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Unveiling hidden ferrimagnetism and giant magnetoelectricity in polar magnet Fe2Mo3O8.

Wang Y, Pascut GL, Gao B, Tyson TA, Haule K, Kiryukhin V, Cheong SW - Sci Rep (2015)

Bottom Line: Magnetoelectric (ME) effect is recognized for its utility for low-power electronic devices.Largest ME coefficients are often associated with phase transitions in which ferroelectricity is induced by magnetic order.The observed effects are associated with a hidden ferrimagnetic order unveiled by application of a magnetic field.

View Article: PubMed Central - PubMed

Affiliation: Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA.

ABSTRACT
Magnetoelectric (ME) effect is recognized for its utility for low-power electronic devices. Largest ME coefficients are often associated with phase transitions in which ferroelectricity is induced by magnetic order. Unfortunately, in these systems, large ME response is revealed only upon elaborate poling procedures. These procedures may become unnecessary in single-polar-domain crystals of polar magnets. Here we report giant ME effects in a polar magnet Fe2Mo3O8 at temperatures as high as 60 K. Polarization jumps of 0.3 μC/cm(2), and repeated mutual control of ferroelectric and magnetic moments with differential ME coefficients on the order of 10(4) ps/m are achieved. Importantly, no electric or magnetic poling is needed, as necessary for applications. The sign of the ME coefficients can be switched by changing the applied "bias" magnetic field. The observed effects are associated with a hidden ferrimagnetic order unveiled by application of a magnetic field.

No MeSH data available.


Related in: MedlinePlus

Magnetically-induced electric polarization, and the metemagnetic transition.(a) Temperature dependence of the c-axis dielectric constant ϵ(T), f = 44 kHZ. (b) Variation of the c-axis electric polarization ΔP with temperature. (c,d) Magnetic field dependence of magnetization M(H) and polarization ΔP(H) at various temperatures. In (d), solid (open) circles depict the data obtained upon sweeping the magnetic field up (down).
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f2: Magnetically-induced electric polarization, and the metemagnetic transition.(a) Temperature dependence of the c-axis dielectric constant ϵ(T), f = 44 kHZ. (b) Variation of the c-axis electric polarization ΔP with temperature. (c,d) Magnetic field dependence of magnetization M(H) and polarization ΔP(H) at various temperatures. In (d), solid (open) circles depict the data obtained upon sweeping the magnetic field up (down).

Mentions: The temperature variation of DC magnetic susceptibility χ in zero field-cooled (ZFC) and field-cooled (FC) processes is shown in Fig. 1(e) for the magnetic field both parallel and normal to the c axis. The shapes of the curves are consistent with the transition to the AFM order shown in Fig. 1(c) at TN = 61 K, with Fe2+ spins pointing along the c axis. The large difference between the c-axis and in-pane susceptibilities in the paramagnetic state demonstrates appreciable anisotropy of the Fe2+ spins. No thermal hysteresis is observed, see Supplementary Fig. 1. A large specific heat (CP) anomaly is present at the magnetic transition, see Fig. 1(f). To account for the phonon part, the specific heat was fit to a double Debye model for T > TN (90 to 200 K). The best fit, shown in Fig. 1(f), was obtained for the Debye temperatures θD1 = 174 K and θD2 = 834 K. It fails for T < TN as it implies a negative magnetic contribution for T < 50 K. This indicates an additional lattice contribution for these temperatures, suggesting a structural transition associated with the magnetic order. This suggestion is corroborated by the temperature dependence of the dielectric constant ε(T) and the variation of the electric polarization ΔP(T) ∫ P(T)-P(T = 120 K), both along the c axis, shown in Fig. 2(a,b). In particular, the jump of ΔP at TN clearly indicates simultaneous magnetic and structural transitions. The magnitude of this jump, ~0.3 μC/cm2, is larger than the values typically observed in multiferroics, and is the largest measured value in polar magnets, to our knowledge. Importantly, no poling is needed in an already polar material to observe the changes shown in Fig. 2(a,b). In particular, ΔP was measured by integrating the pyroelectric current on warming after cooling down to T = 5 K in zero electric field (see Supplementary Fig. 2 for details). In our measurements, the direction of the ΔP vector (along or opposite to the positive direction of the c axis defined above) is undetermined. First principles calculations described below indicate that ΔP points in the positive c direction, hence we adopt this convention here.


Unveiling hidden ferrimagnetism and giant magnetoelectricity in polar magnet Fe2Mo3O8.

