EMPTY 4F(1)-STATE MAGNETOOPTICAL SPECTROSCOPY IN LASE

We report the first observation of the magneto-optical signal of an em pty spin-polarized 4f State in a paramagnetic metal. At 1.5 K and in a magnetic field of 10 T the Ken rotation spectrum of LaSe shows a rema rkably sharp positive peak of 2.1 degrees at 2.77 eV and a broader and smaller structure at 3.01 eV. A comparison with CeSe, which displays a similar sharp peak with opposite sign but no second peak, gives evid ence that the LaSe signal is due to 5d --> 4f (J = 5/2) and 5d --> 4f (J = 7/2) transitions, while the magneto-optical signal in CeSe corres ponds to a 4f (J = 5/2) --> 5d transition.