Specific Heat Anomaly for H ≥ 28.5 T in CeIrIn5

Recently Takeuchi reported a weak, 'metamagnetic-like' increase in the magnetization around 42 T in single crystals of CeIrIn₅ for field in the c-direction. We report specific heat measurements on single crystal CeIrIn₅, H parallel c-axis, measured in the dc hybrid magnet at NHMFL in Tallahassee between 1.4 and 10 K. A clear anomaly in C/T in 35 T is observed to peak at 1.8 K, with an entropy of 6% of Rln2. This anomaly grows in size and shifts upwards in temperature (both monotonically) with increasing H until at 45 T T_peak=4.1 K, with the entropy associated with the transition equal to 14 % of Rln2. C/T data at 32 T show³ only the high temperature side of the peak occurring above 1.4 K, while C/T data at 28.5 T show no anomaly down to 1.4 K. This is consistent with our T_peak vs H data, which imply T_peak→0 at 26 T.