Magnetic and thermal properties of CeIrIn5 and CeRhIn5

We studied the magnetic properties in a non-magnetic heavy-fermion compound CeIrIn5 and an antiferromagnetic compound CeRhIn5 with the tetragonal structure. High-field magnetization of CeIrIn5 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 CeRhIn5. The magnetization is of the x-y type. The former transition indicates a 1/ cos theta dependence, where the theta 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 CeRhIn5. 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.