Observation Of Emergent Particles In Magnets Using Nitrogen-vacancy Color Centers In Diamond

Studying properties of particles is fundamental in exploring nature and physics.Apart from material particles,emergent particles in condensed matter physics play an important role in various phenomenon in solid materials.There are spin-related emer-gent particles in magnetic materials.Magnetic skyrmions are particle-like spin textures of nontrivial topology found in recent years.It can induce topological effects and has potential applications in spintronics.As elementary excitation in magnets,magnons exhibit abundant behaviors and are fundamental blocks in the promising magnonics.Therefore,magnons attract wide attention all the time.Recently,sensing technology based on quantum objects has been developed.These technologies have accomplished precise detection beyond classical methods.Acting as a single spin,nitrogen-vacancy color centers(NV centers)are highly sensitive and high-resolution magnetometer.NV center-based magnetic imaging combined with scanning probe microscopy has shown advantages in researches of condensed matter physics and become a powerful tool in studying nanomagnetism.In addition,NV centers can detect microwave of GHz and thus measure properties of magnons.NV center magnetome-ters fit prettily with these emergent particles in magnets.Therefore,diamond sensors have unique advantages in observation of these particles.This thesis would introduce sensing technology based on NV centers in diamond,studying the structure of mag-netic skyrmions using this technology,and measurements of spin wave spectrums and magnon temperature.Magnetization direction reverses in the nanoscale skyrmion,which would generate stray fields with large fluctuation.To resolve the difficulty in imaging large-gradient magnetic fields using NV centers,a tracking method and a reconstruction algorithm are designed.Simulations and experiments prove that this scanning approach can realize fast imaging of large-gradient magnetic fields.Determination of structure is important in studies of magnetic skyrmions.Micro-magnetism and magnetic imaging based on NV centers can be combined to address this issue.A kind of biskyrmions with undetermined structure has been studied in this the-sis.Micromagnetism simulations show that biskyrmions observed with Lorentz trans-mission electron microscope can be explained by type-2 bubbles in magnets with tilt magnetic anisotropy.In addition,signs of magnetic bubbles have been found in thin film or bulk magnets using NV center magnetic microscopy.NV centers are able to measure spin wave or magnon in several ways.Thus,dif-ferent measurement methods can be applied to meet needs.In the measurement of spin wave spectrums of skyrmions,off-resonance method acquires response of the magnet driven by microwave.On the other hand,NV centers can extract statistic information of fluctuation magnons as relaxometry.Magnons' temperature is measured with NV cen-ter relaxometry in experiments.NV centers can detect the phenomenon that magnons and phonons may have different temperature in the magnet under temperature gradient.