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論文

Role of magnetic chirality in polarization flip upon a commensurate-incommensurate magnetic phase transition in YMn$$_{2}$$O$$_{5}$$

脇本 秀一; 木村 宏之*; 坂本 勇馬*; 福永 守*; 野田 幸男*; 武田 全康; 加倉井 和久

Physical Review B, 88(14), p.140403_1 - 140403_5, 2013/10

https://doi.org/10.1103/PhysRevB.88.140403
 被引用回数：18 パーセンタイル：60.99(Materials Science, Multidisciplinary)

We have performed simultaneous measurements of magnetic chirality by using polarized neutrons and electric polarization along the $$b$$-axis of single crystals of YMn$$^{4+}$$(Mn$$_{1-x}$$Ga$$_{x}$$)$$^{3+}$$O$$_{5}$$ with $$x=0.047$$ and $$0.12$$, in which nonmagnetic Ga-ions dilute Mn$$^{3+}$$ spins. Measurements conducted under zero field heating after various field-cooling conditions evidence that the magnetic chirality of Mn$$^{4+}$$ cycloidal spins plays a dominant role in the incommensurate magnetic (ICM) phase, whereas the magnetic exchange striction by the Mn$$^{4+}$$-Mn$$^{3+}$$ chain plays a dominant role in the commensurate magnetic (CM) phase. The polarization of YMn$$_{2}$$O$$_{5}$$ flips upon CM to ICM phase transition because the ferroelectricity driven by the magnetic chirality and the exchange striction provides opposite directions of polarization.

論文

Magnetic-field-induced polarization flop in multiferroic TmMn$$_{2}$$O$$_{5}$$

福永 守*; 坂本 勇馬*; 木村 宏之*; 野田 幸男*; 阿部 伸行*; 谷口 耕治*; 有馬 孝尚*; 脇本 秀一; 武田 全康; 加倉井 和久; et al.

Physical Review Letters, 103(7), p.077204_1 - 077204_4, 2009/08

https://doi.org/10.1103/PhysRevLett.103.077204
 被引用回数：49 パーセンタイル：86.08(Physics, Multidisciplinary)

We discovered a reversible electric polarization flop from the $$a$$ axis ($$P_a$$) to the $$b$$ axis ($$P_b$$) in multiferroic TmMn$$_{2}$$O$$_{5}$$ below 5 K by applying a magnetic field of approximately 0.5 T along the $$c$$ axis. This phenomenon is the first example of the rare-earth ($$R$$) compound $$R$$Mn$$_{2}$$O$$_{5}$$. This magnetic-field-induced polarization flop corresponds to a magnetic phase transition from one incommensurate magnetic (ICM) $$P_a$$ phase to another ICM $$P_b$$ phase, which is equivalent to an ICM $$P_b$$ phase above 5 K under no magnetic field. The spin chirality in the $$bc$$ plane, which was observed in the $$P_b$$ phase by polarized neutron diffraction, disappeared in the ICM $$P_a$$ phase. This indicates that the polarization in the ICM phases of TmMn$$_2$$O$$_5$$ was induced by an $$S_i times S_j$$ type interaction.

口頭

Ga置換したYMn$$^{4+}$$(Mn$$_{1-x}$$Ga$$_{x}$$)$$^{3+}$$O$$_{5}$$の磁気カイラリティと電気分極

脇本 秀一; 加倉井 和久; 坂本 勇馬*; 福永 守*; 木村 宏之*; 野田 幸男*

no journal, , 

マルチフェロイック物質RMn$$_{2}$$O$$_{5}$$の電気磁気効果の起源として、Mn$$^{4+}$$スピンのサイクロイドスピン構造に起因するS$$times$$S機構と、Mn$$^{3+}$$鎖とMn$$^{4+}$$鎖間の磁気相関に由来するexchange striction (S$$cdot$$S)機構が指摘されている。本研究では、YMn$$_{2}$$O$$_{5}$$のMn$$^{3+}$$を非磁性Ga$$^{3+}$$イオンに置換することでS$$cdot$$Sの影響を希釈し、JRR-3のTAS-1の偏極中性子でS$$times$$Sを観測してその効果を検証した。その結果、強誘電相の格子整合磁気秩序相ではS$$cdot$$S機構が強く、強誘電相の弱まる格子不整合磁気秩序相ではS$$times$$S機構が強く寄与することを明らかにした。

