Specific heat near Hmetamag=18 T in UPd2Al3

We have measured the specific heat vs. temperature in fields to 20 T of UPd2Al3 in order to try to determine the reason for the disagreement in the magnetic phase diagram as determined by magnetization and X-ac vs. resistivity measurements, with the resistivity measurements showing the magnetic anomaly trending towards T = 0 as H --> H-metamag. Our data show a slight monotonic suppression of TN with increasing field in agreement with both previous magnetoresistance and magnetization data until H --> H-metamag. However, as field exceeds 17 T the specific heat shows a peak (presumably in a narrow field range connected with both antiferromagnetism and the H > H-metamag magnetization anomaly) that is suppressed with further increases infield no lower in temperature than 11.7 K (in contrast to the feature in the magnetoresistivity which, e.g., occurs at 8.4 K in 18 T) before it starts to move up in temperature with increasing field at H greater than or equal to 18 T (H-metamag). Possible causes of the specific heat anomaly for H > H-metamag, as well as for the discrepancy, between the specific heat and the resistivity as H --> H-metamag, are discussed.