Visible range colossal magnetorefractive effect in (La_{1 −y}Pr_y)_2/3Ca_1/3MnO₃films

Abstract

We report a colossal magnetorefractive effect (MRE) in epitaxial thin films of a classical colossal magnetoresistance (CMR) manganite, (La 1 − y Pr y ) 2/3 Ca 1/3 MnO 3 (y = 0.375 and 0.7). Close to the ferromagnetic (FM) phase transition a moderate applied magnetic field, H ∼ 10 kOe, results in a reduction of the optical reflectance by ∼18% for the photon energy E ∼ 2.7 eV. The MRE spectral behavior with three pronounced maxima at E = 1.6, 2.7 and 4.0 eV points out an inter-site nature of the involved optical transitions. The results are discussed within a phase separation scenario with coexisting FM metallic nanodomains antiferromagnetically coupled by correlated polarons. The probability of MRE optical transitions is maximal for antiparallel alignment of Mn 3+ /Mn 4+ -spins realized for the coercive field, H c ∼ 200-800 Oe, and is suppressed by stronger fields, which favor FM metallic behavior. As a result, both the optical reflectivity and the electrical resistance decrease, yielding a close similarity between the CMR and MRE behavior.ferromagnetic-paramagnetic (FM-PM) as well as structural phase transitions. It is commonly believed that strong electronic and spin correlations together with the electron-phonon coupling are responsible for a rich phase diagram containing different electronic, magnetic and structural phases [2]. In addition, these transitions can be strongly influenced by external (hydrostatic pressure, magnetic and electric fields, electromagnetic radiation) and internal (chemical pressure, doping) control parameters, leading to drastic changes in the magnetotransport. To explain the huge reduction of the electrical resistance in an applied field of a few tesla, e.g. CMR = (R(0)-R(B))/R(B) = 10 5 -10 8 , an electronic phase separation (EPS) scenario was proposed [2,3]. Close to the Curie temperature, T C , the coexisting FM metallic and chargeordered insulating (COI) phases may have a similar free energy, so that a relatively low applied magnetic field, favoring the FM-phase, may cause the MI transition due to the formation of percolating paths of the metallic phase through the sample [2,[4][5][6]. Very recently [7] we have shown that EPS in thin films of a classical CMR manganite, i.e. (La 1 − y Pr y ) 2/3 Ca 1/3 MnO 3 (LPCMO) with Pr-doping, y ∼ 0.4, develops at the nanometer scale, where FM nanodomains are intrinsically antiferromagnetic (AFM) exchange coupled by correlated Jahn-Teller (JT) polarons. The latter, dubbed in the literature as 'polaronic phase' or 'correlated polarons', have been experimentally detected by neutron scattering [8,9] and x-ray diffraction [10] in the form of short-range-ordered lattice superstructures of CE-type with correlation length 1-2 nm. By means of isovalent substitution of a large La 3+ cation by a smaller Pr 3+ in the optimally holedoped La 2/3 Ca 1/3 MnO 3 (LCMO) an increase of electron-phonon interaction favors the tendency to phase competition [11]. The FM metallic ground state for y = 0 progressively transforms with increasing 'y' into a mixture of FM...

Polaronic Emergent Phases in Manganite-based Heterostructures

“…Summarizing, the small size of FM nanodomains, R FM ∼ 6-8 nm, in compositionally tuned LPCMO with relatively strong electron-phonon coupling taken together with the estimated coupling constant, J AFM = 4.5 × 10 4 J/m 2 , provide a rational solution of the long-standing issue in CMR physics, i.e., how a tiny amount of CPs can be responsible for extremely large magnetic-field-induced changes in electrical resistance. Note, that colossal effects are not limited to CMR, very large and hysteretic field-induced changes of refractive index [8] and of the elastic moduli [9] were also observed in LPCMO.…”

“…In addition, the spin-ordered insulating phases can be charge and/or orbital ordered (COO) at low temperatures. It is due to the phase transitions and strong spin-spin, spin-phonon, and electron-phonon couplings that strongly correlated oxides display drastic changes in electrical resistivity, called as colossal magnetoresistance [6,7] (CMR) as well as in optical and elastic properties, dubbed "colossal magnetorefractive" [8] and "colossal magnetoelastic" [9] effects, respectively.…”

Особенности поглощения тонких пленок La-=SUB=-0.69-=/SUB=-Ba-=SUB=-0.31-=/SUB=-MnO-=SUB=-3-delta-=/SUB=-, полученных методом импульсного лазерного осаждения

“…Исследования магнитооптических (МО) эффектов в сильнокоррелированных соединениях на основе допированных манганитов лантана обычно ограничиваются эффектами Фарадея и Керра, магнитного кругового или линейного дихроизма в области фундаментального поглощения и диапазоном температур вблизи магнитного фазового перехода ферромагнетик/парамагнетик, который, как правило, находится ниже комнатной температуры [1][2][3]. Внешнее магнитное поле влияет на процессы взаимодействия света с примесными состояниями, локализованными и делокализованными носителями заряда в инфракрасном (ИК) диапазоне, что дает основной вклад в магнитотранспортные и МО свойства допированных манганитов.…”

Features of absorption of thin films La-=SUB=-0.69-=/SUB=-Ba-=SUB=-0.31-=/SUB=-MnO-=SUB=-3-delta-=/SUB=- obtained using the method of pulsed laser deposition

“…Studies of magneto-optical (MO) effects in strongly correlated compounds based on doped lanthanum manganites are usually limited by the Faraday and Kerr effects, magnetic circular or linear dichroism in the fundamental absorption region, and the temperature range near the ferromagnet/paramagnet magnetic phase transition, which, as a rule, is below room temperature [1][2][3]. An external magnetic field affects the processes of interaction of light with impurity states, localized and delocalized charge carriers in the infrared (IR) range, which makes the main contribution to the magnetotransport and MO properties of doped manganites.…”