Exploration Of New Magnetic Quantum Critical Materials

Emergent quantum phase transitions have attracted extensive interest in condensed matter physics.Upon applying a nonthermal control parameter such as pressure,chemical doping or magnetic fields,the ground state in heavy fermion compounds can be effectively tuned,with the emergence of exotic quantum phenomena such as quantum criticality,unconventional superconductivity and non-Fermi liquid behavior.In the field of quantum phase transitions,there is still lack of experimental evidence for FM-QCP,and it exist a lot of issues to figured out in the field of anti ferromagnetic quantum criticality.It is urgent to look for universality observed in quantum criticality,thus it is the priority to explore a new quantum magnetic quantum critical material in the field of antiferromagnetic quantum criticality.This thesis is devoted to studying the ferromagnetic(FM)compound CeRh6Ge4,and the antiferromagnetic compounds Ce2IrGa12 and Sm4Co3Ga16.The experimental results divided into five chapters,as follows:(1)The growth,magnetic properties and pressure-induced ferromagnetic quantum critical point(QCP)in single crystal of CeRh6Ge4.High-quality single crystals of CeRh6Ge4 were grown using a flux method.CeRh6Ge4,which has a quasi-1D structure,is a new heavy fermion ferromagnet at ambient pressure,which has a ferromagnetic transition at Tc=2.5K.A pressure induced FM-QCP reached at Pc?0.8GPa,and strange metal behavior emerges in the vicinity of the FM-QCP,with??T and C/T ? log(T*/T).These features provide strong evidence in favor of a local QCP in CeRh6Ge4,instead of an itinerant scenario.(2)FM-QCP in CeRh6Ge4 induced by silicon-doping.A FM-QCP is achieved at a silicon concentration of xcSi?0.135,and non-Fermi liquid behavior together with strong quantum fluctuations also develop in the vicinity of QCP with C/T ?log(T*/T)and a Gruneisen ratio ?(T)? T-050.The disorder effect originating from silicon-doping affects the resistivity in the vicinity of the QCP.The critical exponent ?=0.5(?(T)? T-?)observed at the silicon-doped FM-QCP indicates that it may be an unconventional local QCP.(3)FM-QCP in CeRh6Ge4 induced by cobalt doping.A FM-QCP is achieved at a cobalt concentration of xcCo?0.05,and non-Fermi liquid behavior and together with strong quantum fluctuations are observed in the vicinity of the QCP with C/T ?log(T*/T),?(T)? T1.5 and a Gruneisen ratio ?(T)? T-0.72.In cobalt-doped CeRh6Ge4,the critical exponent ?-0.72 is close to the value of ?-0.7 observed in YbRh2Si2,indicating that FM-QCP may also be an unconventional local QCP.(4)Structural and magnetic properties of antiferromagnetic Ce2IrGa12.Ce2IrGa12 crystallizes in a tetragonal structure with the space group P4/nbm,and undergoes an antiferromagnetic transition below TN=3.1K.Ce2IrGa12 exhibits strongly anisotropic magnetic properties for H?ab and H?c.The antiferromagnetism in Ce2IrGa12 is gradually suppressed by field and evolves to a polarized state,indicating a lack of field-induced quantum criticality.A metamagnetic transition is found for fields applied within the ab plane,where the presence of a field-induced magnetic phase is found.TN shows an enhancement upon applying pressures,indicating that Ce2IrGa12 is situated on the left side of the Doniach phase diagram,with well localized 4f electrons.(5)Single crystal growth and anisotropic physical properties of Sm4Co3Ga16.We synthesized single crystals of Sm4Co3Ga16 using a flux method.No superconducting transition is detected in the single crystals,but it undergoes an antiferromagnetic transition at 6.7K.In addition,the Sm3+ state in Sm4Co3Ga16 is well localized.