Magnetic and Thermal Properties of CeIrIn5and CeRhIn5

We studied the magnetic properties in a non-magnetic heavy-fermion compound CeIrIn 5 and an antiferromagnetic compound CeRhIn 5 with the tetragonal structure. High-field magnetization of CeIrIn 5 shows a weak metamagnetic transition around 420 kOe for the field along the [001] direction, while the magnetization gradually increases up to 500 kOe for [110]. On the other hand, we observed a two-step metamagnetic transition for the field perpendicular to [001] at 20 and 500 kOe in CeRhIn 5 . The magnetization is of the x - y type. The former transition indicates a 1/cos θ dependence, where the θ means a tilted angle of the field direction from the (001) plane. From the magnetic susceptibility and high-field magnetization measurements, we formed a magnetic phase diagram in CeRhIn 5 . The temperature dependences of the magnetic susceptibility and thermal expansion coefficient of both compounds were analyzed on the basis of the crystalline electric field model.