Free spectral range magnetic tuning of an integrated microcavity

Tunable whispering-gallery-mode(WGM)microcavities are promising devices for reconfigurable photonic applications such as widely tunable integrated lasers and reconfigurable optical filters for optical communication and information processing.Scaling up these devices demands the ability to tune the optical resonances in an integrated manner over a full free spectral range(FSR).Here we propose a high-speed full FSR magnetic tuning scheme of an integrated silicon nitride(Si_(3)N_(4))double-disk microcavity.By coating a magnetostrictive film on the spokes and the central pad of the Si_(3)N_(4) cavity,magnetic tuning can be realized using a microcoil integrated on the same chip.An FSR tuning can be achieved by combining magnetostrictive strain with strong optomechanical interactions provided by the double-disk microcavity.We calculate the required magnetic flux density to tune an FSR(B_(FSR))as a function of several key geometric parameters,including the air gap,radius,width of the spokes and ring of the double-disk cavities,as well as the thickness of the magnetostrictive film.The proposed structure enables a full FSR tuning with a required magnetic flux density of milli-Tesla(mT)level.We also study the dynamic response of the integrated device with an alternating current(AC)magnetic field driving,and find that the tuning speed can reach hundreds of kHz in the air.

Pressure Tuning of Magnetism and Drastic Increment of Thermal Conductivity under Applied Magnetic Field in HgCr_2S_4

HgCr2S4 is a typical compound manifesting competing ferromagnetic （FM） and antiferromagnetic （AFM） exchanges as well as strong spin-lattice coupling. Here we study these effects by intentionally choosing a combination of magnetization under external hydrostatic pressure and thermal conductivity at various magnetic fields. Upon applying pressure up to 10 kbar at 1 kOe, while the magnitude of magnetization reduces progressively, the AFM ordering temperature TN enhances concomitantly at a rate of about 1.5 K/kbar. Strikingly, at lO kOe the field polarized FM state is found to be driven readily back to an AFM one even at only 5kbar. In addition, the thermal conductivity exhibits drastic increments at various fields in the temperature range with strong spin fluctuations, reaching about 30% at 50 kOe. Consequently, the results give new experimental evidence of spin-lattice coupling. Apart from the colossal magnetoeapacitance and colossal magnetoresistance reported previously, the findings here may enable new promising functionalities for potential applications.

Spin-polarized oscillations of conductance through an Aharonov-Casher ring with a quantum gate

Spin-polarized oscillations in conductance is studied through a mesoscopic Aharonov-Casher （AC） ring with a quantum gate that is tuned by an external magnetic field. Both the conductance and its spin polarization at zero temperature are calculated as a function of the textured electric field, the magnetic field, and Fermi energy. It is found that for some special Fermi energies, spin-up electrons are driven into perfect transmission or reflection states, unaffected by the electric field when Zeeman energy of the incident electrons aligns with one level of the isolated stub or is larger than Fermi energy. This brings about AC oscillations of spin-down conductance. It shows that periodic oscillations of the conductance appear in the adiabatic region of quantum phase and in the normdiabatic region. Anomalous behavior of the conductance oscillation is dependent on the difference between the tilt angle of spin and the electric field.

Optical fiber-based magnetically-tuned graphene mechanical resonator

In this study,an optical fiber-based magnetically-tuned graphene mechanical resonator(GMR)is demonstrated by integrating superparamagnetic iron oxide nanoparticles on the graphene membrane.The resonance frequency shift is achieved by tuning the tension of the graphene membrane with a magnetic field.A resonance frequency tunability of 23 kHz using a 100 mT magnetic field is achieved.The device provides a new way to tune a GMR with a non-contact force.It could also be used for weak magnetic field detection in the future with further improvements in sensitivity.

Strain-sensitive ferromagnetic two-dimensional Cr_(2)Te_(3)

Searching for room temperature magnetic two-dimensional(2D)materials is a charming goal,but the number of satisfied materials is tiny.Strain can introduce considerable deformation into the lattice structure of 2D materials,and thus significantly modulate their intrinsic properties.In this work,we demonstrated a remarkable strain-modulated magnetic properties in the chemical vapor deposited Cr_(2)Te_(3) nanoflakes grown on mica substrate.We found the Curie temperature of Cr_(2)Te_(3) nanoflakes can be positively and negatively modulated under tensile and compressive strain respectively,with a maximum varied value of -40 and-90 K,dependent on the thickness of samples.Besides,the coercive field of Cr_(2)Te_(3) nanoflakes also showed a significant decrease under the applied strain,suggesting the decrease of exchange interaction or the change of the magnetization direction.This work suggests a promise to employ interfacial strain to accelerate the practical application of room temperature 2D magnetics.

Typical dampers and energy harvesters based on characteristics of ferrofluids

Ferrofluids are a type of nanometer-scale functional material with fluidity and superparamagnetism.They are composed of ferromagnetic particles,surfactants,and base liquids.The main characteristics of ferrofluids include magnetization,the magnetoviscous effect,and levitation characteristics.There are many mature commercial ferrofluid damping applications based on these characteristics that are widely used in numerous fields.Furthermore,some ferrofluid damping studies such as those related to vibration energy harvesters and biomedical devices are still in the laboratory stage.This review paper summarizes typical ferrofluid dampers and energy harvesting systems from the 1960s to the present,including ferrofluid viscous dampers,ferrofluid inertia dampers,tuned magnetic fluid dampers(TMFDs),and vibration energy harvesters.In particular,it focuses on TMFDs and vibration energy harvesters because they have been the hottest research topics in the ferrofluid damping field in recent years.This review also proposes a novel magnetic fluid damper that achieves energy conversion and improves the efficiency of vibration attenuation.Finally,we discuss the potential challenges and development of ferrofluid damping in future research.