The DC transport properties of and the radio-frequency (RF) wave absorption (at 1.33 MHz) in a ceramic sample of La0.5Sr0.5CoO 3−δ are measured. The Curie temperature, Tc, of the sample is about 250 K. A giant negative magnetoabsorption effect is found. In the vicinity of Tc, the absolute value of the magnetoabsorption is about 38% in the rather low magnetic field 2.1 kOe. This differs drastically from the measured DC magnetoresistance (MR) δ(H) = [R(0) − R(H)]/R(0) which is a mere 0.26 % near Tc in the same field and increases to about 2.15 % in H = 20 kOe. The phenomenon can be understood taking into account that the magnetoabsorption is determined by influence of magnetic field on the conductivity and the magnetic permeability, while the MR is determined solely by the former. The magnetoabsorption effect can be used to develop RF devices controlled by magnetic field and temperature.

The DC transport properties of and the radio-frequency (RF) wave absorption (at 2:525 MHz) in a sample of La 0:67 Sr 0:33 MnO 3 prepared by floating-zone method are measured. The Curie temperature, T c ; of the sample is about 374 K: Giant temperature and magnetic-field variations in RF absorption are found in the vicinity of T c : Relative change of the RF absorption in magnetic field (magnetoabsorption) is about 67% in field 2:1 kOe and about 55% in field 1 kOe: This giant magnetoabsorption effect can be used to develop RF devices controlled by temperature and low magnetic field. A weak temperature dependence of magnetoabsorption for the sample studied in the range from room temperature to about 350 K makes it especially attractive for practical use. The RF study supplemented with transport, magnetoresistive and magnetic measurements enables us to discuss the optimal properties of manganite samples for observation of giant magnetoabsorption in low field. r

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