Magnetic Anisotropy of Single Crystals of NiO and MnO

Uchida, Enji; Fukuoka, Nobuo; Kondoh, Hisamoto; Takeda, Tadao; Nakazumi, Yoshihide; Nagamiya, Takeo

doi:10.1143/jpsj.23.1197

Cited by 35 publications

(13 citation statements)

References 13 publications

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“…14 shows that a field of Ͼ2 kOe along ͓110͔ may be used to align the spin axes along ͓112͔. When the field reaches 5 kOe, a single S domain is obtained, 14 but the T-domain wall starts to move. 13 Considering these facts, magnetic field of 4.5 kOe was applied parallel to ͓110͔ during the measurements.…”

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confidence: 99%

“…The measurements were achieved at RT ͓ϳ300 K ͑ϽT N ͔͒ to prevent introducing a new domain caused by tiny stresses or thermal gradients. 13,14 We also performed similar measurements under 1.7 kOe at some phonon vectors to study field-induced effects, such as magnetoelectric effects. The results show the same phonon peak positions as at 4.5 kOe, within an experimental accuracy of Ϯ0.3 meV.…”

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confidence: 99%

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Effects of anisotropic charge on transverse optical phonons in NiO: Inelastic x-ray scattering spectroscopy study

2010

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Phonon dispersion of detwinned NiO is measured using inelastic x-ray scattering. It is found that, near the zone center, the energy of the transverse-optical-phonon mode polarized parallel to the antiferromagnetic order is ϳ1 meV lower than that of the mode polarized perpendicular to the order, at room temperature. This is explained via anisotropic polarization of the Ni and O atoms, as confirmed using a Berry's phase approach with first-principles calculations. Our explanation avoids an apparent contradiction in previous discussions focusing on Heisenberg interaction.Transition-metal mono-oxides are fundamental materials for studying properties of magnetic and strongly correlated systems. Among them, NiO and MnO are antiferromagnetic ͑AFM͒ insulators with similar crystal structure and physical properties. The AFM order and lattice contraction occur along the ͓111͔ direction below the Néel temperature ͑T N = 523 K for NiO͒. The order consists of ferromagnetic ͑111͒ planes. Above T N , both have a rocksalt structure. NiO and MnO are relatively simple, because they have nondegenerate electronic ground states, and are free from Jahn-Teller effects, unlike FeO and CoO. 1 The magnetism of these materials is often discussed in terms of a superexchange mechanism. MnO has antiferromagnetic interactions both in the nearest-neighbor ͑J 1 ͒ and next-nearest-neighbor ͑J 2 ͒ exchanges, and these interactions reproduce the experimental results. 2,3 On the other hand, J 1 for NiO still remains uncertain, perhaps because it is much smaller than the antiferromagnetic superexchange J 2 interaction, which is responsible for the AFM order. For example, local spin-density approximation ͑LSDA͒ + U calculations give ferromagnetic J 1 ͑Ref. 3͒ while some calculations such as GW show antiferromagnetic J 1 . 4 Experimentally, a measurement of spin-wave dispersion indicates ferromagnetic J 1 ͑Ref. 5͒ while one of magnetic susceptibility suggests antiferromagnetic J 1 . 6 Another issue is that LSDA+ U calculation results are not easily reconciled with the exchange-interaction picture of NiO. According to Refs. 2 and 7, the lattice distortion is dominated by J 1 with no contribution from J 2 , and antiferromagnetic J 1 causes the contraction in ͓111͔, if ͉J 1 ͉ decreases with increasing the distance between the nearest-neighbor Ni atoms. Based on this discussion, the calculated ferromagnetic J 1 ͑Ref. 3͒ is not consistent with the calculated 8 ͑and observed͒ contraction in NiO, suggesting an additional ingredient is needed to understand the calculation results.The energy of transverse optical ͑TO͒ phonons can be used as a direct probe of microscopic coupling; 9 TO modes that would be degenerate in a cubic rocksalt structure, are split at the zone center under the AFM order, with the energy of the mode polarized along the order ͑E ʈ TO ͒ different than that of the mode polarized in the plane perpendicular to the order ͑E Ќ TO ͒. As discussed in Ref. 3 the sign of this difference ͑E ʈ TO − E Ќ TO ͒ can be linked to the sign of J 1 . The pict...

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Effects of anisotropic charge on transverse optical phonons in NiO: Inelastic x-ray scattering spectroscopy study

2010

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“…40 Combining the magnetic torque data obtained in the (001) and (111) plane of single-crystalline NiO 26 with the anisotropy constant obtained through the spin-flop field in the (111) plane 40 , we estimate the anisotropy constant in the (001) plane is K = 5.25 ergs/g. Substituting the parameters in Eq.…”

Section: B Biaxial Afi Nio and Coomentioning

confidence: 89%

Antiferromagnetic anisotropy determination by spin Hall magnetoresistance

Wang

Hou

Qiu

et al. 2017

Journal of Applied Physics

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An electric method for measuring magnetic anisotropy in antiferromagnetic insulators (AFI) is proposed. When a metallic film with strong spin-orbit interaction, e.g. platinum (Pt), is deposited on an AFI, its resistance should be affected by the direction of the AFI Néel vector due to the spin Hall magnetoresistance (SMR). Accordingly, the direction of the AFI Néel vector, which is affected by both the external magnetic field and the magnetic anisotropy, is reflected in resistance of Pt. The magnetic field angle dependence of the resistance of Pt on AFI is calculated by considering the SMR, which indicates that the antiferromagnetic anisotropy can be obtained experimentally by monitoring the Pt resistance in strong magnetic fields. Calculations are performed for realistic systems such as Pt/Cr2O3, Pt/NiO and Pt/CoO.

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“…The strongly axially distorted bulk antiferromagnets NiO, MnO and CoO contain a few magnetic domains only and have onedimensional dynamic symmetry. By application of moderate external pressure or a magnetic field it is possible to transform these magnets into the single domain state [51].…”

Section: Discussionmentioning

confidence: 99%