Broadband magnetotransport in La0.6Sr0.4Mn1−xGaxO3 (0.0 ≤ x ≤ 0.3) at room temperature

We report the magnetic field (−2.5 kOe ≤ Hdc ≤ 2.5 kOe) dependence of ac magnetoresistance (ac MR) and magnetoreactance (MX) in bulk samples of La0.6Sr0.4Mn1−xGaxO3 (0 ≤ x ≤ 0.3) carrying radio frequency current (f = 10 MHz–3 GHz) at 300 K. Samples with x ≤ 0.10 are ferromagnetic (FM) and those with x ≥ 0.2 are paramagnetic (PM) at 300 K. While the ac MR in FM samples is negative and shows a single sharp peak at Hdc = 0 at low frequencies, positive double peaks emerge at Hdc = ±Hp for f > 500 MHz, and they shift toward higher Hdc with increasing f. The positive ac MR is larger (∼75% at Hdc = Hp = 800 Oe at 3000 MHz) than 20% negative ac MR for Hdc = 2.5 kOe at 10 MHz. The PM samples also show negative ac MR and single peak for 100 MHz