Nowadays,the contradiction of the global energy issue is becoming increasingly prominent.The development of new energy materials is taken as a breakthrough for solving the energy crisis.The rare earth permanent magnets,as a kind of new energy materials,play an important role in new energy vehicles,wind power generation and aerospace.SmCo5 is a good candidate for high-temperature permanent magnet materials due to its excellent intrinsic magnetism and high Curie temperature.With the increasing requirement for permanent magnet materials in high-technology fields,the improvement of the magnetic properties and reduction of costs are necessary for SmCo5.The equiatomic multicomponent alloys,i.e.high entropy alloys(HEAs),break the limitation of the composition design of traditional alloys.HEAs show excellent properties and long-term development prospects.The concept of multicomponent design is first introduced into SmCo5 intermetallic compounds,combining the"disorder" of HEAs with the "order" of intermetallic compounds,and exploring new 1:5 type rare earth-transition metal high entropy intermetallic compounds(HEICs).The rare earth-transition metal HEICs with 1:5 type were prepared by vacuum arc melting technology.The studies cover their crystal structures,compositions,magnetization and magnetic transition temperatures,and Vickers hardness.The thermodynamic parameters of these HEICs were calculated.The single-phase HEAs and(Sm,R1,...,Rn)Co5 HEICs were theoretically studied by using solid and molecular empirical electron theory(EET)for revealing the relationships between valence electron structures(VESs)and physical properties.This work has achieved the following innovative results:1.The concept of high entropy has been first introduced into SmCo5 intermetallic compounds.Three series of HEICs(Sm,R1,...,Rn)Co5,Sm(Co,T1,...,Tm)5 and(Sm,R1,...,Rn)(Co,T1,...,Tm)5(R=La,Ce,Pr,Nd and Y;T=Ni and Cu)have been designed and prepared successfully.The high entropy design is realized for the first time at Sm or Co site and both Sm and Co sites in SmCo5 type intermetallic compounds.The kinds of high entropy materials and the ideas for the design of new intermetallic compounds are expanded.2.The crystal structure shows that the 1:5 type rare earth-transition metal HEICs have a CaCu5-type hexagonal structure with a space group of P6/mmm.The crystal positions are occupied by rare-earth atoms at 1a(0.0,0)site,transition metal atoms at 2c(1/3.2/3.0)and 3g(1/2,0,1/2)sites,respectively.The composition analysis shows that the atomic percentages of elements at the Sm site or Co site are close to the equiatomic ratio.The single-phase 1:5 rare earth-transition metal HEICs are confirmed by the analysis of phase and composition.The mixing enthalpy and the mixing entropy of these HEICs are-14.72~-10.56 kJ/mol and 1.10R~6.88R,respectively.3.The magnetic moments at room temperature of(Sm,R1,...,Rn)Co5 are related to the rare earth atoms at Sm site.Pr and Nd with large 4f magnetic moments can increase the magnetic moments of(Sm,R1,...,Rn)Co5,while La and Y lead to the decrease of the magnetic moments.(Sm,R1,...,Rn)Co5 shows strong uniaxial anisotropy at room temperature,and the magnetocrystalline anisotropy fields are in the range of 97~140 kOe.(Sm1/3Cei/3Pr1/3)Co5 has the potential application of a highperformance permanent magnet due to its large magnetocrystalline anisotropy field(138 kOe),coercivity(6.9 kOe),and maximum magnetic energy product(1 8.0 MGOe).The anisotropic field and Vickers hardness of(Sm,R1,...,Rn)Co5 are enhanced by adding Y.4.Sm(Co1/3Ni1/3Cu1/3)5 orders ferromagnetically and its Curie temperature is 417 K.At room temperature,the easy magnetization direction of Sm(Co,T1,...,Tn)5 is along the c-axis.Sm(Co,T1,...,Tn)5 have strong uniaxial anisotropy,and their magnetocrystalline anisotropy fields range from 186 kOe to 207 kOe.It is found that Cu is beneficial to enhance magnetic anisotropy and coercivity.The "dilution" effect of Ni and Cu reduces the room-temperature magnetic moments of Sm(Co,T1,...,Tn)5.5.(Sm,R1,...,Rn)(Co1/3Ni1/3Cu1/3)5 with Nd show the spin glass state and fieldinduced ferromagnetic transition;Nd-free(Sm,R1,...,Rn)(Co1/3Ni1/3Cu1/3)5 only show the field-induced ferromagnetic transition.The spin glass "freezing" temperatures Tf are ranging from 36 K to 66 K and the Curie temperatures Tc are ranging from 204 K to 348 K.The spin-glass state mainly comes from the disordered spin interaction of rare earth atoms at the Sm site.The substitution of Nd for Sm atom causes the reduction of magnetic anisotropy,the increase of disorder of rare earth atoms,and the spin-glass state of(Sm,R1,...,Rn)(Co1/3Ni1/3Cu1/3)5 at low temperatures.Between 204 and 348 K,the spin alignments are driven by the external magnetic field along the magnetic field direction and the "melting" of the antiferromagnetic state cause the field-induced ferromagnetic transition.6.The correlations between the VESs and the thermal,mechanical,and magnetic properties of face centered-cubic(FCC)and body centered-cubic(BCC)HEAs,and(Sm,R1,...,Rn)Co5 HEICs have been studied by using the EET for the first time.The theoretical bond lengths and magnetic moments agree with the experimental ones well.The covalence electron pair numbers on the strongest bond can modulate the melting point and hardness.The melting point and hardness increase with the increase of the covalence electron pair numbers on the strongest bond.The cohesive energy increases with the increase of covalent electron number.The large covalent electron number indicates that the binding ability between atoms is enhanced and the crystal structure is more stable.The magnetic moments of the(Sm,R1,…,Rn)Co5 mainly originate from the 3d magnetic electrons of Co.The magnetic moments of(Sm,R1,...,Rn)Co5 are influenced by rare earth due to their exchanging interaction with the magnetic electron numbers of Co atom.The magnetic moments of Co at the 2c site are larger than those of Co at the 3g site.It shows that the contribution of Co at 2c site to the magnetic moments is larger than those of Co at the 3g site.The Curie temperature of(Sm,R1,…,Rn)Co5 increases with the increase of the magnetic electron numbers. |