Spin reorientation and disordered rare earth magnetism in Ho$_2$FeCoO$_6$
TL;DR: The experimental observation of spin reorientation in the double perovskite Ho2FeCoO6 is reported, and it is seen that only short-range magnetic order prevails in Ho3+ - lattice.
Abstract: We report the experimental observation of spin reorientation in the double perovskite Ho$_2$FeCoO$_6$. The magnetic phase transitions in this compound are characterized and studied through magnetization and specific heat, and the magnetic structures are elucidated by neutron powder diffraction. Two magnetic phase transitions are observed in this compound - one at $T_\mathrm{N1} \approx$ 250~K, from paramagnetic to antiferromagnetic, and the other at $T_\mathrm{N2} \approx$ 45~K, from a phase with mixed magnetic structures to a single phase through a spin reorientation process. The magnetic structure in the temperature range 200~K - 45~K is a mixed phase of the irreducible representations $\Gamma_1$ and $\Gamma_3$, both of which are antiferromagnetic. The phase with mixed magnetic structures that exists in Ho$_2$FeCoO$_6$ gives rise to a large thermal hysteresis in magnetization that extends from 200~K down to the spin reorientation temperature. At $T_\mathrm{N2}$, the magnetic structure transforms to $\Gamma_1$. Though long-range magnetic order is established in the transition metal lattice, it is seen that only short-range magnetic order prevails in Ho$^{3+}$ - lattice. Our results should motivate further detailed studies on single crystals in order to explore spin reorientation process, spin switching and the possibility of anisotropic magnetic interactions giving rise to electric polarization in Ho$_2$FeCoO$_6$.
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TL;DR: The magnetic spin ordering and the magnetization dynamics of a double perovskite Pr2CoFeO6 have been investigated by employing the (dc and ac) magnetization and neutron powder diffraction techniques as discussed by the authors.
Abstract: The magnetic spin ordering and the magnetization dynamics of a double perovskite Pr2CoFeO6 have been investigated by employing the (dc and ac) magnetization and neutron powder diffraction techniques. The study revealed that Pr2CoFeO6 adopted a B-site disordered orthorhombic structure (Pnma). Furthermore, ab initio band structure calculations suggested an insulating antiferromagnetic ground state. Magnetization measurements revealed that the system possesses a spectrum of competing magnetic phases, viz., long range canted antiferromagnetic (AFM) spin ordering (TN ∼ 269 K), Griffiths-like phase, re-entrant cluster glass (TG ∼ 34 K), and exchange bias effects. The neutron diffraction study divulged the exhibition of a long range G-type of canted AFM spin ordering. The random nonmagnetic dilution of magnetic Fe3+ (high spin) ions by Co3+ (low spin) ions due to B-site disorder essentially played a crucial role in manifesting such magnetic properties of the system.The magnetic spin ordering and the magnetization dynamics of a double perovskite Pr2CoFeO6 have been investigated by employing the (dc and ac) magnetization and neutron powder diffraction techniques. The study revealed that Pr2CoFeO6 adopted a B-site disordered orthorhombic structure (Pnma). Furthermore, ab initio band structure calculations suggested an insulating antiferromagnetic ground state. Magnetization measurements revealed that the system possesses a spectrum of competing magnetic phases, viz., long range canted antiferromagnetic (AFM) spin ordering (TN ∼ 269 K), Griffiths-like phase, re-entrant cluster glass (TG ∼ 34 K), and exchange bias effects. The neutron diffraction study divulged the exhibition of a long range G-type of canted AFM spin ordering. The random nonmagnetic dilution of magnetic Fe3+ (high spin) ions by Co3+ (low spin) ions due to B-site disorder essentially played a crucial role in manifesting such magnetic properties of the system.
38 citations
TL;DR: In this article, the authors reported the comprehensive experimental results identifying the magnetic spin ordering and the magnetization dynamics of a double perovskite Pr2CoFeO6 by employing the (dc and ac) magnetization, powder neutron diffraction (NPD) and X-ray magnetic circular dichroism (XMCD) techniques.
