Detection of electron paramagnetic resonance in La0.6Ca0.4MnO3 using a copper stripcoil

Abstract

Recently, we had reported the detection of electron paramagnetic resonance (EPR) from magnetoimpedance (MI) measurements in bulk La0.60Ca0.40MnO3 (LCMO) samples using radio frequency (rf) currents [U. Chaudhuri and R. Mahendiran, Appl. Phys. Lett. 115, 092405 (2019)]. Here, we report an alternative method which involves measuring the effective MI changes of a copper stripcoil that encloses the LCMO sample. Magnetoresistance (∆R/R0) and magnetoreactance (∆X/X0) of the sample were measured indirectly via the stripcoil for frequencies of current from f = 0.5 to 2.5 GHz. During the field sweep, ∆R/R0 shows an abrupt increase that is accompanied by a dip in ΔX/X0 at a critical value of dc magnetic field (Hc) when f ≥ 0.9 GHz. Hc increased linearly with frequency (f) of the current in the stripcoil, satisfying the EPR relation fr = (γ/2π)Hdc, where γ is the gyromagnetic ratio and fr is the resonance frequency. The same stripcoil and the sample were also used to measure microwave power absorption using a vector network analyzer. The features observed in both these techniques were strikingly similar to the results obtained from the direct MI measurement in LCMO, which confirms the electrical detection of EPR.