Wang Y, Pascut GL, Gao B, Tyson TA, Haule K, Kiryukhin V, Cheong SW - Sci Rep (2015)

Magnetically-induced electric polarization, and the metemagnetic transition.(a) Temperature dependence of the c-axis dielectric constant ϵ(T), f = 44 kHZ. (b) Variation of the c-axis electric polarization ΔP with temperature. (c,d) Magnetic field dependence of magnetization M(H) and polarization ΔP(H) at various temperatures. In (d), solid (open) circles depict the data obtained upon sweeping the magnetic field up (down).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4508583&req=5

f2: Magnetically-induced electric polarization, and the metemagnetic transition.(a) Temperature dependence of the c-axis dielectric constant ϵ(T), f = 44 kHZ. (b) Variation of the c-axis electric polarization ΔP with temperature. (c,d) Magnetic field dependence of magnetization M(H) and polarization ΔP(H) at various temperatures. In (d), solid (open) circles depict the data obtained upon sweeping the magnetic field up (down).
Mentions: The temperature variation of DC magnetic susceptibility χ in zero field-cooled (ZFC) and field-cooled (FC) processes is shown in Fig. 1(e) for the magnetic field both parallel and normal to the c axis. The shapes of the curves are consistent with the transition to the AFM order shown in Fig. 1(c) at TN = 61 K, with Fe2+ spins pointing along the c axis. The large difference between the c-axis and in-pane susceptibilities in the paramagnetic state demonstrates appreciable anisotropy of the Fe2+ spins. No thermal hysteresis is observed, see Supplementary Fig. 1. A large specific heat (CP) anomaly is present at the magnetic transition, see Fig. 1(f). To account for the phonon part, the specific heat was fit to a double Debye model for T > TN (90 to 200 K). The best fit, shown in Fig. 1(f), was obtained for the Debye temperatures θD1 = 174 K and θD2 = 834 K. It fails for T < TN as it implies a negative magnetic contribution for T < 50 K. This indicates an additional lattice contribution for these temperatures, suggesting a structural transition associated with the magnetic order. This suggestion is corroborated by the temperature dependence of the dielectric constant ε(T) and the variation of the electric polarization ΔP(T) ∫ P(T)-P(T = 120 K), both along the c axis, shown in Fig. 2(a,b). In particular, the jump of ΔP at TN clearly indicates simultaneous magnetic and structural transitions. The magnitude of this jump, ~0.3 μC/cm2, is larger than the values typically observed in multiferroics, and is the largest measured value in polar magnets, to our knowledge. Importantly, no poling is needed in an already polar material to observe the changes shown in Fig. 2(a,b). In particular, ΔP was measured by integrating the pyroelectric current on warming after cooling down to T = 5 K in zero electric field (see Supplementary Fig. 2 for details). In our measurements, the direction of the ΔP vector (along or opposite to the positive direction of the c axis defined above) is undetermined. First principles calculations described below indicate that ΔP points in the positive c direction, hence we adopt this convention here.

Bottom Line: Magnetoelectric (ME) effect is recognized for its utility for low-power electronic devices.Largest ME coefficients are often associated with phase transitions in which ferroelectricity is induced by magnetic order.The observed effects are associated with a hidden ferrimagnetic order unveiled by application of a magnetic field.

View Article: PubMed Central - PubMed

Affiliation: Rutgers Center for Emergent Materials and Department of Physics and Astronomy, Rutgers University, Piscataway, New Jersey 08854, USA.

ABSTRACT
Magnetoelectric (ME) effect is recognized for its utility for low-power electronic devices. Largest ME coefficients are often associated with phase transitions in which ferroelectricity is induced by magnetic order. Unfortunately, in these systems, large ME response is revealed only upon elaborate poling procedures. These procedures may become unnecessary in single-polar-domain crystals of polar magnets. Here we report giant ME effects in a polar magnet Fe2Mo3O8 at temperatures as high as 60 K. Polarization jumps of 0.3 μC/cm(2), and repeated mutual control of ferroelectric and magnetic moments with differential ME coefficients on the order of 10(4) ps/m are achieved. Importantly, no electric or magnetic poling is needed, as necessary for applications. The sign of the ME coefficients can be switched by changing the applied "bias" magnetic field. The observed effects are associated with a hidden ferrimagnetic order unveiled by application of a magnetic field.

No MeSH data available.


Related in: MedlinePlus