Soft Ferrimagnet Research Articles

Comprehensive in-vitro and magnetic hyperthermia investigation of biocompatible non-stoichiometric Zn0.5Ca0.5Fe2O4 and Mg0.5Ca0.5Fe2O4 nanoferrites on lung cancer cell lines

In this research, the suitability and potential of two biocompatible mixed valent non-stoichiometric spinel nanoferrites viz., Zn0.5Ca0.5Fe2O4 (ZCNF) and Mg0.5Ca0.5Fe2O4 (MCNF) with a minor impurity of CaCO3 have been explored for magnetic hyperthermia and in-vitro cytotoxicity against normal and lung cancer cell lines. Nanocrystalline samples of ZCNF and MCNF in fcc structure were synthesized using the citrate-based sol-gel method and characterized by a variety of standard techniques. 57Fe Mössbauer spectroscopy, electron spin resonance and dc-magnetometry studies revealed that ZCNF is dominantly superparamagnetic while, MCNF is a soft ferrimagnet at 300 K. The maximum specific absorption rate (SAR) for 1 mg/mL suspension of nanoferrite powder in de-ionized water was found to be 179 W/g and 338 W/g for ZCNF and MCNF, respectively. Further, the highest hyperthermia temperature of 41.5 °C and 52 °C was achieved in 900 s at 15.98 kA/m for ZCNF and MCNF, respectively. Both ZCNF and MCNF showed good cytocompatibility with a tested concentration of 0.5 mg/mL against the human embryonic kidney HEK-293 (>75% cell viability) cell line. Additionally, simulated in-vitro treatment at an optimum magnetic hyperthermia temperature of 45 °C for 30 min in the presence of ZCNF and MCNF powder (up to a concentration of 1 mg/mL) led to suppression of ∼55% lung cancer cell lines (A549) while, in similar simulated condition the cell viability of normal HEK 293 cell lines remain unaffected. In summary, ZCNF and MCNF are appropriate therapeutic nanomaterials for magnetic hyperthermia-related cancer therapies.

Magnetic correlations in polycrystalline Tb0.15Co0.85

We investigated a polycrystalline sample of the ferrimagnetic compound Tb0.15Co0.85 by magnetometry and small-angle neutron scattering (SANS). The magnetization curve at 300 K is characteristic for soft ferrimagnets but at 5 K the hysteresis indicates the existence of magnetic domains. The magnetic SANS signal suggests that at 300 K the Tb and Co moments are correlated over large volumes within the micrometer-sized grains with correlation lengths >100 nm. At 5 K, however, the magnetic SANS analysis reveals a reduced correlation length of around 4.5 nm, which indicates the formation of narrow magnetic domains within the ferrimagnet with one dimension being in the nm range. We attribute the observed changes of the domain structure to the temperature-dependence of the magnetic properties of the Tb sublattice.

Magnetic ordering of Mo2NiB2-type {Gd, Tb, Dy)2Co2Al compounds by magnetization and neutron diffraction study

The magnetic ordering of Mo2NiB2-type {Gd, Tb, Dy}2Co2Al (Immm, No. 71, oI10) compounds has been established using bulk magnetic measurements and neutron diffraction study. Polycrystalline Gd2Co2Al, Tb2Co2Al and Dy2Co2Al undergo ferrimagnetic transitions (TC) at 78K, 98K and 58K, respectively, and low-temperature field induced transition (Tm) around 15K, 20K and 15K, respectively. Between Tm and TC Gd2Co2Al, Tb2Co2Al and Dy2Co2Al are soft ferrimagnets. Below Tm Gd2Co2Al is soft ferrimagnet, whereas Tb2Co2Al and Dy2Co2Al exhibit permanent magnet properties with residual magnetization per rare earth of 4.95B and 4.8B, respectively, and large coercive field of 72kOe and 22kOe, respectively, at 2K.The magnetocaloric effects of Gd2Co2Al, Tb2Co2Al and Dy2Co2Al were calculated in terms of isothermal magnetic entropy change and they reach maximum values of −10.4J/kgK, −7.6J/kgK and −6.6J/kgK for a field change of 50kOe near 75K, 98K and 58K, respectively. Low-temperature transition of Gd2Co2Al is followed by the magnetic entropy change of −2.9J/kg K in a field change of 50kOe at 15K. Low temperature magnetic ordering with enhanced anisotropic effects in Tb2Co2Al and Dy2Co2Al is accompanied by a positive magnetocaloric effect with isothermal magnetic entropy changes of +19.9J/kgK at 20K (field change 0–50kOe) and +2.7J/kgK at 15K (field change 0–10kOe), respectively.Neutron diffraction study shows that, in zero applied field, Tb2Co2Al exhibits c-axis ferrimagnetic ordering with magnetic space group Immm′ and propagation vector K0=[0, 0, 0] below TCND∼111K with MTb=8.86(15)B and MCo=0.26(2)B at 2K.

