High-temperature ferromagnetism in Cr_1+xPt_5-xP

We present the growth and basic magnetic and transport properties of Cr1+xPt5-xP. We show that single crystals can readily be grown from a high-temperature solution created by adding dilute quantities of Cr to Pt-P based melts. Like other 1-5-1 compounds, Cr1+xPt5-xP adopts a tetragonal P4/mmm structure composed face-sharing CrPt3 like slabs that are broken up along the c axis by sheets of P atoms. EDS and x-ray diffraction measurements both suggest Cr1+xPt5-xP has mixed occupancy between Cr and Pt atoms, similar to what is found in the closely related compound CrPt3, giving real compositions of Cr1.5Pt4.5P (x = 0.5). We report that Cr1.5Pt4.5P orders ferromagnetically at T-C = 464.5 K with a saturated moment of approximate to 2.1 mu(B)/Cr at 1.8 K. Likely owing to the strong spin-orbit coupling associated with the large quantity of high Z, Pt atoms, Cr1.5Pt4.5P has exceptionally strong planar anisotropy with estimated anisotropy fields of 345 kOe and 220 kOe at 1.8 K and 300 K, respectively. The resistance of Cr1.5Pt4.5P has a metallic temperature dependence with relatively weak magnetoresistance. Electronic band structure calculations show that CrPt5P has a large peak in the density of states near the Fermi level, which is split into spin majority and minority bands in the ferromagnetic state. Furthermore, the calculations suggest substantial hybridization between Cr-3d and Pt-5d states near the Fermi level, in agreement with the experimentally measured anisotropy.