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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. [ABSTRACT FROM AUTHOR]

With the discovery of two-dimensional (2D) ferroelectricity and ferromagnetism in van der Waals (vdW) materials, there has been significant interest in 2D multiferroics. Herein, we report the occurrence of weak ferromagnetism and magnetoelectricity in vdW antiferromagnet MnPSe3 single crystals. Our results demonstrate that MnPSe3 undergoes an antiferromagnetic transition at the Néel temperature TN = 70 K with weak ferromagnetism along the [1–10] direction. Detailed magnetoelectric (ME) data show that MnPSe3 exhibits a linear ME tensor αij with nine nonzero components. Additionally, a magnetically induced electric polarization as large as 98.5 μC/m2 is observed along the [110] direction, with a ME coefficient of 13.5 ps/m at 10 K for a magnetic field of 9 T applied along the [110] direction. Importantly, we discuss our experiments based on symmetry and microscopic analysis, thereby suggesting that the spin-dependent p-d hybridization mechanism plays an important role in the emergence of magnetic-field-induced ferroelectricity. Hence, our findings provide insights for exploring the ME coupling in vdW materials. [ABSTRACT FROM AUTHOR]

Recently, two-dimensional van der Waals ferroelectrics have been receiving much interest with continuous exploration of the underlying physics and device applications. While α-In2Se3 in an atomically thin crystal form is believed to have nonzero out-of-plane polarization, its ferroelectric (FE) instability in competition with the antiferroelectric (AFE) ground state is highly concerned. Along this line, a bilayer α-In2Se3 structure should be a good object for clarifying this issue since it is the simplest 2D lattice accommodating an AFE state, possibly allowing the AFE–FE competition. In this work, we employ the first-principles calculation to investigate the lattice and electronic structures of bilayer α-In2Se3, and special attention is paid to the FE instability in competition with the AFE ground state. It is found that the energy difference between the AFE ground state and FE state is small, thereby allowing an electric field modulation of the AFE–FE inter-conversion. More importantly, the Hyed–Scuseria–Ernzerhof algorithm predicts that the FE state is indeed semiconducting rather than metallic, removing the inconsistency between experimental observation and theoretical prediction. The spin–orbital coupling effect can further enlarge the bandgap and drive the indirect-to-direct bandgap transition, and thus appears to be an important ingredient of the underlying physics. [ABSTRACT FROM AUTHOR]

The topologically protected vortex–antivortex (V–AV) domain structure in ferroelectric hexagonal manganites has been highly concerned recently, but its stability against intrinsic defects remains to be understood, given the claim that a topological structure would be robust against defects and other perturbations. In fact, it is also known that the V–AV structure is sensitive to the sample quality, and such a well-developed structure is hardly observed in thin films and defective single crystals. In this work, we investigate the influence of anti-trimer point defects on the stability of the V–AV domain structure by employing the phase-field simulation based on the Landau–Devonshire phenomenological theory. It is revealed that the characteristic V–AV structure essentially relies on the anti-trimer point defects under consideration. These defects lower the trimerization transition temperature on one hand and produce pinning effect on the vortex cores/walls on the other hand. However, the V–AV structure does remain robust if the anti-trimer magnitude of these defects is relatively weak but will be eventually destroyed if the anti-trimer magnitude is strong. [ABSTRACT FROM AUTHOR]

Charge-ordered layered manganites ReA2Mn2O7 (Re = rare-earth species and A = Ca, Sr, Ba, etc.) are believed to offer a number of fascinating electronic and magnetic properties, including the long-time claimed but not yet confirmed ferroelectricity associated with charge-ordering. Experimental observations of the charge-order induced transport and electrically polar behaviors have been insufficient. In this work, we synthesize the La(Ca0.8Sr0.2)2Mn2O7 (LCSMO) single crystal and investigate its structural, magnetic, and dielectric properties. It is revealed that LCSMO undergoes two consecutive charge-ordering transitions upon decreasing temperature T before entering an antiferromagnetic state in the low-T range. The first charge-order transition occurs at temperature TCO1 ∼ 314 K from the high-T paramagnetic state. This charge-order state (CO1 state) is transferred into another charge-order state (CO2 state) by a sequence starting from ∼290 K, and the resultant CO2 state is dynamic and polar-like. The dynamic behaviors of this polar-like CO2 state is confirmed by the remarkable dielectric relaxation associated with this state. The present work provides a connection between the charge-ordering and electrically polar response in LCSMO, while ferroelectricity remains yet to be an issue. [ABSTRACT FROM AUTHOR]

