Field-induced avalanche to the ferromagnetic state in the phase-separated ground state of manganites

Abstract

Perovskite manganite compounds such as Pr1−x(Ca1−ySry)xMnO3 can be tuned to exhibit a metastable ground state where two magnetic/crystallographic phases coexist in zero magnetic field. Field-dependent neutron diffraction measurements on both poly-and single-crystal samples with a range of Pr, Ca, and Sr dopings(0.3≤x≤0.35 and y≤0.30) reveal that the charge-ordered, antiferromagnetic phase of the ground state suddenly and irreversibly jumps to the ferromagnetic state. The transition occurs spontaneously at some time after the field is set above a threshold field, indicating that once the transition is initiated an avalanche occurs that drives it to completion. [3,4,5,6] and computational results [7] indicate the phases are arranged as FM domains embedded in a CO/AFM matrix. The delicate energy balance that exists between these phases is easily tipped by external perturbations such as magnetic field [6,8,9], electric field[10], electron[11] or x-ray irradiation [12], which destroy the CO/AFM phase and drive the system irreversibly into the FMM state.A model system for such phase-separated behavior is the hole-doped Pr 1−x Ca x MnO 3 (PCMO) system in the range x=0.3-0.45 [13,14,15], which can be fine-tuned by additional substitutions such as Sr for Ca, Co for Mn, or Ga for Mn [6]. An applied field gradually converts the AFM phase to the FMM phase as expected, but recent low temperature isothermal magnetization M(H) data for these PCMO compounds reveal novel jumps in the magnetization that occur at discrete threshold fields [16,17,18,19]. The rapid onset of these jumps at low temperatures and their appearance in polycrystalline samples rule out the usual phenomena such as spin-flop or metamagnetic transitions; such transitions are only sharp for a narrow range of field directions with respect to atomic spin directions in the crystal, and they do not exhibit a sudden onset at low T (well below the magnetic ordering temperature) [20]. To investigate the microscopic origin of these jumps in the magnetization, we have carried out field-dependent neutron diffraction and inelastic measurements on both polycrystalline and single crystal samples. We find that at low T both the charge and antiferromagnetic order parameters suddenly and irreversibly collapse above a threshold field, with a concomitant jump in the ferromagnetic order parameter. Our results indicate that there are two important factors leading to this unique behavior. One is the remarkable isotropy of the ferromagnetic system, which makes the internal magnetic energy, to a very good approximation, independent of crystallographic direction. The second factor concerns the lattice strain [21,22] that develops at the boundaries between the FM and CO/AFM phases. This strain inhibits the smooth growth of FM domains, resulting in a stick-slip growth of domains. When one of the distorted CO/AFM domains does transform to the FMM phase, the net magnetization in the vicinity of this new FMM domain subsequently jumps, causing other CO/AFM regions to convert in an avalanc...

Magnetism in gallium-dopedCeFe2: Martensitic scenario

“…[14][15][16][17][18][19][20] Among the intermetallics, Gd 5 Ge 4 is known to show many similarities with the oxides. 11,23 Though there are several factors thought to be responsible for the multistep behavior, the most striking and accepted reason common to the oxide materials and the intermetallics seems to be the martensitic transition driven by the applied field.…”

“…11 Interestingly, single-step and multistep magnetization behaviors are observed in some mixed-valent manganites showing colossal magnetoresistance ͑CMR͒, even in polycrystalline form. [12][13][14][15][16][17][18][19][20] Basically, these materials are phaseseparated systems, and the transformation between the two phases has a martensitic character. In addition to the AFM-FM transition, it has been found that the breakdown of charge and orbital ordering also leads to the magnetization jumps in the case of manganites, in general.…”

Melting of magnetic correlations in charge-orbital orderedLa1/2Sr3/2MnO4Senff1, Schumann2, Benomar3 et al. 2008Phys. Rev. B232280View full textAdd to dashboardCite

“…1 The larger part of it seems to arise from the competition between ferromagnetic ͑FM͒ metallic and charge ordered insulating states, and recent experimental and theoretical investigations focus on electronically soft phases and phase separation scenarios. [2][3][4][5][6] The metalinsulator transition can be considered as the stabilization of the FM metallic phase over charge ordered insulating states by an external parameter as, e.g., temperature or magnetic field. 7,8 At half doping, the insulating, charge-orbital ordered ͑COO͒ phase appears most stable, and an ordered state appears as a generic feature in the phase diagrams of cubic manganites R 1−x A x MnO 3 ͑R = La or rare earth, A =Sr,Ba,Ca,…͒, 7 as well as in those of single-and double-layered systems, such as La 1/2 Sr 3/2 MnO 4 and LaSr 2 Mn 2 O 7 .…”

“…9,[33][34][35][36] Magnetic ordering of the CE type occurs below T N = 110 K. 9 Compared to the perovskite manganites, the COO state is exceptionally stable in La 1/2 Sr 3/2 MnO 4 and only very high fields of the order of 30 T can melt the ordered state, implying negative magnetoresistance effects. 37 Good metallic properties are, however, never achieved in the single-layered manganites La 1−x Sr 1+x MnO 4 neither by magnetic field nor by doping. 38,39 In a recent work, we have studied the magnetic excitation spectrum of the CE-type ordering in La 1/2 Sr 3/2 MnO 4 at low temperatures.…”

Magnetostructural transition in Ce(Fe0.975Ga0.025)2 compound

“…[1][2][3][4][5][6][7][8][9][10][11][12] Among various materials, doped CeFe 2 compounds have evinced the above features of the first order transition rather convincingly. [11][12][13][14] The occurrence of these exotic properties is believed to be a consequence of the magnetostructural transition.…”