Susceptibility, magnetization, and specific heat in the paramagnetic and ferromagnetic regions of (Y1−xUx)B4

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Abstract
An anomalous magnetic phase diagram for (Y1−xUx)B4 has previously been reported. This system is paramagnetic for x>0.6, ferromagnetic for 0.1<xxf electrons upon alloying UB4 with nonmagnetic YB4 due to a reduction of f‐f overlap. The temperature and x dependence of the magnetic susceptibility is consistent with a two site model. This model assumes that the 5f electrons associated with U ions that have four or less nearest neighbors become localized and develop a stable paramagnetic moment. From our analysis, we obtain a paramagnetic moment of (2.6±0.2) μB. The saturation moment per U ion for (Y0.7U0.3)B4 is (0.32±0.03) μB. The specific heat of (Y,U)B4 shows a substantial enhancement as x decreases but the origin of this enhancement is not understood at this time. These results are presented and discussed in relation to the expected behavior as the system approaches the ferromagnetic instability.