Magnetically induced ferroelectric polarization in rare-earth RMn2O5 manganites is believed to originate from the symmetric exchange striction associated with a specific antiferromagnetic phase in the low temperature (T) region and would be irrelevant with electropoling in the high-T paramagnetic-paraelectric phase region. In this work, we demonstrate that low-T pyroelectric polarization of GdMn2O5 single crystals along the b axis in the antiferromagnetic phase exhibits remarkable dependence on the electropoling history imposed in the high-T paramagnetic-paraelectric phase. In particular, the high-T electropoling results in a reversal of ferroelectric polarization in the low-T region, which can be flopped back by the electropoling being sustained in the low-T ferroelectric region. The existence of an electrically polarizable magnetic cluster state in the high-T paramagnetic-paraelectric region is proposed based on a combination of experimental observations and first-principles calculations. An intrinsic correlation between the low-T antiferromagnetic ordering and the high-T polarizable state is discussed. The present experiments unveil the emergent phenomena on multiferroicity of RMn2O5 and suggest an alternative scenario for electrocontrol of magnetism. [ABSTRACT FROM AUTHOR]

Magnetically induced ferroelectric polarization in rare-earth RMn2O5 manganites is believed to originate from the symmetric exchange striction associated with a specific antiferromagnetic phase in the low temperature (T) region and would be irrelevant with electropoling in the high-T paramagnetic-paraelectric phase region. In this work, we demonstrate that low-T pyroelectric polarization of GdMn2O5 single crystals along the b axis in the antiferromagnetic phase exhibits remarkable dependence on the electropoling history imposed in the high-T paramagnetic-paraelectric phase. In particular, the high-T electropoling results in a reversal of ferroelectric polarization in the low-T region, which can be flopped back by the electropoling being sustained in the low-T ferroelectric region. The existence of an electrically polarizable magnetic cluster state in the high-T paramagnetic-paraelectric region is proposed based on a combination of experimental observations and first-principles calculations. An intrinsic correlation between the low-T antiferromagnetic ordering and the high-T polarizable state is discussed. The present experiments unveil the emergent phenomena on multiferroicity of RMn2O5 and suggest an alternative scenario for electrocontrol of magnetism. [ABSTRACT FROM AUTHOR]

The rare-earth double-perovskite R2CoMnO6 family has been reported to be promising multiferroics where the predicted ferroelectric polarization along the b-axis is induced by the Co2+/Mn4+ collinear magnetic order. In this work, we report our characterizations on the structural, magnetic, dielectric, and ferroelectric behaviors of flux-grown Y2CoMnO6 single crystals. A weak ferromagnetic transition with the Curie point TC ∼ 70 K is evident in combination with a remarkable magnetic hysteresis loop along the c-axis. The earlier reported dielectric anomaly at the magnetic transition is not detected in our single crystals. In addition, the peak of each electric current curve as a function of temperature, probed along different crystallographic directions, shows serious shifting with the temperature ramping rate, excluding the intrinsic ferroelectric contribution. The measured data are not in conformity with theoretical predictions and earlier experiments on polycrystalline samples. In addition, no reliable sign for magnetoelectric coupling can be detected. The present work seems to exclude the existence of magnetism-driven ferroelectricity in Y2CoMnO6. [ABSTRACT FROM AUTHOR]

Hubnerite MnWO4 is a highly frustrated magnetic compound that has been known for its multiferroic properties. The intrinsic connection of ferroelectric polarization and magnetically frustrated structure allows an opportunity to probe the stability of magnetic structures against perturbations by means of measuring ferroelectric polarization. In this work, we investigate the ferroelectric polarization of Mn1 − 2xIrxWO4 to probe the stability of the low-temperature (T) collinear antiferromagnetic (AF1) phase against the Ir substitution, considering the strong spin-orbital coupling of Ir4+ that would enhance the single-ion anisotropy, on the one hand, and would favor the noncollinear spin alignment, on the other hand. Different from Mn1 − xRux/2WO4, it is suggested that the AF1 phase is only partially suppressed by the Ir substitution, allowing the emergence of the noncollinear antiferromagnetic (AF2) phase in coexistence with the collinear AF1 phase. Proper Ir substitution may promote both the magnetocrystalline anisotropy and the Dzyaloshinskii-Moriya interaction, thus making the modulation of the magnetic structure more complicated. [ABSTRACT FROM AUTHOR]

