Physical Properties Of Heavy Fermion Materials LnFe₂Ga₈（Ln=Nd,Pr,and Sm）

The study of heavy fermion materials has always been one of the important fields in strong correlation system.The heavy fermion properties of Ln M₂X₈（Ln=La,Ce,Pr,Nd,Sm etc.;M=Fe,Co,Ru etc.;X=Al,Ga,and In）family materials have attracted the attention of researchers in related fields.They crystallize in Ca Co₂Al₈-type orthorhombic structure with space group Pbam（No.55）,where Ln atoms form quasi-one-dimensional chain along the c-axis.Thus,the magnetism of 4f electrons is expected to show one-dimensional-like characteristics.Only a few members of the series have been explored so far,and previous studies of some systems in this series have revealed important correlated electron behaviors,such as magnetic ordering,heavy fermion state,crystalline electric field effect,Kondo lattice,and quantum critical point etc.These correlated electron behaviors are the key of strongly correlated electron systems.Therefore,it is very important for understanding the electron behaviors of this series of materials to explore single crystal materials of Ln M₂X₈ series and study their physical properties.Firstly,single crystals of NdFe₂Ga₈ were successfully synthesized by using Ga-flux,and the results of single crystal characterization and powder XRD confirm that NdFe₂Ga₈ crystallize in orthorhombic system with space group of Pbam,where Nd atoms show quasi-one-dimensional chain arrangement along the c-axis.The results of magnetism,specific heat,and electrical resistivity in different directions reveal that NdFe₂Ga₈ has strong magnetic anisotropy.For H//c and H=70 k Oe,the suppression of the magnetic order results in quantum critical behaviors of conventional three-dimensional spin-density-wave type.However,For H>30 k Oe,the temperature dependence of the electrical resistivity is replaced by a T^0.5 behavior at very low temperature,which is attributed to the magnetic-filed-induced ferromagnetic moment.The results of physical property measurement indicate that there may be couplings between the antiferromagnetic quantum critical fluctuations and ferromagnetic fluctuations induced by the magnetic field.Secondly,single crystals of PrFe₂Ga₈ were successfully synthesized by replacing Nd atoms with Pr atoms.The results of single crystal characterization and powder XRD confirm that PrFe₂Ga₈ also belongs to orthorhombic system with space group of Pbam.The low-temperature measurements of the magnetic susceptibility,specific heat,and electrical resistivity reveal that PrFe₂Ga₈ exhibits an antiferromagnetic order at about14 K,and the antiferromagnetic order results in abnormal behavior of electrical resistivity.The magnetic anisotropy of PrFe₂Ga₈ is revealed by the measurement of H//c and H⊥c.The specific heat data show that the electronic specific heat coefficientγis about 131.42 m J/mol-K²,suggesting this material is a heavy-fermion material.Finally,single crystals of SmFe₂Ga₈ were successfully synthesized by replacing Pr atom with Sm atom.The results of single crystal characterization and powder XRD confirm that SmFe₂Ga₈ also belongs to orthorhombic system with space group of Pbam.The low-temperature behaviors of magnetic susceptibility,specific heat,and electrical resistivity have revealed an obvious magnetic transition at 10.5 K which is robust to the magnetic field.The specific heat data show that the electronic specific heat coefficientγis about 272.19 m J/mol-K²,suggesting this material is a heavy-fermion material.