Magnetic field induced metastability in the self-doped manganites

We observe an interesting scenario of field induced metastabilities in the resistivity measurements. The resistivity exhibits a bifurcation of zero-field cooled and field-cooled (FC) temperature dependence below the paramagnetic to ferromagnetic transition (Tc). The clear evidence of inverse thermal hysteresis of resistivity is observed under FC condition in between 85 and 200 K, indicating the first order phase transition at Tc. The additional observation of minor hysteresis loops confirms the phase coexistence. The interesting features in the dynamics of resistivity is observed at 40 K, which is suggested due to the effect of domain wall dynamics. PACS numbers: 75.47.Lx, 72.20.-i, 75.50.Lk Magnetic field induced metastability in the self-doped manganites 2 The mixed valent manganites with perovskite structure are fascinating due to the wealth of physical properties arising from interplay between structural, electronicn, and magnetic properties of the system [1, 2]. The co-existence of different competing factors often gives rise to metastable behaviour, which are evident from temperature rate dependence [3], unusual relaxation dynamics [4], frequency dependence [5], relaxor ferroelectric-like behaviour [6], memory effects in various physical properties of manganite compounds [3, 7]. The existence of phase separation is commonly noticed in these systems, where submicrometer ferromagnetic (FM) metallic and non-ferromagnetic insulating state can coexist. The insulating phase can be either a charged ordered (CO)/orbitally ordered AFM sate or a paramagnetic state. The phase separation (PS) scenario associated with the out of equilibrium state has been reported in the low hole doped and CO manganites. Recently, the magnetotransport properties with the PS scenario has also been reported in the self doped compound, La1−δMnOx, where the interplay among electronic, magnetic, orbital, and structural properties are strongly dependent on δ and x [8, 9]. In case of La deficiency, FM orbitally disordered phase appears in presence of AFM orbitally ordered phase associated with the structural instabilities in La1−δMnOx depending on the values of x [8]. The dynamics of zerofield cooled (ZFC) magnetization as well as in the ac susceptibility have recently been reported indicating the metamagnetic states, which were suggested by the effects of domain wall dynamics in La1−δMnO3 [9, 10]. The extensive studies in the self doped manganites have not been performed as compared to hole doped and CO manganites and it demands special attention because of the intriguing transport and magnetic properties. In this letter, we report mainly on the resistivity (ρ) measurements on La0.87Mn0.98Fe0.02Ox under different conditions of magnetic field and temperature cycling, demonstrating interesting features of field induced metastabilities viz., field cooled (FC) effect, thermal hysteresis, and interesting dynamical features. In addition, we incorporate a simple experimental technique of minor hysteresis loops to identify the phase coexistence in the self doped manganites. The evidence of metastable states in different manganites have been reported quite extensively based on the magnetization studies. However, the examples of such metastable feature in the resistivity measurement are rare, which is reported in this article for self doped manganites. The polycrystalline sample with nominal composition, La0.87Mn0.98Fe0.02Ox was prepared by chemical route [17]. The final heat treatment was performed at 1200 C for 12 h in air, followed by furnace cooling down to room temperature. The magnetoresistance (MR) was measured by standard four-probe technique, fitted with an electromagnet. The magnetization (M) was measured using a commercial superconducting quantum interference device (SQUID) magnetometer. In ZFC measurements of ρ and M , the sample was cooled down to the desired temperature at zero magnetic field and the measurements were performed in the heating cycle with the applied magnetic field. For the FC condition, the sample was cooled down to the desired temperature with magnetic field and the measurements were performed while Magnetic field induced metastability in the self-doped manganites 3 50 100 150 200 250 300 0 2 4 6 8 10 12 14 0 75 150 225 300 0.0 0.3 0.6 0.9 1.2 1.5