Hubnerite MnWO4 is a highly frustrated magnetic compound that has been known for its multiferroic properties. The intrinsic connection of ferroelectric polarization and magnetically frustrated structure allows an opportunity to probe the stability of magnetic structures against perturbations by means of measuring ferroelectric polarization. In this work, we investigate the ferroelectric polarization of Mn1 − 2xIrxWO4 to probe the stability of the low-temperature (T) collinear antiferromagnetic (AF1) phase against the Ir substitution, considering the strong spin-orbital coupling of Ir4+ that would enhance the single-ion anisotropy, on the one hand, and would favor the noncollinear spin alignment, on the other hand. Different from Mn1 − xRux/2WO4, it is suggested that the AF1 phase is only partially suppressed by the Ir substitution, allowing the emergence of the noncollinear antiferromagnetic (AF2) phase in coexistence with the collinear AF1 phase. Proper Ir substitution may promote both the magnetocrystalline anisotropy and the Dzyaloshinskii-Moriya interaction, thus making the modulation of the magnetic structure more complicated. [ABSTRACT FROM AUTHOR]

BiFeO3 represents the most extensively investigated multiferroic due to its fascinating ferroelectric domain structures, large polarization, and multiferroic coupling, among many other emergent phenomena. Nevertheless, much less concern with the piezoelectricity has been raised while all these well addressed properties are identified in thin film BiFeO3, and bulk ceramic BiFeO3 has never been given priority of attention. In this paper, we report our experiments on the ferroelectric and piezoelectric properties as well as domain structures of BiFeO3 bulk ceramics synthesized by rapid hot-press sintering. It is revealed that these properties are strongly dependent on the microstructural quality, and the largest piezoelectric coefficient d33 = 55 pC/N with electric polarization as large as 45 μC/cm2 is obtained for the sample sintered at 800 °C, while they are only 30 pC/N and 14 μC/cm2 for the samples sintered in normal conditions at 800 °C. The two-level hierarchical stripe-like and irregular dendrite-like domain structures are observed in these hot-press sintered samples. It is suggested that the enhanced piezoelectric property is ascribed to the two-level hierarchical stripe-like domain structure which may respond more easily to electrical and strain stimuli than those irregular dendrite-like domains. The enhanced remnant polarization should be owing to the improved sample quality and large grains in the properly hot-press sintered samples. [ABSTRACT FROM AUTHOR]

The one-step drawing process of double-box flume was simulated by finite element method(FEM). It was found that major defects in the forming process were vertical surface fractures in the box and material accumulation near rounded corners. The optimal forming parameters were obtained by optimizing and improving workpiece, single factor analysis and orthogonal experiment optimization. Guiding grooves with an included angle of 140° and a depth of 1 mm was designed in the blank holder to guide materials from accumulation area to insufficient area, thus reducing material fractures and improving deep drawing. The ultimate depth of one-step drawing without defects was increased to 190 mm by optimizing process parameters and improving structure. [ABSTRACT FROM AUTHOR]

Linear magnetoelectrics refer to those compounds in which ferroelectric (FE) polarization can be generated by applying the magnetic field. This scenario opens an additional avenue toward high-temperature magnetoelectric (ME) coupling that is achievable in a large class of relatively weak frustrated magnetic systems such as honeycomb antiferromagnets. It is, thus, urgent to unveil the physics underlying the linear ME coupling in these linear ME materials. We grow the single crystals of Mn4Nb2O9, a linear ME candidate with high magnetic ordering temperature, and carry out a set of structural, magnetic, and ME characterizations. An antiferromagnetic ordering with [001]-oriented moments at the Neel point TN = 109 K is identified together with magnetic field driven large electric polarization emerging at TN, due to the strong exchange striction dependent mechanism. The measured ME coupling tensor α fits well the magnetic symmetry −3′m′, consistent with the linear ME scenario. Furthermore, remarkable responses of FE polarization and magnetization to the magnetic field and electric field, respectively, are demonstrated. [ABSTRACT FROM AUTHOR]