Abstract: We report the comprehensive experimental results identifying the magnetic spin ordering and the magnetization dynamics of a double perovskite Pr2CoFeO6 by employing the (dc and ac) magnetization, powder neutron diffraction (NPD) and X-ray magnetic circular dichroism (XMCD) techniques. X-ray diffraction and neutron diffraction studies revealed that Pr2CoFeO6 adopts a B-site disordered orthorhombic structure with space group Pnma. Additionally, ab initio band structure calculations performed on this system suggested an insulating anti-ferromagnetic (Fe-Fe) ground state. Magnetometry study showed the system to possess a spectrum of interesting magnetic phases including long range antiferromagnetic (canted) spin ordering (TN ~269 K), Griffiths phase, re-entrant cluster glass (RCG) (TG~ 34 K) and exchange bias. However, the NPD study divulged the exhibition of a long range G-type (below TN ~269 K) of spin ordering by Fe spins. Spin dynamics study by ac susceptibility technique confirmed the system possessing long range ordering at higher temperatureundergoes a RCG transition at ~34 K. Existence of Griffiths phase was confirmed by non-analytic field variation of magnetization and Heisenberg type temporal spin relaxation above long range ordering temperature TN ~269 K. The anti-site disorder related to the B-sites (Co/Fe) is found to be the main driving force forthe observed multiple magnetic phases. Furthermore, the electronic structure probed by the X-ray absorption spectroscopy (XAS) study suggested a nominal valance state of +3 for both of the B-site ions (Co/Fe) which in turn triggered the anti-site disorder in the system. Magnetic, XRD, NPD and XAS analysis yielded a low spin state (LS) for the Co3+ ions. The random non-magnetic dilution of magnetic Fe3+ (HS) ions by Co3+ (LS) ions essentially played a crucial role in manifesting the magnetic properties of the system.
30 citations
TL;DR: In this article, a detailed investigation of the crystal structure, magnetic, and magnetocaloric properties of the ordered monoclinic polycrystalline double perovskite Ho 2 CoMnO 6 (HCMO) compound was performed.
Abstract: The strong coupling between 3d and 4f based magnetic sublattices in double perovskite (DP) compounds results in various exotic complex magnetic interactions, and the ground state contains multiple fascinating and remarkable magnetic states. In this article, we have performed a detailed investigation of the crystal structure, magnetic, and magnetocaloric properties of the ordered monoclinic polycrystalline double perovskite Ho 2 CoMnO 6 (HCMO) compound. A study of the magnetization dynamics employing temperature and magnetic field shows a powerful correlation between Ho and Co/Mn sublattices. Due to the presence of the ferromagnetic superexchange interaction in between Co 2 + − O − Mn 4 + networks, the system undergoes an ordered state at the transition temperature, T C ≈ 77 K. Below T C, a clear compensation point continued by negative magnetization is noticed in the virgin state of the compound. The reduction of the saturation magnetization ( M S) in the hysteresis curves (M-H) can be explained by the existence of local anti-site defects or disorders and anti-phase boundaries in the system. Temperature dependence of magnetic entropy change ( − Δ S) curves shows a maximum value of 13.4 J/kg K for Δ H = 70 kOe at a low temperature along with a noticeable inverse magnetocaloric effect. Moreover, the material holds reasonable values of magnetocaloric parameters. The absence of thermal hysteresis along with a large value of | Δ S | makes the system a potential candidate for low temperature as well as liquid nitrogen temperature-based magnetic refrigeration. Additionally, our experimental findings should encourage further detailed studies on the complex 3d–4f exchange interaction in the double perovskite system.
27 citations
TL;DR: Some novel magnetic behaviours in double perovskite Eu2CoMnO6 (ECMO) have been reported and the AC susceptibility study demonstrates the Hopkinson like effect as well as the presence of volume spin-glass-like behaviour.
Abstract: Some novel magnetic behaviours in double perovskite Eu2CoMnO6 (ECMO) have been reported. The x-ray photoemission spectroscopy study shows the presence of mixed valence states of transition metal ions. The UV-visible absorption spectroscopic study suggests that the ECMO has a direct wide band gap. A second-order magnetic phase transition as a sudden jump in the magnetization curve has been observed around 124.5 K. The large bifurcation between the zero field cooling and field cooling, suggests existence of strong spin frustration in the system. The inverse DC susceptibility confirms the presence of the Griffiths like phase. Sharp steps in magnetization have been observed in the M-H curve at 2 K, which vanishes on increasing temperature. The AC susceptibility study demonstrates the Hopkinson like effect as well as the presence of volume spin-glass-like behaviour. The temperature dependent Raman spectrum shows the presence of spin-phonon coupling.
11 citations
TL;DR: It has been demonstrated that the observed MD at low and high temperatures are respectively due to the spin freezing and the spin-lattice coupling and the very large dielectric constant and the low loss suggest that La1.8Pr0.2CoFeO6 is very important from the application point of view.
Abstract: La based Co-Fe combined double perovskite (La1.8Pr0.2CoFeO6) was synthesized and the dielectric (zero-field and in-field), magnetic, x-ray absorption and Raman spectroscopy measurements have been investigated for La1.8Pr0.2CoFeO6 double perovskite. The existence of re-entrant cluster glass state is observed. The magneto-dielectric (MD) is found in two temperature regions (25-80 K and 125-275 K). It has been demonstrated that the observed MD at low and high temperatures are respectively due to the spin freezing and the spin-lattice coupling. Furthermore, the very large dielectric constant and the low loss suggest that La1.8Pr0.2CoFeO6 is very important from the application point of view.