W3CoB3-type {Y, Gd - Ho}3Co4−xAlx (x=0.5−1) rare earth compounds: Specific features of crystal structure and magnetic ordering

The crystal structure of new W3CoB3-type {Y, Gd - Ho}3Co3.25Al0.75, Gd3Co3.5Al0.5 and Tb3Co3Al compounds (Cmcm. N 63, oC28) has been established using powder X-ray diffraction studies. The magnetic properties of Gd3Co3.5Al0.5, Gd3Co3.25Al0.75 and Tb3Co3.25Al0.75 were determined by bulk magnetization measurements and neutron diffraction studies. Gd3Co0.5Al0.5, Gd3Co3.25Al0.75 and Tb3Co3.25Al0.75 exhibit ferrimagnetic ordering below 196K, 161K and 151K, respectively. Tb3Co3.25Al0.75 shows a spin-reorientation transition at ~42K. Below the ferrimagnetic ordering temperature Gd3Co3.25Al0.75 and Tb3Co3.25Al0.75 are soft ferrimagnets, meanwhile Tb3Co3.25Al0.75 shows magnetic hardness below the spin-reorientation transition with remanent magnetization per formula unit of 9.7 μB and coercive field of 15kOe at 2K.The magnetocaloric effects of Gd3Co3.25Al0.75 and Tb3Co3.25Al0.75 were calculated in terms of isothermal magnetic entropy change and they reach maximum values of −4.9J/kg·K at 135–145K and −3.7J/kg·K at 115–135K, respectively, for a field change of 0–50kOe. Low temperature magnetic ordering in Tb3Co3.25Al0.75 is accompanied by a positive magnetocaloric effect with isothermal magnetic entropy changes of +13.6J/kg·K at 10K for a field change of 0–50kOe and +0.9J/kgK at 45K for a field change of 0–10kOe.Neutron diffraction study in zero applied field shows mixed ferro-antiferromagnetic ordering of Tb3Co3.25Al0.75 with a wave vector K0=[0, 0, 0]. Below ~ 137K Tb3Co3.25Al0.75 exhibits non-collinear ferrimagnetic ordering of terbium and cobalt sublattices with resulting of b-axis ferromagnetic and c-axis antiferromagnetic components of Cmc′m={1, mx}×{1, mz/[0, 0, 1/2]}×{1, i′}×{1, 1/[1/2, 1/2, 0]} magnetic space group. The spin-reorientation transition in Tb3Co3.25Al0.75 below ~38K corresponds to appearance of additional a-axis ferromagnetic component and decreasing of symmetry of magnetic ordering down to C2′/c={1, mz/[0, 0, 1/2]}×{1, i′}×{1, 1/[1/2, 1/2, 0]} magnetic space group.

Microwave absorption properties of (100−x)La1.5Sr0.5NiO4/xNiFe2O4 nanocomposites

A combination of dielectric and magnetic materials is expected to demonstrate strong capability of absorbing microwave radiation. In this work, nanocomposite samples made of La1.5Sr0.5NiO4 (LSNO), which has a large dielectric constant, and NiFe2O4 (NFO), which is a typical soft ferrimagnet with high permeability, are prepared and used for measurements in the radar range of 4–18 GHz. The radar absorption capability is characterized by the reflection loss (RL) based on the method proposed by Nicolson – Ross – Weir (hence called NRW method) and the transmission line theory. Lowest RL values of −29.7 dB and −28.5 dB are found for the NFO concentration x = 8 and 30, respectively. Importantly, we observed that the absorption peak shifts to higher frequencies with higher NFO contents, likely due to either the ferromagnetic resonance mechanism or a direct result of the dielectric-magnetic balancing. By attaching a metal (Al) plate to the back of the samples, we are able to observe the phase matching resonance where the reflection signal S11 is almost vanished in the low frequency regime.