Linear magnetoelectrics refer to those compounds in which ferroelectric (FE) polarization can be generated by applying the magnetic field. This scenario opens an additional avenue toward high-temperature magnetoelectric (ME) coupling that is achievable in a large class of relatively weak frustrated magnetic systems such as honeycomb antiferromagnets. It is, thus, urgent to unveil the physics underlying the linear ME coupling in these linear ME materials. We grow the single crystals of Mn4Nb2O9, a linear ME candidate with high magnetic ordering temperature, and carry out a set of structural, magnetic, and ME characterizations. An antiferromagnetic ordering with [001]-oriented moments at the Neel point TN = 109 K is identified together with magnetic field driven large electric polarization emerging at TN, due to the strong exchange striction dependent mechanism. The measured ME coupling tensor α fits well the magnetic symmetry −3′m′, consistent with the linear ME scenario. Furthermore, remarkable responses of FE polarization and magnetization to the magnetic field and electric field, respectively, are demonstrated. [ABSTRACT FROM AUTHOR]

With the discovery of two-dimensional (2D) ferroelectricity and ferromagnetism in van der Waals (vdW) materials, there has been significant interest in 2D multiferroics. Herein, we report the occurrence of weak ferromagnetism and magnetoelectricity in vdW antiferromagnet MnPSe3 single crystals. Our results demonstrate that MnPSe3 undergoes an antiferromagnetic transition at the Néel temperature TN = 70 K with weak ferromagnetism along the [1–10] direction. Detailed magnetoelectric (ME) data show that MnPSe3 exhibits a linear ME tensor αij with nine nonzero components. Additionally, a magnetically induced electric polarization as large as 98.5 μC/m2 is observed along the [110] direction, with a ME coefficient of 13.5 ps/m at 10 K for a magnetic field of 9 T applied along the [110] direction. Importantly, we discuss our experiments based on symmetry and microscopic analysis, thereby suggesting that the spin-dependent p-d hybridization mechanism plays an important role in the emergence of magnetic-field-induced ferroelectricity. Hence, our findings provide insights for exploring the ME coupling in vdW materials. [ABSTRACT FROM AUTHOR]

To improve mechanical properties of asymmetrical hollow shafts parts, the dynamic recrystallization of asymmetrical hollow shaft can be obtained by cross wedge rolling (CWR) technology. The Finite element model (FEM) is established using the DEFORM-3D software, the distribution of the dynamic recrystallization volume fraction is illustrated, and the law of average grain size distribution is analyzed. The microscopy results indicate that the grain size at the central area of cross-section is larger than that at lateral area, and the grain of the central part can be obviously refined, the whole microstructure homogeneity is improved, which have provided theoretical foundation for further improving the quality and mechanical properties of CWR asymmetrical hollow shafts parts. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

OBJECTIVE: Previous studies have demonstrated the importance of stem cells inhuman cancer, including colon cancer. Pitavastatin is approved for the treatment of hyperlipidemia and has also been shown to inhibit stem cell proliferation in preliminary in vitro studies. This study was done to investigate the effects of pitavastatin on human colon carcinoma stem cells (coCSCs) in vitro and in mouse tumor xenografts in vivo. MATERIALS AND METHODS: Human colon adenocarcinoma cell lines, SW480 and SW620, were cultured to the spheroid formation. The effects of pitavastatin on colon cancer stem cells were studied using the colorimetric MTT cell proliferation assay; quantitative polymerase chain reaction was used to determine the expression of cell cycle genes, OCT4, SOX2, and NANOG; Western blots were performed to measure MDR1. Mice were injected subcutaneously with SW480 cells; the growth of these tumor xenografts was studied using volumetric analysis following pitavastatin treatment. RESULTS: Specific cell culture medium provided conditions that resulted in the expression of colon cancer stem cell markers when compared with normal cultured cells. Colon cancer stem cells were inhibited by pitavastatin treatment. Pitavastatin reduced the expression of stem cell markers of colon cancer stem cells and induced the cell apoptosis. Pitavastatin inhibited the growth of mouse tumor xenografts. CONCLUSIONS: The findings of this preliminary study have demonstrated a potential role for pitavastatin in the inhibition of stem cell proliferation in colon carcinoma. Further studies are recommended to determine the mechanism of these effects on colon carcinoma cells in vitro and in vivo. [ABSTRACT FROM AUTHOR]