We report on the observation of exchange bias (EB) and memory effect in double perovskite Sr 2 FeCoO 6. Antiphase boundaries between the ferromagnetic and the antiferromagnetic regions in the disordered glassy phase are assumed as responsible for the observed effect, which reflects in the cooling field dependence and temperature evolution of exchange bias field and in training effect. The spin glass (SG) phase itself is characterized through memory, ageing, and magnetic relaxation experiments. The spin glass transition temperature, T g, versus H dc 2/3 follows the Almeida-Thouless line yielding a freezing temperature, T f = 73 K. Time-dependent magnetic relaxation studies reveal the magnetization dynamics of the underlying glassy phase in this double perovskite. © 2012 American Institute of Physics.

Sankaranarayanan V

Department Of Physics

Kanikrishnan Sethupathi

R. Pradheesh

ANTIFERROMAGNETIC REGION

Antiphase boundaries

Cooling fields

Double perovskites

Exchange bias

Exchange-bias fields

Freezing temperatures

GLASSY PHASE

Magnetization dynamics

memory Effects

TEMPERATURE EVOLUTION

Time-dependent

Training effects

Antiferromagnetism

Magnetic relaxation

Perovskite

Fulltext

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IIT Madras

Applied Physics Letters

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 temperature dependent structural studies carried out on the spin-correlated system A2FeCoO6 (A= Sm, Eu, Dy and Ho) or AFCO (A= Sm, E, D and H), using synchrotron radiation is presented. Owing to the large absorption cross-sections of the rare earths; Eu, Sm and Dy for neutrons, synchrotron radiation is one of the best available candidates for probing the system. The perovskite phase formation is inferred from laboratory XRD with Cu Kα source. The temperature dependent synchrotron X-ray diffraction (SXRD) experiments show the coexistence of monoclinic P21/n and orthorhombic Pbnm phases in Ho and Dy, while Eu and Sm are formed in single phase Pbnm. The temperature dependent DC magnetization measurements infer the presence of many interesting features such as thermal hysteresis, magnetic irreversibility, spin re-orientation, re-entrant magnetization and negative magnetization. © 2017 Author(s).

AIP Advances

Temperature dependent structural studies on the spin correlated system A2FeCoO6 (A= Sm, Eu, Dy and Ho) using synchrotron radiation

Unusual features in magnetization resembling the kinetic arrest of a magnetic glass state are observed in the La-doped double perovskite, SrLaFeCoO6. Neutron powder diffraction experiments confirm the presence of antisite disorder as well as a lack of long-range magnetic order down to 4 K in this double perovskite which displays spin glass-like features in dc and ac susceptibilities. Magnetic relaxation observed through cooling and heating under unequal fields (CHUF) point towards unusual domain dynamics which is supported by a broad memory effect. Among the two anomalies that are observed at 75 K and at 250 K in the magnetic measurements, the former is associated with a spin-freezing temperature below which the magnetic glass state is experimentally verified. The magnetometric experiments detailed in the paper bring out the non-equilibrium metastable magnetic states in this disordered magnetic system. The magnetic glass state described above manifests in the electrical resistivity through the formation of a 'hard gap' because of the spin-exchange energy following the formation of magnetic glass. It is observed that the combination of disorder and magnetic glass state leads to a large, negative magnetoresistance (MR) of ≈47 at 5 K in 8 T. © 2017 IOP Publishing Ltd.

Journal of Physics Condensed Matter

Magnetic glass state and magnetoresistance in SrLaFeCoO6 double perovskite

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

Integrated Environmental Assessment and Management

Impact of nuclear accidents on marine biota

Nature Materials

A spin-valve-like magnetoresistance of an antiferromagnet-based tunnel junction

Journal of Physics: Condensed Matter

Exchange bias effect in alloys and compounds

Simultaneous enhancement of anisotropy and grain isolation inCoPtCr-SiO2perpendicular recording media by a MnRu intermediate layer

Exchange bias and memory effect in double perovskite Sr 2FeCoO 6

Journal	Applied Physics Letters
ISSN	00036951
Open Access	No