Journal ArticleDOI

# Magnetization-steps in Y2CoMnO6 double perovskite: The role of antisite disorder

24 Sep 2014-Journal of Applied Physics (AIP Publishing LLCAIP Publishing)-Vol. 116, Iss: 12, pp 123907
Abstract: Antisite disorder is observed to have significant impact on the magnetic properties of the double perovskite Y2CoMnO6 which has been recently identified as a multiferroic. A paramagnetic-ferromagnetic phase transition occurs in this material at Tc ≈ 75 K. At 2 K, it displays a strong ferromagnetic hysteresis with a significant coercive field of Hc ≈ 15 kOe. Sharp steps are observed in the hysteresis curves recorded below 8 K. In the temperature range 2 K ≤ T ≤ 5 K, the hysteresis loops are anomalous as the virgin curve lies outside the main loop. The field-cooling conditions as well as the rate of field-sweep are found to influence the steps. Quantitative analysis of the neutron diffraction data shows that at room temperature, Y2CoMnO6 consists of 62% of monoclinic P21/n with nearly 70% antisite disorder and 38% Pnma. The bond valence sums indicate the presence of other valence states for Co and Mn which arise from disorder. We explain the origin of steps by using a model for pinning of magnetization at the antiphase boundaries created by antisite disorder. The steps in magnetization closely resemble the martensitic transformations found in intermetallics and display first-order characteristics as revealed in the Arrott's plots.
Topics: Magnetization (55%), Magnetic hysteresis (52%), Phase transition (51%), Ferromagnetism (51%), Coercivity (51%)
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, Lin Qin1, Shala Bi1
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Journal ArticleDOI
Harikrishnan S. Nair
Abstract: Exchange bias effect in the ferromagnetic double perovskite compound Y2CoMnO6, which is also a multiferroic, is reported. The exchange bias, observed below 8 K, is explained as arising due to the interface effect between the ferromagnetic and antiferromagnetic clusters created by antisite disorder in this material. Below 8 K, prominent ferromagnetic hysteresis with metamagnetic “steps” and significant coercive field, Hc ≈ 10 kOe are observed in this compound which has a Tc ≈ 75 K. A model based on growth of ferromagnetic domains overcoming the elastic energy of structurally pinned magnetic interfaces, which closely resembles martensitic-like transitions, is adapted to explain the observed effects. The role of antisite disorder in creating the domain structure leading to exchange bias effect is highlighted in the present work.

38 citations

Journal ArticleDOI
Harikrishnan S. Nair
Abstract: Exchange bias effect in the ferromagnetic double perovskite compound Y$_2$CoMnO$_6$, which is also a multiferroic, is reported. The exchange bias, observed below 8~K, is explained as arising due to the interface effect between the ferromagnetic and antiferromagnetic clusters created by {\it antisite} disorder in this material. Below 8~K, prominent ferromagnetic hysteresis with metamagnetic "steps" and significant coercive field, $H_c \approx$ 10~kOe are observed in this compound which has a $T_c \approx$ 75~K. A model based on growth of ferromagnetic domains overcoming the elastic energy of structurally pinned magnetic interfaces, which closely resembles martensitic-like transitions, is adapted to explain the observed effects. The role of {\it antisite} disorder in creating the domain structure leading to exchange bias effect is highlighted in the present work.

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Journal ArticleDOI

TL;DR: Magnetic and dielectric properties of the double perovskite Ho2NiMnO6 are reported and signs of inherent Griffiths phase pertaining to the Ni/Mn subsystem are visible.
Abstract: Magnetic and dielectric properties of the double perovskite Ho2NiMnO6 are reported. The compound is synthesized by nitrate route and is found to crystallize in monoclinic P2(1)/n space group. Lattice parameters obtained by refining powder x-ray diffraction data are; a = 5.218(2)angstrom, b = 5.543(2)angstrom, c = 7.480(3)angstrom and the monoclinic angle i beta = 90.18 degrees(4). A phase transition is observed at T-C = 86 K in the temperature-dependent magnetization curve, M(T). The inverse magnetic susceptibility, (1/chi(T)) fits reasonably well with modified Curie-Weiss law by incorporating the paramagnetic response of Ho3+. 1/chi(T) manifests as an upward deviation from ideal Curie-Weiss behaviour well above the ferromagnetic transition. Signs of inherent Griffiths phase pertaining to the Ni/Mn subsystem are visible when one subtracts the Ho3+ paramagnetic contribution from total susceptibility and does the power-law analysis. The magnetic hysteresis at 2 K gives the maximum value of magnetization M-max approximate to 15 mu(B)/f. u. at 50 kOe. Field-derivative of magnetization at 2 K shows discontinuities which indicates the existence of metamagnetic transitions in this compound. This needs to be probed further. Out of the two dielectric relaxations observed, the one at low temperature may be attributed to phononic frequencies and that at higher temperature may be due to Maxwell-Wagner relaxation. A correlation between magnetic and lattice degrees of freedom is plausible since the anomaly in dielectric constant coincides with T-C.

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Journal ArticleDOI

TL;DR: The structural, magnetic, electrical and dielectric properties of an Ir-based double perovskite compound, La2CoIrO6, have been investigated and it is shown that a clear magnetodielectric coupling effect exists in La2 coirO6 at low temperatures.
Abstract: The structural, magnetic, electrical and dielectric properties of an Ir-based double perovskite compound, La2CoIrO6, have been investigated. The sample undergoes a paramagnetic-ferromagnetic transition at TC, followed by a reentrant spin-glass transition at lower temperatures. The reentrant spin glass state in La2CoIrO6 is associated with the competitions of the antiferromagnetic coupling between Ir4+ and Co2+ ions and the ferromagnetic clusters. La2CoIrO6 shows a semiconducting transport behavior in the temperature range 65 to 360 K and the transport behavior can be well described by the three-dimensional Mott variable range hopping conduction mechanism. Moreover, a strong frequency dependence of dielectric constant behavior for La2CoIrO6 is observed and the dielectric relaxation can be ascribed to the electron hopping between different transition metal ions. In addition, the isothermal magnetic field dependent dielectric constant measurements show that a clear magnetodielectric coupling effect exists in La2CoIrO6 at low temperatures.

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Abstract: The relation between the symmetry of electron orbitals and superexchange interaction is discussed. It is shown that the sign of the superexchange interaction is closely connected with the cation orbital state, when the cation is subject to the crystalline field arising from octahedrally or tetrahedrally surrounding anions. In some cases, the sign of the superexchange interaction is definitely determined from the symmetry relations. The cases in which each cation is subject to an octahedral cubic field and the lines connecting the interacting cations to the intervening anion make an angle of either 180° or 90° are discussed in particular. Our discussion of the 180° case is applicable to crystals of the perovskite type and NaCl type and that of the 90° case to anhydrous chlorides. In the case where each cation is subject to a tetrahedral cubic field, there is a definite relation between the symmetry of the cation electron orbitals and superexchange interaction, if only the s -orbital of anion participates in the superexchange interaction. TiH 2 is an example of this case. The interaction between nearest-neighbor cations in the crystal of the NaCl type is also discussed.

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