiferroics is currently limited by their usually small magnetoelectric effects. Here, we report the realization of giant magnetoelectric effects in a Y-type hexaferrite Ba0.4Sr1.6Mg2Fe12O22 single crystal, which exhibits record-breaking direct and converse magnetoelectric coefficients and a large electric-field-reversed magnetization. We have uncovered the origin of the giant magnetoelectric effects by a systematic study in the Ba2-xSrxMg2Fe12O22 family with magnetization, ferroelectricity and neutron diffraction measurements. With the transverse spin cone symmetry restricted to be two-fold, the one-step sharp magnetization reversal is realized and giant magnetoelectric coefficients are achieved. Our study reveals that tuning magnetic symmetry is an effective route to enhance the magnetoelectric effects also in multiferroic hexaferrites.

Nonzero electric polarization and four magnetoelectric states at zero magnetic field in Cr-doped Y-type hexaferrite

We report here an enhanced magnetoelectric effect in a Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22 with Fe3+ ions partially substituted by magnetic Cr3+ ions (i.e., BSZFCO). The direct magnetoelectric effect is persistent up to 250 K, with the maximal susceptibility of ∼1309 ps/m at 75 K. More importantly, the pronounced non-zero electric polarization at zero magnetic field and four magnetoelectric states induced by different initial poling fields make it quite unique to serve in a magnetoelectric device. The stability of the direct (inverse) magnetoelectric effect is confirmed by the nonvolatile behavior in response to the cyclically sweeping magnetic (electric) fields. Our studies provide an insight into the nontrivial properties of BSZFCO, which are promising for multiferroic applications.

Mg doping effect on the magnetic properties of Y-type hexaferrite Ba0.5Sr1.5Zn2−xMgxFe12O22

The microstructure and magnetic properties of Mg-doped Ba0.5Sr1.5Zn2Fe12O22 hexaferrites synthesized by the solid state method are investigated. All the undoped and doped samples show a sharp screw proper spin phase to collinear ferrimagnetic spin phase transition above room temperature, and transition temperature increases distinctly with Mg doping. It is noteworthy that all the samples exhibit another magnetic phase transition at a lower temperature T1, which is associated with the longitudinal conical to the proper screw phase transition. The transition temperature T1 can be modulated by varying Mg content, indicating that the longitudinal conical spin phase is stabilized by the Mg-substitution. The saturation magnetization at room temperature increases to a maximum with Mg content x = 0.8 and then decreases with x. The variations of magnetic properties can be ascribed to the difference in the preferential site for Zn and Mg and different distribution of Fe3+ ions over tetrahedral and octahedral sites. It is worth noting that the range for the intermediate-III phase increases significantly as x increases to 2.0, suggesting that Mg-doped samples may be display field-induced ferroelectric order at temperature close to RT and in wide magnetic-field regions. The room-temperature M-H curves at lower applied field indicate that magnetic-field-induced ferroelectric phase can be stabilized at zero magnetic field by the substitution by Mg2+ for Zn2+. The Mg-doped hexaferrites Ba0.5Sr1.5Zn2Fe12O22 may be potential candidates for applying in magnetoelectric devices.

Magnetic field controllable electric polarization in Y-type hexaferrite Ba0.5Sr1.5Co2Fe12O22

We report the magnetic properties and the magnetoelectric effect in Y-type hexaferrite polycrystalline sample of Ba0.5Sr1.5Co2Fe12O22 (BSCFO). The magnetic critical temperature of BSCFO is 620 K, and the low-temperature helical magnetic order can hold up to 255 K. The isothermal magnetization curves sustain ferromagnetic hysteresis from 10 K to 300 K. Under external magnetic fields, the magnetic field induced electric polarization is observed up to 150 K. The magnitude and the sign of the electric polarization can be controlled by the applied magnetic field. These magnetic and magnetoelectric results provide the promise of the studied new hexaferrite as a potential multiferroic material.

Electric-field control of magnetization reversal in a Y-type hexaferrite

We report on the giant magnetoelectric effect in Y-type hexaferrite Ba0.5Sr1.5Zn2(Fe1−xInx)12O22 (x=0.08). Large electric field tuning of magnetism is observed near room-temperature. Electrically controlled magnetization reversal is observed at 315K. The sign of the magnetization exhibits an on–off behavior with the electric field. The scanning probe microscopy results show direct and powerful evidence of electric control of magnetism at room temperature.

Dielectric, magnetic, and lattice dynamics properties of Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22: Comparison of ceramics and single crystals

We prepared multiferroic Y-type hexaferrite Ba0.5Sr1.5Zn2Fe12O22 ceramics and compared their magnetic and dielectric properties with single crystal. Magnetic susceptibility and microwave resonance measurement revealed magnetic phase transition at TC=312 K, similar as in single crystal. Ferroelectric (FE) phase can be induced by external magnetic field in all investigated samples and the phase diagram in ceramics qualitatively resembles that of the single crystal. The range of magnetic fields, where the FE phase is induced, broadens after annealing of single crystal. Ceramics quenched after sintering exhibit several orders of magnitude lower conductivity than the single crystal. Heavily damped magnetic resonance was discovered in terahertz spectra at 10 K and its frequency softens below 5 GHz near TC. Number and symmetry of observed infrared (IR) and Raman active phonons correspond to paraelectric phase with D3d5 hexagonal structure. No evidence for a structural phase transition was found in the IR and Raman spectra on cooling (in zero magnetic field) or in the room-temperature IR spectra with external static magnetic field up to 0.3 T.