Detection of electron spin resonance via magnetoimpedance in La_1−xCa_xMnO₃

We demonstrate a method to detect the spin resonance of Mn electrons at room temperature in paramagnetic samples of La_1−xCa_xMnO₃ with x = 0.35, 0.40, and 0.45 using a simple magnetoimpedance (MI) measurement. The magnetic field dependent “ac” resistance and reactance were simultaneously measured at 300 K using a single-port impedance analyzer by passing a current of frequency f = 500 MHz–3 GHz directly through the sample. The magnetoresistance of each sample increased abruptly at a critical value of the applied magnetic field while the magnetoreactance displayed a dip. Both these features shifted linearly toward higher “dc” magnetic fields with increasing frequency of the current. We suggest that these anomalies in MI are imprints of spin resonance from the Mn electrons. Our results were also verified using a conventional broadband spectrometer (f = 2–10 GHz). Thus, the electrical detection of paramagnetic resonance using a low-cost impedance analyzer, as demonstrated here, can provide an alternate method to investigate magnetic resonances in various materials.