Direct observation of spin-quadrupolar excitations in 
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 by high-field electron spin resonance

Akaki, Mitsuru; Yoshizawa, Daichi; Okutani, Akira; Kida, Takanori; Romhányi, Judit; Penc, Karlo; Hagiwara, Masayuki

doi:10.1103/physrevb.96.214406

Cited by 23 publications

(16 citation statements)

References 56 publications

(132 reference statements)

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“…The instability of the magnetic state with zero electric polarization indicates the role of polarization-polarization coupling, which can be expressed also in terms of spin nematic or spin quadrupolar interactions. Indeed, the relevance of such fourth-order spin interactions has been predicted theoretically [37] and confirmed experimentally [21,38] [13]). The large difference between the in-plane and outof-plane saturation fields together with the weak susceptibility anisotropy in low magnetic fields may imply that the tetragonal anisotropy in Ca 2 CoSi 2 O 7 is not weak but has different anisotropy terms, such as the single-ion anostropy, exchange anisotropy and g-factor anisotropy, which compete and nearly compensate each other in the low-field magnetic state.…”

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confidence: 75%

Magnetic structure of the magnetoelectric material Ca2CoSi2O7

et al. 2017

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Detailed investigation of Ca 2 CoSi 2 O 7 was performed in its low-temperature magnetoelectric state combining neutron diffraction with magnetization measurements on single crystals. The crystal and magnetic structures well below the antiferromagnetic transition temperature of T N ≈ 5.7 K were determined using neutron diffraction. Neutron diffraction data imply no structural phase transition from 10 K down to 2.5 K and are well described within the orthorhombic space group P 2 1 2 1 2 with a 3 × 3 × 1 supercell compared with the high-temperature unmodulated state (tetragonal space group P42 1 m). We found that in zero magnetic field the magnetic space group is P 2 1 2 1 2 with antiferromagnetic order along the [100] or [010] axes for two types of 90• twin domains, while neighboring spins along the [001] axis are ordered ferromagnetically. A noncollinear spin arrangement due to small canting within the ab plane is allowed by symmetry and leads to the existence of the tiny spontaneous magnetization below T N . The ordered moment with a magnitude of about 2.8 μ B /Co 2+ at 2.5 K lies in the ab plane. Distinct differences between the magnetic structure of Ca 2 CoSi 2 O 7 as compared to those of Ba 2 CoGe 2 O 7 and Sr 2 CoSi 2 O 7 are discussed.

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confidence: 75%

Magnetic structure of the magnetoelectric material Ca2CoSi2O7

et al. 2017

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“…Though we restricted ourselves to the cases of weak anisotropic interactions in this paper, it is also interesting to investigate cases governed by a large anisotropic interaction such as the case of Ref. [48]. While the formula of the frequency shift [Eq.…”

Section: Discussionmentioning

confidence: 99%

“…[47], various quantities related to ESR are naturally coupled to quadrupole operators and thus ESR is a promising way for detecting the hidden spin nematic order. In ESR experiments, bound triplon-pair modes were observed in the spin gapped phase of the orthogonal dimer spin system SrCu 2 (BO 3 ) 2 [29] and a bound magnon-pair mode was also in the fully polarized phase of Sr 2 CoGe 2 O 7 [48]. Bound magnon pairs can give the instability to the spin nematic ordering when they close the energy gap [5].…”

Section: Introductionmentioning

confidence: 97%

Electron spin resonance for the detection of long-range spin nematic order

Furuya

Momoi

2018

Phys. Rev. B

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Spin nematic phase is a quantum magnetic phase characterized by a quadrupolar order parameter. Since the quadrupole operators are directly coupled to neither the magnetic field nor the neutron, currently, it is an important issue to develop a method for detecting the long-range spin nematic order. In this paper we propose that electron spin resonance (ESR) measurements enable us to detect the long-range spin nematic order. We show that the frequency of the paramagnetic resonance peak in the ESR spectrum is shifted by the ferroquadrupolar order parameter together with other quantities. The ferroquadrupolar order parameter is extractable from the angular dependence of the frequency shift. In contrast, the antiferroquadrupolar order parameter is usually invisible in the frequency shift. Instead, the long-range antiferroquadrupolar order yields a characteristic resonance peak in the ESR spectrum, which we call a magnon-pair resonance peak. This resonance corresponds to the excitation of the bound magnon pair at the wave vector k = 0. Reflecting the condensation of bound magnon pairs, the field dependence of the magnon-pair resonance frequency shows a singular upturn at the saturation field. Moreover, the intensity of the magnon-pair resonance peak shows a characteristic angular dependence and it vanishes when the magnetic field is parallel to one of the axes that diagonalize the weak anisotropic interactions. We confirm these general properties of the magnon-pair resonance peak in the spin nematic phase by studying an S = 1 bilinearbiquadratic model on the square lattice in the linear flavor-wave approximation. In addition, we argue applications to the S = 1/2 frustrated ferromagnets and also the S = 1/2 orthogonal dimer spin system SrCu2(BO3)2, both of which are candidate materials of spin nematics. Our theory for the antiferroquadrupolar ordered phase is consistent with many features of the magnon-pair resonance peak experimentally observed in the low-magnetization regime of SrCu2(BO3)2. arXiv:1707.08784v2 [cond-mat.str-el]

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“…It is worth noting, that the perpendicular components P ⊥1 and P ⊥2 change the S quantum number by ±1, creating dipolar spin excitation, but P chiral changes by ±2, creating quadrupolar spin excitation. 28 None of the components of P transforms according to the fully symmetric irreducible representation A + , Table III. Therefore the expectation value for the static polarization is zero in the ground state.…”

Section: Magneto-chiral Dichroism (Chiral Case): ϕ =mentioning

confidence: 99%

Directional dichroism in the paramagnetic state of multiferroics: A case study of infrared light absorption in Sr2CoSi2O7 at high temperatures

et al. 2019

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The coexisting magnetic and ferroelectric orders in multiferroic materials give rise to a handful of novel magnetoelectric phenomena, such as the absorption difference for the opposite propagation directions of light called the non-reciprocal directional dichroism (NDD). Usually these effects are restricted to low temperature, where the multiferroic phase develops. In this paper we report the observation of NDD in the paramagnetic phase of Sr2CoSi2O7 up to temperatures more than ten times higher than its Néel temperature (7 K) and in fields up to 30 T. The magnetically induced polarization and NDD in the disordered paramagnetic phase is readily explained by the singleion spin-dependent hybridization mechanism, which does not necessitate correlation effects between magnetic ions. The Sr2CoSi2O7 provides an ideal system for a theoretical case study, demonstrating the concept of magnetoelectric spin excitations in a paramagnet via analytical as well as numerical approaches. We applied exact diagonalization of a spin cluster to map out the temperature and field dependence of the spin excitations, as well as symmetry arguments of the single ion and lattice problem to get the spectrum and selection rules. arXiv:1809.10207v1 [cond-mat.str-el]

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Direct observation of spin-quadrupolar excitations in Sr2CoGe2O7 by high-field electron spin resonance

Cited by 23 publications

References 56 publications

Magnetic structure of the magnetoelectric material Ca2CoSi2O7

Magnetic structure of the magnetoelectric material Ca2CoSi2O7

Electron spin resonance for the detection of long-range spin nematic order

Directional dichroism in the paramagnetic state of multiferroics: A case study of infrared light absorption in Sr2CoSi2O7 at high temperatures

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