口頭

YMn$$^{4+}$$(Mn$$_{1-x}$$Ga$$_{x}$$)$$^{3+}$$O$$_{5}$$におけるスピンカイラリティと分極

脇本 秀一; 木村 宏之*; 福永 守*; 坂本 勇馬*; 加倉井 和久; 野田 幸男*

no journal, , 

マルチフェロイック物質であるRMn$$_{2}$$O$$_{5}$$は、Mn$$^{4+}$$スピンのサイクロイドスピン構造に起因するS$$times$$S機構と、Mn$$^{3+}$$鎖とMn$$^{4+}$$鎖間の磁気相関に由来するexchange striction (S・S)機構が指摘されている。本研究では、YMn$$_{2}$$O$$_{5}$$のMn$$^{3+}$$を非磁性Ga$$^{3+}$$イオンに置換することでS・Sの影響を希釈し、JRR-3のTAS1の偏極中性子でS$$times$$Sを観測してその効果を検証した。結果、低温の格子非整合磁気秩序相においてはS$$times$$S機構が強く、高温の格子整合磁気秩序相ではS・S機構が強いことが明らかとなった。

口頭

Magnetic chirality and electric polarization in multiferroic YMn$$_{2}$$O$$_{5}$$

脇本 秀一; 木村 宏之*; 福永 守*; 坂本 勇馬*; 野田 幸男*; 加倉井 和久

no journal, , 

There are two candidates of the origin of the magnetic-driven ferroelectricity in YMn$$_{2}$$O$$_{5}$$, one is the $$S$$$$times$$$$S$$ model and the other is the $$S$$$$cdot$$$$S$$ model. We have measured spin chirality and polarization of YMn$$^{4+}$$(Mn$$_{1-x}$$Ga$$_{x}$$)$$^{3+}$$O$$_{5}$$ where non-magnetic Ga ions dilute the $$S$$$$cdot$$$$S$$ contribution. We have succeeded to separate these two contributions, and found that the $$S$$$$times$$$$S$$ mechanism is dominant in the low-temperature phase while the $$S$$$$cdot$$$$S$$ mechanism is dominant in the intermediate temperature phase.

口頭

Magnetic chirality and electric polarization in $$R$$Mn$$_2$$O$$_5$$

脇本 秀一; 木村 宏之*; 福永 守*; 坂本 勇馬*; 野田 幸男*; 加倉井 和久

no journal, , 

$$R$$Mn$$_2$$O$$_5$$ is a multiferroic compound in which ferroelectricity is driven by magnetism. So far two models have been proposed to explain spin-driven ferroelectriciry in this compound, $$S times S$$ and $$S cdot S$$ models. By detailed investigation of magnetic chirality by polarized neutron diffraction, we have succeeded to distinguish these two contributions to the ferroelectric polarization. We conclude that the $$S cdot S$$ mechanism is dominant in the commensurate phase and the $$S times S$$ mechanism is dominant in the low temperature incommensurate phase.

口頭

A Role of the magnetic chirality in polarization flip in YMn$$_2$$O$$_5$$

脇本 秀一; 木村 宏之*; 福永 守*; 坂本 勇馬*; 武田 全康; 加倉井 和久; 野田 幸男*

no journal, , 

A multiferroic compound YMn$$_2$$O$$_5$$ shows characteristic dielectric polarization flip upon the magnetic phase transition from commensurate magnetic (CM) to low-temperature incommensurate magnetic (LTICM) phases. By utilizing simultaneous measurements of dielectric polarization and magnetic chirality by polarized neutron diffraction, we have studied the direct relation between them. We have identified that $$S cdot S$$ and $$S times S$$, two major mechanisms of spin-driven ferroelectricity, are dominant in the CM and LTICM phases, respectively, and concluded that a conservation of magnetic chirality gives rise to the polarization flip upon the CN-LTICM transition.

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