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The temperature dependencies of the electrical resistivity ρ for current along and perpendicular to the c axis were measured on single crystalline UNiAl under various hydrostatic pressures. The ρ(T) curves at ambient pressure exhibit a Cr anomaly around the Nee´l temperature T[sub N]. Application of pressure causes a reduction of T[sub N] value. Linear extrapolation of low-pressure T[sub N] vs p data yields an estimate of a critical pressure for antiferromagnetism p[sub c]approx. 10 GPa. Measurements above 1 GPa, however, reveal a collapse of the antiferromagnetic (AF) ordering already below 3 GPa, although AF correlations seem to affect resistivity behavior ρ(T) in pressures up to 8 GPa. A sudden change of the ρ(T) curve character for i⊥c and T

We report on magnetic-history dependent magnetoresistance in UNiAl at various temperatures. The magnetic-field (applied along the c-axis) induced irreversibility of magnetoresistance is strongest at the lowest temperature of measurement (0.5 K) and decays with increasing temperature to vanish around T*=7 K. Below this characteristic temperature T* the metamagnetic transition in UNiAl is of the first-order type. When increasing temperature above T*, the transition becomes gradually smeared out. In addition, we have observed that the irreversibility of magnetoresistance emerges at low temperatures already after exposing UNiAl to magnetic fields ⩾9 T, i.e. crossing the metamagnetic transition at 11.35 T is not the necessary condition to induce the irreversibility. Based on these magnetoresistance data, a modified magnetic phase diagram is proposed. [Copyright &y& Elsevier]

Results of low-temperature specific-heat (Cp) measurements of UNiAl single crystal in magnetic fields B&les;14 T are presented. At temperatures <7 K, this antiferromagnet exhibits a first-order metamagnetic transition at the critical field Bc&ap;11.4 T (when applied parallel to the c-axis). In the same temperature range, different Cp vs. T curves are obtained in zero magnetic field depending on the magnetic history of the sample (zero-field-cooled (ZFC)=cooling to T<7 K in zero field, field cooled (FC)=cooling in a field of 14 T parallel to c). The magnetic-field-induced irreversibility is clearly evidenced on the Cp/T vs. B data obtained at 3.2 K. For a measurement cycle; 0 (starting from ZFC state)→14→0 T the “increasing field” Cp, ZFC/T and “decreasing field” Cp, FC/T data clearly differ in fields <9 T and (Cp, ZFC/T)0 T>(Cp, FC/T)0 T. However in both cases, we have observed (for B<9 T) a Cp/T∼κcB2 dependence with different κc values. The results are discussed in the context of earlier-reported magnetic-history effects in magnetic and other electronic properties. [Copyright &y& Elsevier]

UNi2/3Rh1/3Al, a solid solution of UNiAl (Antiferromagnet (AF) with TN−19.3 K) and URhAl (Ferromagnet (F) with TC−27 K) exhibits no magnetic order due to a delicate balance of AF and F interactions. We report on a single-crystal susceptibility χ, magnetization M and resistivity ρ study. The huge uniaxial magnetic anisotropy typical for the parent compounds is preserved in UNi2/3Rh1/3Al. The χc vs. T (ρ vs. T) data exhibit a maximum (minimum) at 10 K. The Mc(B) curve at 1.6 K has a pronounced S-shape with an inflection around 12 T. The increase of ρ with decreasing T below 10 K is removed by magnetic fields. The low-T anomalies are attributed to proximity of magnetic order and AF correlations. The NFL features indicated earlier on polycrystals are not fully confirmed by single-crystal data. [Copyright &y& Elsevier]