A Monte Carlo study of the magnetization reversal in DyFe2/YFe2 exchange-coupled superlattices

Monte Carlo simulations are used to perform an atomic scale modeling of the magnetic properties of epitaxial exchange-coupled DyFe2/YFe2 superlattices. These samples, extremely well-researched experimentally, are constituted by a hard ferrimagnet DyFe2 and a soft ferrimagnet YFe2 antiferromagnetically coupled. Depending on the layers’ thickness and on the temperature, the field dependence of the magnetization depth profile is complex going from a unique giant ferromagnetic block to exchange spring behavior when the soft YFe2 layers reverse for positive bias fields. In some particular conditions of temperature and layers׳ thicknesses, it can even be easier to reverse the hard thin DyFe2 layers for positive fields, while the soft thick YFe2 layers keep their magnetization along the field. In this work, we reproduce by Monte Carlo simulations hysteresis loops for the net and compound-specific magnetizations at different temperatures, and assess the quality of the results by a direct comparison to experimental hysteresis loops.

Room temperature and near-room temperature coordination polymer magnets

Four new vanadium-based coordination polymers that exhibit high magnetic ordering temperatures (Tc) have been synthesized. Magnetic measurements show that these polymers are soft ferrimagnets. The IR shows a reduced nitrile environment in these polymers, elemental analysis reveals that the compositions of the polymers are 2:1 acceptor to vanadium ratio. An electrochemical measurement of acceptors shows a weak correlation between Tc and the redox potentials. Change in the dihedral angle of an acceptor with the substitution in a specific position of the phenyl ring alters the magnetic ordering temperature in these polymers. Calculated electron affinity and Mullikan spin densities on acceptors, either in the neutral or in the anionic form, shows no relationship with the observed trend in Tc. These compounds are analogues to V[TCNE]2 complexes with varying degree of solvent of coordination.

Half-metallicity in the ferrimagnet [MnII(enH)(H2O)][CrIII(CN)6]·H2O: Ab initio study

The density-functional theory (DFT) within the full potential linearized augmented plane wave (FPLAPW) method is applied to study the two-dimensional achiral soft ferrimagnet [MnII(enH)(H2O)][CrIII(CN)6]·H2O. The phase stability, electronic structure, magnetic and conducting properties are investigated. Our results reveal that the compound has a stable ferrimagnetic ground state in good agreement with the experiment. From the spin density distribution, the spin magnetic moment of the compound is mainly from Cr3+ and Mn2+ ions with small contributions from the oxygen, nitrogen and carbon ions. The calculated electronic band structure predicts the compound to be a half-metal with the spin magnetic moment of 1.000μB per molecule.

Magnetocaloric Effect in a Mn2‐Pyridazine‐[Nb(CN)8] Molecular Magnetic Sponge

AbstractA comprehensive study of the magnetocaloric effect (MCE) in the Mn2‐[Nb(CN)8] molecular magnet with a two‐step magnetic sponge behavior is reported. The structural transformations provoked by dehydration bring about an increase in the magnetic ordering temperature (Tc) from 43 K through to 68 K and up to 98 K. All three phases are soft isotropic ferrimagnets. The change in magnetic entropy in the partially and fully dehydrated phases is smaller than that in the “as synthesized” form by a factor of 0.6. The field dependence of MCE at Tc is consistent with the values of the critical exponents derived from the magnetization data.

