Antisite Disorder-induced Exchange Bias Effect in Multiferroic Y2CoMnO6
TL;DR: The role of antisite disorder in creating the domain structure leading to exchange bias effect is highlighted in this paper, where 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.
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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TL;DR: The synthesized series of the double-perovskite R2CoMnO6 single crystals offer comprehensive information for understanding the roles of mixed-valent magnetic ions and rare earth magnetic moments on the magnetic properties.
Abstract: We have successfully synthesized the series of the double-perovskite R2CoMnO6 (R = rare earth: La to Lu) single crystals and have investigated their magnetic properties. The ferromagnetic order of Co(2+)/Mn(4+) spins emerges mainly along the c axis. Upon decreasing the size of rare earth ion, the magnetic transition temperature decreases linearly from 204 K for La2CoMnO6 to 48 K for Lu2CoMnO6, along with the enhancement of monoclinic distortion. The temperature and magnetic-field dependences of magnetization reveal the various magnetic characteristics such as the metamagnetic transition in R = Eu, the isotropic nature of rare earth moment in R = Gd, and the reversal of magnetic anisotropy in R = Tb and Dy. Our results offer comprehensive information for understanding the roles of mixed-valent magnetic ions and rare earth magnetic moments on the magnetic properties.
44 citations
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.
36 citations
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.
35 citations
TL;DR: In this article, a phenomenological model has been proposed to explain the exchange coupling between the ferromagnetic and canted-antiferromagnetic interfaces of antisite-disordered double perovskite La 1.5 Ca 0.5 CoMnO 6 mainly on the basis of uncompensated interface spins.
33 citations
TL;DR: In this paper, the antisite disorder in the antiferromagnetic double perovskite (LaSrCoFeO) lattice was studied and the effect of such disorder induced a spin-glass state in the lattice.
Abstract: Antisite (B-site) disorder in double perovskite lattice is responsible for various magnetic phenomena such as exchange bias, spin glass, memory effect, colossal magnetoresistance, etc. By controlling the antisite disorder in the antiferromagnetic double perovskite ${\mathrm{LaSrCoFeO}}_{6}$, we achieve intrinsic exchange bias effect with a large exchange bias field ($\ensuremath{\sim}1.2$ kOe) and giant coercive field ($\ensuremath{\sim}12.8$ kOe). Further, we find that the effect of such antisite disorder induces a spin-glass state in ${\mathrm{LaSrCoFeO}}_{6}$. Multiple signatures of slow dynamics were confirmed by frequency-dependent peak shift, slow spin relaxation, and memory effect over a wide temperature regime ($5\ensuremath{-}80$ K). The AC susceptibility data near the spin-glass temperature ($\ensuremath{\sim}72.1\ifmmode\pm\else\textpm\fi{}0.6$ K) are best fit by a critical slowing down model described by a dynamical exponent $\mathrm{z}\ensuremath{
u}=7.5\ifmmode\pm\else\textpm\fi{}0.5$ and ${\ensuremath{\tau}}_{0}=1.05\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}12}$ s. The origin of exchange bias and spin glass are briefly discussed.
32 citations
References
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21 May 2003
TL;DR: How the memory operates is described, including significant aspects of reading, writing, and integration of the magnetic material with CMOS, which enabled the recent demonstration of a 1-Mbit memory chip.
Abstract: Magnetoresistive random access memory (MRAM) technology combines a spintronic device with standard silicon-based microelectronics to obtain a combination of attributes not found in any other memory technology. Key attributes of MRAM technology are nonvolatility and unlimited read and write endurance. Magnetic tunnel junction (MTJ) devices have several advantages over other magnetoresistive devices for use in MRAM cells, such as a large signal for the read operation and a resistance that can be tailored to the circuit. Due to these attributes, MTJ MRAM can operate at high speed and is expected to have competitive densities when commercialized. In this paper, we review our recent progress in the development of MTJ-MRAM technology. We describe how the memory operates, including significant aspects of reading, writing, and integration of the magnetic material with CMOS, which enabled our recent demonstration of a 1-Mbit memory chip. Important memory attributes are compared between MRAM and other memory technologies.
471 citations
TL;DR: The phenomenology of exchange bias effects observed in structurally single-phase alloys and compounds but composed of a variety of coexisting magnetic phases such as ferromagnetic, antiferromagnetic.
Abstract: The phenomenology of exchange bias effects observed in structurally single-phase alloys and compounds but composed of a variety of coexisting magnetic phases such as ferromagnetic, antiferromagnetic, ferrimagnetic, spin-glass, cluster-glass and disordered magnetic states are reviewed. The investigations on exchange bias effects are discussed in diverse types of alloys and compounds where qualitative and quantitative aspects of magnetism are focused based on macroscopic experimental tools such as magnetization and magnetoresistance measurements. Here, we focus on improvement of fundamental issues of the exchange bias effects rather than on their technological importance.
348 citations
TL;DR: In this article, the authors reported the observation of exchange bias in bulk polycrystalline Ni50Mn25+xSb25−x Heusler alloys and attributed it to the coexistence of antiferromagnetic and ferromagnetic exchange interactions in the system.
Abstract: The authors report the observation of exchange bias in bulk polycrystalline Ni50Mn25+xSb25−x Heusler alloys. Shifts in hysteresis loops of up to 248Oe were observed in the 5T field cooled samples. The observed exchange bias behavior in Ni50Mn25+xSb25−x is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions in the system. Such behavior is an addition to the multifunctional properties of the Ni50Mn25+xSb25−x Heusler alloy system.
237 citations
TL;DR: The magnetic properties of ferromagnetic-antiferromagnetic Co-CoO core-shell nanoparticles are investigated as a function of the in-plane coverage density and the superparamagnetic blocking temperature, the coercivity, and the bias field radically increase with increasing coverage.
Abstract: The magnetic properties of ferromagnetic-antiferromagnetic Co-CoO core-shell nanoparticles are investigated as a function of the in-plane coverage density from 3.5% to 15%. The superparamagnetic blocking temperature, the coercivity, and the bias field radically increase with increasing coverage. This behavior cannot be attributed to the overall interactions between cores. Rather, it can be semiquantitatively understood by assuming that the shells of isolated core-shell nanoparticles have strongly degraded magnetic properties, which are rapidly recovered as nanoparticles come into contact.
193 citations
TL;DR: In this article, the Ni50Mn36Sn14 Heusler alloy was observed to have exchange bias after field cooling by means of hysteresis loop measurement and its magnitude significantly increased with decreasing temperature below 70K.
Abstract: Exchange bias was observed in the Ni50Mn36Sn14 Heusler alloy after field cooling by means of hysteresis loop measurement. The hysteresis loops shift along the axis of an applied field and its magnitude significantly increased with decreasing temperature below 70K. This effect could be understood as a result of exchange anisotropy created at the interface between an antiferromagnet and a ferromagnet in the phase separated of martensitic state. Above 70K, however, the exchange bias field disappeared and the coercivity significantly reduced owing to the fact that the pinning between an antiferromagnet and a ferromagnet becomes weaker with increasing temperature.
160 citations