Study On Anomalous Nernst Effect Of Fe-based Thin Films

With the development of science and technology,energy consumption rises constantly during the past decades and the energy shortage has become the focus of the world.Thermoelectric(TE)materials have attracted a lot of attention of the academic and industrial circles because of their ability to directly convert electrical energy and thermal energy.TE materials has been used as thermometers,generators,and coolers.The(anomalous)Nernst effect is another thermoelectric effect,which can achieve high-efficiency thermoelectric conversion.In this thesis,for testing the anomalous Nernst voltage signal of the samples,we first made a set of measurement devices.The tests on the temperature difference and the magnetic field are verified show that our self-built anomalous Nernst voltage device can generate stable temperature difference and magnetic field,and has good repeatability.Especially,as the heating voltage is 3V,we can get the most stable temperature difference and therefore,in the following tests,3V heating-voltage is chosen.In this thesis,we prepared Fe films on Si substrates by the magnetron sputtering method and explored the influence of film thickness on the anomalous Nernst effect.The research result shows that the anomalous Nernst voltage decreases continuously with increasing of the Fe thin film sample thickness.When the thickness of the film increases to more than 50 nm,the anomalous Nernst voltage tends to be unchanged.The effects of the geometry of Fe film samples on the anomalous Nernst effect also are considered.We found that under a certain temperature difference,the anomalous Nernst voltage generated by the device is proportional to the width-to-length ratio.This might guide the the design of anomalous Nernst devices.Due to the very weak voltage signal on Fe films,we next investigate the anomalous Nernst effect of the FeCoNi alloy films and analyze the corresponding effects of the atomic ratio in the films.The results show that the anomalous Nernst voltage signal and transverse Seebeck coefficient of FeCoNi alloy film are larger than Fe Co alloy film and Ni film,which might be caused by the larger saturation magnetization of FeCoNi alloy film.We also changed the sputtering power of Ni target to adjust the element amount in FeCoNi alloy film and found that the anomalous Nernst voltage signal increases firstly and then decreases quickly as Ni content increases.