Doping of Ga in antiferromagnetic semiconductor α-Cr2O3 and its effects on magnetic and electronic properties

Abstract

The samples of Ga doped Cr 2 O 3 oxide have been prepared using chemical co-precipitation route.X-ray diffraction pattern and Raman spectra have confirmed rhombohedral crystal structure with space group R3 C. Magnetic measurement has indicated the dilution of antiferromagnetic (AFM) spin order in Ga doped α-Cr 2 O 3 system oxide, where the AFM transition temperature of bulk α-Cr 2 O 3 oxide at about 320 K has been suppressed and ferrimagnetic behavior is observed from the analysis of the temperature dependence of magnetization data below 350 K. Apart from Ga doping effect, the spin freezing (50 K-70 K) and superparamagnetic behavior of the surface spins at lower temperatures, typically below 50 K, have been exhibited due to nano-sized grains of the samples. All the samples showed non-linear current-voltage (I-V) characteristics. However, I-V characteristics of the Ga doped samples are remarkably different from α-Cr 2 O 3 sample. The I-V curves of Ga doped samples have exhibited many unique electronic properties, e.g., bi-stable (low resistance-LR and high resistance-HR) electronic states and negative differential resistance (NDR). Optical absorption spectra revealed three electronic transitions in the samples associated with band gap energy at about 2.67-2.81 eV, 1.91-2.11 eV, 1.28-1.35 eV, respectively. 2 Key Words: Magnetic semiconductor; tuning of band gap; negative differential resistance; I-V loop, bi-stable electronic state.

Non-equilibrium character of resistive switching and negative differential resistance in Ga-doped Cr2O3 system

“…The polycrystalline samples of Cr 2-x Ga x O 3 (x = 0.55, 0.83) system (CrGaO) were prepared by chemical reaction and subsequent thermal annealing at 800 0 C. The highly Ga doped sample (Cr 1.17 Ga 0.83 O 3 ) has shown higher current in comparison to low Ga content sample (Cr 1.45 Ga 0.55 O 3 ). It is worthy to mention that I-V loop in the α-Cr 2 O 3 sample is negligibly small in comparison to Ga doped α-Cr 2 O 3 sample, as reported within voltage limit ± 30 V [23] and also true for voltage limit ± 200 V (not shown in figure). The results of the I-V curve analysis also suggest the presence of a significant amount of microscopic level defects (oxygen vacancies-positive charge and oxygen ionsnegative charge), which played a crucial role in the observed bipolar resistive switching process.…”

“…Details of the preparation of Ga doped Cr 2 O 3 samples by chemical co-precipitation and structural phase stabilization have been described in earlier work [23]. In the present work, we used the samples with chemical compositions Cr 1.45 Ga 0.55 O 3 and Cr 1.17 Ga 0.83 O 3 .…”

“…We present resistance switching and NDR phenomena at room temperature in a new material, developed by incorporating non-magnetic Ga atoms in the antiferromagnetic α-Cr 2 O 3 . The magnetic measurement [23] has shown Ga doped α-Cr 2 O 3 system as a diluted antiferromagnet with ordering temperature at about 50 K and a typical paramagnet at room temperature. This work is devoted to study the non-equilibrium I-V properties in thin pellet shaped samples of polycrystalline Ga doped α-Cr 2 O 3 system using Pt/CrGaO/Pt structure.…”

Tuning of structural phase, magnetic spin order and electrical conductivity in mechanical alloyed material of α-Fe2O3 and α-Cr2O3 oxides

“…On the other hand, a kink (magnetic field independent) appeared at ~ 51 K and 55 K for FeCr2MA10 and FeCr5MA10 samples, respectively. Such low temperature magnetic anomaly is attributed to freezing of a fraction of surface spins in AFM nanoparticles [9,22]. The normalized MZFC(T) curves for FeCr2MA10 sample showed a minor increment by increasing the field up to 2 kOe.…”

“…An additional peak at 665-670 cm -1 in the spectra of Fe 1-x Cr x O 3 samples with respect to the spectrum of α-Fe 2 O 3 [20] and α-Cr 2 O 3 [22] suggest a modified spin-lattice structure. The band (peak) position (within simple harmonic approximation) obeys the equation v = .…”