Magnetic field dependence of antiferromagnetic resonance in NiO

Abstract

We report on measurements of magnetic field and temperature dependence of antiferromagnetic resonances in the prototypical antiferromagnet NiO. The frequencies of the magnetic resonances in the vicinity of 1 THz have been determined in the time-domain via time-resolved Faraday measurements after selective excitation by narrow-band superradiant terahertz (THz) pulses at temperatures down to 3 K and in magnetic fields up to 10 T. The measurements reveal two antiferromagnetic resonance modes, which can be distinguished by their characteristic magnetic field dependencies. The nature of the two modes is discussed by comparison to an eight-sublattice antiferromagnetic model, which includes superexchange between the next-nearest-neighbor Ni spins, magnetic dipolar interactions, cubic magnetocrystalline anisotropy, and Zeeman interaction with the external magnetic field. Our study indicates that a two-sublattice model is insufficient for the description of spin dynamics in NiO, while the magnetic-dipolar interactions and magnetocrystalline anisotropy play important roles.

Magnetic resonance induced pseudoelectric field and giant current response in axion insulators

“…In the following, we consider an even number of layers of MnBi 2 Te 4 films so that the top and bottom layers have anti-parallel magnetization. To describe the magnetic dynamics of AFM in MnBi 2 Te 4 , particularly around the AFMR, the exchange interaction of magnetization be-tween the neighboring layers should be included in the LLG equation and leads to a larger resonance frequency ω 1 ∼THz [45][46][47]. Since 0.1eV h(1THz)≈ 4meV, the adiabatic approximation is still valid and Eq.…”

Ultrafast manipulation of the NiO antiferromagnetic order via sub-gap optical excitation

“…This frequency is close to the eigenfrequency of the out-of-plane magnon mode, which has been extensively studied in both optical and THz Please do not adjust margins Please do not adjust margins spectroscopy measurements. 14,19,[41][42][43][44][45][46][47][48][49] There are two magnon eigenmodes: in-plane and out-of-plane modes. For the in-plane mode, the AFM vector between two adjacent ferromagnetic planes is modulated along the [1-10] direction, which lies in the (111) plane.…”

“…[111] direction), the out-of-plane mode has a much higher eigenfrequency than the in-plane mode. Both of these two magnon modes are excitable by ultrashort optical laser pulses and have been detected at around 0.14 THz 20, 46 and 1.07 THz 20,42,[45][46][47]49 for the in-plane mode and the out-of-plane mode, respectively. The mode also displays a temperature dependence with a frequency reduction as the Néel temperature is approached.…”

Broadband and narrowband laser-based terahertz source and its application for resonant and non-resonant excitation of antiferromagnetic modes in NiO

“…The magnetic field of the THz pulse was applied parallel to the (111) surface of the NiO sample and had direct access to the degrees of freedom of the spin system of the antiferromagnetic. In this case, a Zeeman torque is created on the magnetic dipole associated with each spin at a frequency that can be tuned in resonance with the collective mode of the NiO magnons [27][28][29][30].…”

“…In [28], the presence of local maxima at 0.77 and 1.23 THz was interpreted as the process of mixing the difference and sum frequencies of magnon oscillations in the plane and outside the plane with a frequency of 0.23 and 1 THz. In our experiment, we assume that the appearance of local maxima is not related to the propagation effect (∆f = 0.14 THz not 0.25 THz), but may be due to splitting of the resonant mode of 1 THz in the magnetic field of the THz pulse, by analogy with [30,34].…”