Structural and Physical Properties Diversity of New CaCu5-Type Related Europium Platinum Borides
Three novel europium platinum borides have been synthesized by arc melting of constituent elements and subsequent annealing. They were characterized by X-ray powder and single-crystal diffraction: EuPt4B, CeCo4B type, P6/mmm, a = 0.56167(2) nm, c = 0.74399(3) nm; Eu3Pt7B2, Ca3Al7Cu2 type as an ordered variant of PuNi3, R3̅m, a = 0.55477(2) nm, c = 2.2896(1) nm; and Eu5Pt18B6–x, a new unique structure type, Fmmm, a = 0.55813(3) nm, b = 0.95476(5) nm, c = 3.51578(2) nm. These compounds belong to the CaCu5 family of structures, revealing a stacking sequence of CaCu5-type slabs with different structural units: CaCu5 and CeCo3B2 type in EuPt4B; CeCo3B2 and Laves MgCu2 type in Eu3Pt7B2; and CaCu5-, CeCo3B2-, and site-exchange ThCr2Si2-type slabs in Eu5Pt18B6–x. The striking motif in the Eu5Pt18B6–x structure is the boron-centered Pt tetrahedron [BPt4], which build chains running along the a axis and plays a decisive role in the structure arrangement by linking the terminal fragments of repeating blocks of fused Eu polyhedra. Physical properties of two compounds, EuPt4B and Eu3Pt7B2, were studied. Both compounds were found to order magnetically at 36 and 57 K, respectively. For EuPt4B a mixed-valence state of the Eu atom was confirmed via magnetic and specific heat measurements. Moreover, the Sommerfeld value of the specific heat of Eu3Pt7B2 was found to be extraordinarily large, on the order of 0.2 J/mol K2.
Spin fluctuations in Gd3Rh induced by f–d exchange: the influence on the T-linear specific heat
The results of specific heat, magnetization and magnetic susceptibility measurements for the antiferromagnetic (AF) compound Gd3Rh are presented. Below its N?el temperature TN = 112 K, this compound exhibits a field-induced phase transition from the AF to the ferromagnetic state in a relatively small magnetic field (~0.4 T). Specific heat measurements revealed a giant enhancement of the coefficient of the T-linear specific heat in Gd3Rh (? = 118 mJ mol?1 K?2) in comparison with that observed for the isostructural nonmagnetic partner Y3Rh (? = 11 mJ mol?1 K?2). An anomalous behaviour of the heat capacity as well as a set of peculiarities of magnetic properties in Gd3Rh are associated with the existence of spin fluctuations induced by f?d exchange interaction in the d-electron subsystem that arises from features of the crystal and electronic structure of the R3M-type compounds.
Low temperature properties ofY3Ni
The electrical resistivity (ρ) in the temperature range from 20mK up to 1000K and the low temperature specific heat ofY3Ni have been studied. Neithera magnetic order nor a superconducting transition have been found. An enhanced spin fluctuation contributution to the temperature dependence of the resistivity is concluded from the low temperatureT2 behaviour and the pronounced negative curvature at elevated temperatures in ρ vs. T. However, the large A/γ2Y3Ni (5.6×10−5 is beyond the spin fluctuation regime in the Kadowaki—Woods plot) does not enable us to classify this compound as a typical spin fluctuation system.