Neutron diffraction measurement on the spin glass double perovskite Sr2FeCoO6 reveals site disorder as well as Co3+ intermediate spin state. In addition, multiple valence states of Fe and Co are confirmed through M̈ossbauer and X-ray photoelectron spectroscopy. The structural disorder and multiple valence lead to competing ferromagnetic and antiferromagnetic interactions and subsequently to a spin glass state, which is reflected in the form of an additional T-linear contribution at low temperatures in specific heat. A clear evidence of Jahn-Teller distortion at the Co3+-O6 complex is observed and incorporating the physics of Jahn-Teller effect, the presence of localized magnetic moment is shown. A large, negative and anomalous magnetoresistance of ≈63% at 14 K in 12 T applied field is observed for Sr2FeCoO6. The observed magnetoresistance could be explained by applying a semi-empirical fit consisting of a negative and a positive contribution and show that the negative magnetoresistance is due to spin scattering of carriers by localized magnetic moments in the spin glass phase. © Springer-Verlag 2012.

Sankaranarayanan V

Department Of Physics

Kanikrishnan Sethupathi

R. Pradheesh

Applied field

Double perovskites

Ferromagnetic and anti-ferromagnetic

INTERMEDIATE SPINS

LOCALIZED MAGNETIC MOMENTS

Low temperatures

MULTIPLE VALENCE STATE

Negative magneto-resistance

Neutron diffraction measurements

Semi-empirical

SITE DISORDER

Spin glass state

SPIN SCATTERING

SPIN-GLASS PHASE

Structural disorders

Antiferromagnetism

Electric resistance

Jahn-Teller effect

Magnetic moments

Neutron diffraction

Perovskite

Photoelectrons

X ray photoelectron spectroscopy

Magnetoresistance

Fulltext

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IIT Madras

European Physical Journal B

The magnetism of the double perovskite compounds La2-xSrxFeCoO6 (x=0,1,2) is contrasted using magnetization, neutron diffraction, and electron paramagnetic resonance with the support from density functional theory calculations. La2FeCoO6 is identified as a long-range ordered antiferromagnet displaying a near-room temperature transition at TN=270 K, accompanied by a low temperature structural phase transition at TS=200 K. The structural phase transformation at TS occurs from R3̄c at 300 K to Pnma at 200 K. The density functional theory calculations support an insulating noncompensated antiferromagnetic structure. The long-range ordered magnetism of La2FeCoO6 transforms to short-range glassy magnetism as La is replaced with Sr in the other two compounds. The magnetism of La2FeCoO6 is differentiated from the nonequilibrium glassy features of Sr2FeCoO6 and SrLaFeCoO6 using the cooling-and-heating-in-unequal-fields magnetization protocols. This contrasting magnetism in the La2-xSrxFeCoO6 series is evidenced in electron paramegnetic resonance studies. The electronic density of states estimated using the density functional theory calculations contrast the insulating feature of La2FeCoO6 from the metallic nature of Sr2FeCoO6. From the present suite of experimental and computational results on La2-xSrxFeCoO6, it emerges that the electronic degrees of freedom, along with antisite disorder, play an important role in controlling the magnetism observed in double perovskites. © 2019 American Physical Society.

Physical Review B

Contrasting the magnetism in La2-xSrxFeCoO6 (x=0,1,2) double perovskites: The role of electronic and cationic disorder

The study of hyperfine interaction by high-resolution inelastic neutron scattering is not very well known compared to the other competing techniques viz. nuclear magnetic resonance, Mössbauer, perturbed angular correlation spectroscopy, etc. Also, studies have been limited mostly to magnetically ordered systems. Here, we report such a study on Sr2-xLaxFeCoO6 (x=0,1,2) of which the first (Sr2FeCoO6 with x=0) has a canonical spin-glass state, the second (SrLaFeCoO6 with x=1) has a so-called magnetic glass state, and the third (La2FeCoO6 with x=2) has a magnetically ordered ground state. Our present study revealed a clear inelastic signal for SrLaFeCoO6, a possible inelastic signal for Sr2FeCoO6 below the spin freezing temperatures Tsf, but no inelastic signal at all for the magnetically ordered La2FeCoO6 in the neutron-scattering spectra. The broadened inelastic signals observed suggest hyperfine field distributions in the two disordered magnetic glassy systems, whereas the absent inelastic signal for the third compound suggests no, or a very small, hyperfine field at the Co nucleus due to Co electronic moment. The hyperfine splitting on the Co nucleus is induced by the electronic spin state of the magnetic sample atom, and our experiments add information concerning the timescale of electronic spin fluctuations by the appearance of quasielastic broadening in the μeV range at low Q and spin freezing on the nanosecond timescale below Tsf. Whereas these features are observed at low Q for x=0 and 1, they are absent for La2FeCoO6, which evidences a gradual increase of the elastic intensity only at large Q near an emerging Bragg peak. Thus both electronic magnetic spin freezing and inelastic excitations arising from nuclear hyperfine splitting at the Co site consistently indicate a different behavior for x=2. © 2018 American Physical Society.

Hyperfine interaction and electronic spin fluctuation study on Sr2-xLaxFeCoO6 (x = 0, 1, 2) by high-resolution backscattering neutron spectroscopy

A spin glass state is observed in the double perovskite oxide Sr 2FeCoO 6 prepared through sol-gel technique. Initial structural studies using x rays reveal that the compound crystallizes in tetragonal I4/m structure with lattice parameters, a 5.4609(2) Å and c 7.7113(7) Å. The temperature dependent powder x ray diffraction data reveal no structural phase transition in the temperature range 10-300 K. However, the unit cell volume shows an anomaly coinciding with the magnetic transition temperature thereby suggesting a close connection between lattice and magnetism. Neutron diffraction studies and subsequent bond valence sums analysis show that in Sr 2FeCoO 6, the B site is randomly occupied by Fe and Co in the mixed valence states of Fe 3+/Fe 4+ and Co 3+/Co 4+. The random occupancy and mixed valence sets the stage for inhomogeneous magnetic exchange interactions and in turn, for the spin glass state in this double perovskite, which is observed as an irreversibility in temperature dependent dc magnetization at T f ∼ 75 K. Dynamical scaling analysis of ′(T) yields a critical temperature T ct 75.14(8) K and an exponent z 6.2(2) typical for spin glasses. The signature of presence of mixed magnetic interactions is obtained from the thermal hysteresis in magnetization of Sr 2FeCoO 6. Combining the neutron and magnetization results of Sr 2FeCoO 6, we deduce that Fe is in low spin state while Co is in both low spin and intermediate spin states. © 2012 American Institute of Physics.

Journal of Applied Physics

Observation of spin glass state in weakly ferromagnetic Sr 2FeCoO 6 double perovskite

Physics Today

arXiv adds category for applied physics

Spin Glasses

European Review of Aging and Physical Activity

Editorial

J. Mater. Chem.

Cobalt-based double-perovskite symmetrical electrodes with low thermal expansion for solid oxidefuel cells

Large magnetoresistance and Jahn-Teller effect in Sr2FeCoO6

Journal	European Physical Journal B
ISSN	14346028
Open Access	No