7 citations
References
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TL;DR: VESTA has been upgraded to the latest version, VESTA 3, implementing new features including drawing the external morphology of crystals, and an extended bond-search algorithm to enable more sophisticated searches in complex molecules and cage-like structures.
Abstract: VESTA is a three-dimensional visualization system for crystallographic studies and electronic state calculations. It has been upgraded to the latest version, VESTA 3, implementing new features including drawing the external morphology of crystals; superimposing multiple structural models, volumetric data and crystal faces; calculation of electron and nuclear densities from structure parameters; calculation of Patterson functions from structure parameters or volumetric data; integration of electron and nuclear densities by Voronoi tessellation; visualization of isosurfaces with multiple levels; determination of the best plane for selected atoms; an extended bond-search algorithm to enable more sophisticated searches in complex molecules and cage-like structures; undo and redo in graphical user interface operations; and significant performance improvements in rendering isosurfaces and calculating slices.
15,053 citations
TL;DR: In this paper, a structure refinement method was described which does not use integrated neutron powder intensities, single or overlapping, but employs directly the profile intensities obtained from step-scanning measurements of the powder diagram.
Abstract: A structure refinement method is described which does not use integrated neutron powder intensities, single or overlapping, but employs directly the profile intensities obtained from step-scanning measurements of the powder diagram. Nuclear as well as magnetic structures can be refined, the latter only when their magnetic unit cell is equal to, or a multiple of, the nuclear cell. The least-squares refinement procedure allows, with a simple code, the introduction of linear or quadratic constraints between the parameters.
14,360 citations
TL;DR: Novel device paradigms based on magnetoelectric coupling are discussed, the key scientific challenges in the field are outlined, and high-quality thin-film multiferroics are reviewed.
Abstract: Multiferroic materials, which show simultaneous ferroelectric and magnetic ordering, exhibit unusual physical properties — and in turn promise new device applications — as a result of the coupling between their dual order parameters. We review recent progress in the growth, characterization and understanding of thin-film multiferroics. The availability of high-quality thin-film multiferroics makes it easier to tailor their properties through epitaxial strain, atomic-level engineering of chemistry and interfacial coupling, and is a prerequisite for their incorporation into practical devices. We discuss novel device paradigms based on magnetoelectric coupling, and outline the key scientific challenges in the field.
3,472 citations
TL;DR: In this article, the theory of double exchange was applied to perovskite-type manganites and detailed qualitative predictions about the magnetic lattice, the crystallographic lattice and the electrical resistivity were made.
Abstract: The theory of semicovalent exchange is reviewed and applied to the perovskite-type manganites $[\mathrm{La}, M(\mathrm{II})]\mathrm{Mn}{\mathrm{O}}_{3}$. With the hypothesis of covalent and semicovalent bonding between the oxygen and manganese ions plus the mechanism of double exchange, detailed qualitative predictions are made about the magnetic lattice, the crystallographic lattice, the electrical resistivity, and the Curie temperature as functions of the fraction of ${\mathrm{Mn}}^{4+}$ present. These predictions are found to be in accord with recent findings from neutron-diffraction and x-ray data as well as with the earlier experiments on this system by Jonker and van Santen.
3,148 citations
TL;DR: In this paper, an ordered double perovskite (Sr2FeMoO) was shown to exhibit intrinsic tunnelling-type magnetoresistance at room temperature.
Abstract: Colossal magnetoresistance—a huge decrease in resistance in response to a magnetic field—has recently been observed in manganese oxides with perovskite structure. This effect is attracting considerable interest from both fundamental and practical points of view1. In the context of using this effect in practical devices, a noteworthy feature of these materials is the high degree of spin polarization of the charge carriers, caused by the half-metallic nature of these materials20,21; this in principle allows spin-dependent carrier scattering processes, and hence the resistance, to be strongly influenced by low magnetic fields. This type of field control has been demonstrated for charge-carrier scattering at tunnelling junctions2,3 and at crystal-twin or ceramic grain boundaries4,5, although the operating temperature of such structures is still too low (⩽150 K) for most applications. Here we report a material—Sr2FeMoO6, an ordered double perovskite6—exhibiting intrinsic tunnelling-type magnetoresistance at room temperature. We explain the origin of this behaviour with electronic-structure calculations that indicate the material to be half-metallic. Our results show promise for the development of ordered perovskite magnetoresistive devices that are operable at room temperature.
2,065 citations