A ferromagnetic metal consists of localized electrons and conduction electrons coupled through strong exchange interaction. Together, these localized electrons contribute to the magnetization of the system, while conduction electrons lead to the formation of spin and charge current. Femtosecond out of equilibrium photoexcitation of ferromagnetic thin films generates a transient spin current at ultrafast timescales that have opened a route to probe magnetism offered by the conduction electrons. In the presence of a neighboring heavy metal layer, the non-equilibrium spin current is converted into a pulsed charge current and gives rise to terahertz (THz) emission. Here, we propose and demonstrate a tool known as the terahertz spintronic magnetometry. The hysteresis loop obtained by sweeping terahertz (THz) pulse amplitude as a function of the magnetic field is in excellent agreement with the vibrating-sample magnetometer measurements. Furthermore, a modified transfer-matrix method employed to model the THz propagation within the heterostructure theoretically elucidates a linear relationship between the THz pulse amplitude and sample magnetization. The strong correlation, thus, reveals spintronic terahertz emission as an ultrafast magnetometry tool with reliable in-plane magnetization detection, highlighting its technological importance in the characterization of ferromagnetic thin-films through terahertz spintronic emission spectroscopy.
Heated atomic force microscope (AFM) nanoprobe is an attractive instrument for highly local thermal processing. The gases between the nanoprobe and the sample surface exhibit different behaviors from the macroscopic gases due to the nanoscale probe-sample distance. In this paper, the thermal conduction of rarefied gases heated by an AFM nanoprobe is investigated by means of the direct simulation Monte Carlo method. The heat reservoir of AFM nanoprobe consists of a heater platform and a nanotip. The effects of heater platform and nanotip on the gas heat transfer are analyzed. It is found that both the size of heater platform and the geometry of nanotip have noticeable influence on the heat flux density distribution and the spatial resolution on the sample surface. The results show that a spatial resolution of a few tens of nanometers can be achieved by the hot AFM nanoprobe and the power provided to the spatial scale can be at an order of 10−8 W. It is also found that a sample surface can be efficiently heated locally without the contact of the nanoprobe and sample, thus alleviating the wear between them and improving the system reliability. The work provides an insight for rational design and optimization of the heated nanoprobe/surface configuration-based systems for topography applications.
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