Magnetic Properties Of Potassium-and Rubidium-Doped Phenylnaphthalene And Phenylquinoline-Like Molecules

The doping of organic aromatic hydrocarbons with alkali metals is an important research direction in physics,materials science and chemistry in recent years,and new organic molecular magnets and organic superconductors have been discovered in these systems.In this paper,doping experiments with potassium and rubidium are carried out on some mixed aromatic hydrocarbons combining fused and non-fused rings by solid-phase synthesis method,and stable molecular crystals are successfully synthesized,and the physical properties of some samples are thoroughly investigated.We have mainly characterized nature of the doped samples via various equipments such as X-ray diffractometer(XRD),Raman spectrometer and physical property measurement system(PPMS).In addition,we have applied a first-principles calculation method based on density generalized theory to investigate the crystal structure and electronic structure of the material.The main research work of this paper includes:1.We have carried out experiments on potassium-and rubidium-doped2-phenylnaphthalene using a two-step preparation process with constant-temperature heating sonication and low-temperature high vacuum annealing.The XRD measurements show that the potassium-doped samples mainly contained pure 2-phenylnaphthalene and amorphous phases,while the XRD patterns of the rubidium-doped samples are significantly different from the one of pure 2-phenylnaphthalene,which indicate that we obtain well-crystalline rubidium-doped 2-phenylnaphthalene samples.The magnetic property measurements show that pure 2-phenylnaphthalene exhibits diamagnetic property,while the rubidium-doped samples exhibit paramagnetic behavior throughout the test temperature range(1.8-300 K)and have a magnetic moment of 0.55μ_Bon each molecule.In addition,there exist multiple redshifts of Raman modes in the Raman spectra,which originate from the softening effect of the Raman modes caused by the 5s electron transfer of rubidium to the 2p orbital of carbon.This charge transfer simultaneously forms a local magnetic moment on the molecule.2.We have carried out experiments on potassium-and rubidium-doped2-phenylquinoline using a two-step preparation process with constant-temperature heating sonication and low-temperature high vacuum annealing.XRD measurements show that we obtain only well-crystallized potassium-doped 2-phenylquinoline samples.The magnetic measurements show that pure 2-phenylquinoline exhibits diamagnetism,while the potassium-doped samples exhibit weak ferromagnetism with a Curie temperature of about50.0 K.The potassium-doped 2-phenylquinoline molecular crystal has a P1 spatial symmetry group and the molar ratio of potassium to 2-phenylquinoline is 1:1,as shown by X-ray diffraction tests and first-nature principle calculations.Calculations of the electronic structure show that the magnetic moments are formed by the transfer of 4s electrons from K to the 2p orbitals of carbon,which is further confirmed by the redshift phenomenon of Raman spectroscopy,the distribution of spins on both quinoline molecules and phenyl functional groups,the antiferromagnetic alignment of adjacent molecular magnetic moments in the ab plane with non-co-linear alignment,and the ferromagnetic alignment between adjacent molecular magnetic moments along the c-axis direction with each cell having 0.004μ_Bnet magnetic moment,which is the reason for the weak ferromagnetism.3.We have carried out experiments on potassium-and rubidium-doped1-phenylisoquinoline using a two-step preparation process with constant-temperature heating sonication and low-temperature high vacuum annealing.The XRD measurements show that the potassium-doped samples form mainly amorphous phases,while the XRD patterns of rubidium-doped 1-phenylisoquinoline samples are significantly different from the one of pure1-phenylisoquinoline,indicating that we obtain rubidium-doped 1-phenylisoquinoline samples with good crystallinity.Magnetic measurements show that pure 1-phenylisoquinoline exhibits anti-magnetic properties,while rubidium-doped 1-phenylisoquinoline samples exhibit low-dimensional antiferromagnetic characteristics below 225 K.In addition,we observe multiple Raman mode redshifts in the Raman spectra,which arise from the softening effect of the Raman modes caused by the 5s electron transfer of rubidium to the 2p orbital of carbon,and the charge transfer leads to the formation of localized magnetic moment on the molecule.The research works in this thesis extend the study of alkali metal-doped aromatic hydrocarbons to mixed aromatic hydrocarbons with both fused and non-fused rings,which not only provides a new way to explore organic magnets,but also helps to understand the intra-and inter-molecular magnetic interactions of mixed aromatic hydrocarbons.