A real space description of magnetic field induced melting in the charge ordered manganites: II. The disordered case

Mukherjee, Anamitra; Majumdar, Pinaki

doi:10.1140/epjb/e2014-50233-y

Cited by 3 publications

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References 62 publications

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“…For members of the Ln 1/2 Sr 1/2 MnO 3 family [40][41][42] , with very similar bandwidths, h c increases initially with decreasing BW but takes a downturn beyond a critical BW and then drops to zero, in sharp contrast to the 'divergence' of h c seen in the Ca family. We explain this in terms of the reduced stiffness of the CO state in the presence of disorder 53 .…”

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confidence: 99%

A real space description of magnetic field induced melting in the charge ordered manganites: I. The clean limit

Mukherjee

Majumdar

2014

Eur. Phys. J. B

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We study the melting of charge order in the half doped manganites using a model that incorporates double exchange, antiferromagnetic superexchange, and Jahn-Teller coupling between electrons and phonons. We primarily use a real space Monte Carlo technique to study the phase diagram in terms of applied field (h) and temperature (T ), exploring the melting of charge order with increasing h and its recovery on decreasing h. We observe hysteresis in this response, and discover that the 'field melted' high conductance state can be spatially inhomogeneous even without extrinsic disorder. The hysteretic response plays out in the background of field driven equilibrium phase separation. Our results, exploring h, T , and the electronic parameter space, are backed up by analysis of simpler limiting cases and a Landau framework for the field response. This paper focuses on our results in the 'clean' systems, a companion paper studies the effect of cation disorder on the melting phenomena. c , discussed later) is small. The associated energy scale gµ B h c k B T CO , where T CO is the zero field melting temperature (g is the gyromagnetic ratio and µ B the Bohr magneton). The smallness of h c is attributed to the small energy difference between the CE-CO-I and FM-M states. (ii) The field induced transition is seen to be first order and is accompanied by hysteresis since there are competing metastable minima, particularly for materials close to the CE-CO-I -FM-M phase boundary. (iii) The field induced FM-M is believed to be homogeneous, and is arXiv:0811.3563v4 [cond-mat.str-el]

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Section: Introductionmentioning

confidence: 99%

A real space description of magnetic field induced melting in the charge ordered manganites: I. The clean limit

Mukherjee

Majumdar

2014

Eur. Phys. J. B

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A real space description of magnetic field induced melting in the charge ordered manganites: II. The disordered case

Mukherjee

Majumdar

2014

Eur. Phys. J. B

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We study the effect of A site disorder on magnetic field induced melting of charge order (CO) in half doped manganites using a Monte-Carlo technique. Strong A-site disorder destroys CO even without an applied field. At moderate disorder, the zero field CO state survives but has several intriguing features in its field response. Our spatially resolved results track the broadening of the field melting transition due to disorder and explain the unusual dependence of the melting scales on bandwidth and disorder. In combination with our companion paper on field melting of charge order in clean systems we provide an unified understanding of CO melting across all half doped manganites.

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Conductance switching and inhomogeneous field melting in the charge ordered manganites

2009

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Abstract. -The field induced switching of conductance in the charge ordered half-doped manganites is controlled by the combination of metastability, an inhomogeneous high field state, and cation disorder. We study this non-equilibrium problem via real space Monte Carlo on a disordered strong coupling model appropriate to the manganites. We reproduce the variation of the switching fields with the mean ionic radius rA and cation disorder σA, and demonstrate how the experimental features arise from the proximity of several phases in the Landau free energy landscape. Our prediction for the field melted state is consistent with a growing body of experimental evidence.The manganites owe their fame to the 'colossal magnetoresistance' effect, whereby an applied magnetic field strongly suppresses the resistance of the material. The most extreme version of this happens when the field can actually induce an insulator-metal transition (IMT). This occurs in the low bandwidth half doped manganites, e.g, Pr 0.5 Ca 0.5 MnO 3 , that are typically charge ordered (CO) insulators with CE magnetic order [1][2][3]. The CE-CO-I state is transformed to a ferromagnetic metal (FM-M) by an applied field through a first order phase transition. The magnetic field induced conversion of the CE order to FM, and the crucial resistive switching, involve several subtleties which are only gradually being appreciated [4][5][6][7][8][9][10][11][12][13][14]. These include the surprising difference between the melting fields in two lanthanide (Ln) families, namely the Ca [4] and the Sr [5,6] families; the smallness of the field melting energy scales [4][5][6][7]; and the spatial character of field induced melting and its relation to structural disorder [8][9][10][11][12]. We expand on these issues below.(i) The phase boundary between the CE and FM phase is first order, so metastable states exist on either side. This leads to hysteresis, and the switching fields are decided by non-equilibrium effects, not free energy balance.(ii) While trapping into metastable states is expected in a first order transition, an applied field leads to new equilibrium states which are not simple continuation of the zero field state. In particular, it is increasingly apparent that the field induced conducting state is an inhomogeneous FM-M, a percolative metal with a finite volume fraction of charge ordered regions [8][9][10][11][12]. Finally, (iii) the field induced switching and inhomogeneous metallicity play out on a structurally disordered background. One expects the CO-I state to be more stable in narrow band systems. While this is true in the Ca based manganites [4], where the cation size mismatch σ A is small, it is completely opposite in the Sr based systems [5,6]. The more insulating system can be driven metallic easier in the presence of disorder! These three actors, metastability, field induced inhomogeneity, and pinning disorder, enrich and complicate the field melting problem. There is no understanding of their interplay in the field induced IMT, and the noneq...

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A real space description of magnetic field induced melting in the charge ordered manganites: II. The disordered case

Cited by 3 publications

References 62 publications

A real space description of magnetic field induced melting in the charge ordered manganites: I. The clean limit

A real space description of magnetic field induced melting in the charge ordered manganites: I. The clean limit

A real space description of magnetic field induced melting in the charge ordered manganites: II. The disordered case

Conductance switching and inhomogeneous field melting in the charge ordered manganites

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