Perpendicular exchange bias in ferrimagnetic spin valves

The exchange bias effect refers to the shift of the hysteresis loop of a ferromagnet in direct contact to an antiferromagnet. For applications in spintronics a robust and tunable exchange bias is required. Here we show experimental evidence for a perpendicular exchange bias in a prototypical ferrimagnetic spin valve consisting of DyCo(5)/Ta/Fe(76)Gd(24), where the DyCo(5) alloy has the role of a hard ferrimagnet and Fe(76)Gd(24) is a soft ferrimagnet. Taking advantage of the tunability of the exchange coupling between the ferrimagnetic layers by means of thickness variation of an interlayer spacer, we demonstrate that perpendicular unidirectional anisotropy can be induced with desirable absolute values at room temperature, without making use of a field-cooling procedure. Moreover, the shift of the hysteresis loop can be reversed with relatively low magnetic fields of several hundred Oersteds. This flexibility in controlling a robust perpendicular exchange bias at room temperature may be of crucial importance for applications.

Magnetic properties of Exchange-spring DyFe2/YFe2 Superlattices by Monte Carlo Simulations

ABSTRACTMonte Carlo simulations are used to perform an atomic scale modelling of the magnetic properties of epitaxial exchange-coupled DyFe2/YFe2 superlattices. These samples, extremely well-researched experimentally, are constituted by a hard ferrimagnet DyFe2 and a soft ferrimagnet YFe2 antiferromagnetically coupled. Depending on the layers and on the temperature, the field dependence of the magnetization depth profile is complex. In this work, we reproduce by Monte Carlo simulations hysteresis loops for the net and compound-specific magnetizations at different temperatures, and assess the quality of the results by a direct comparison to experimental hysteresis loops.

Structure and magnetic properties of ionic compound (Cp*2Cr+)·(FeIPc−)·(C6H4Cl2)4containing negatively charged iron phthalocyanine

A new strategy for the preparation of molecular magnets by the reduction of phthalocyanines with strong metallocene donors has been suggested. Compound (Cp*2Cr+)·(FeIPc−)·(C6H4Cl2)4 (1) contains uniform stacks of alternating closely packed Cp*2Cr+ and FeIPc− ions. 1 is a soft ferrimagnet showing hysteresis with a small coercive field and a bifurcation temperature of about 5 K.

Substituting group induced structural transformation from 1D zigzag chain to 2D grid network in cyano-bridged dimetallic complexes derived from Mn III(Schiff-base) and [Cr I(CN) 5NO] 3−: Synthesis, crystal structure and magnetic properties

Two cyano-bridged dimetallic complexes derived from Mn III(Schiff-base) and [Cr I(CN) 5NO] 3−, [Mn(3-CH 3)salen] 3[Cr(CN) 5NO]·2.5H 2O ( 1) and [Mn(5-CH 3)salen] 6[Cr(CN) 5NO] 2·2CH 3OH·16H 2O ( 2) [salen = N,N′-ethylenebis (salicylideneiminato)dianion] were synthesized and characterized. The reaction conditions of the two complexes are identical. The substituting group (CH 3–) in the salen-type ligands gives different assembly styles for the two complexes, 1D zigzag chain for 1 while 2D grid network for 2. The magnetic investigation indicates the dominant antiferromagnetic interactions between the Mn(III) and Cr(I) mediated by the CN bridge. Due to the weak interchain antiferromagnetic interactions, no magnetic ordering phase was observed in complex 1. Interestingly, complex 2 showed the long range ferrimagnetic magnetic ordering with T c = 9 K, in contrast to 1. Furthermore, the hysteresis loop confirms the nature of complex 2 as soft ferrimagnet.

Monte Carlo simulation of the magnetic exchange spring system DyFe2(1) /YFe2(4)

We investigate the magnetic properties of exchange coupled super-lattices constituted by a hard ferrimagnet DyFe2 and a soft ferrimagnet YFe2. The interface is characterized by a strong antiferrromagnet due to the negative exchange couplings between the Dy and Fe magnetic moments. In this work, we reproduce hysteresis loops for the net and compound-specific magnetisations at different temperatures, by means of Monte Carlo simulations, and assess the quality of our results by a direct comparison to experimental hysteresis loops.

Multifunctional Magnetic Molecular {[MnII(urea)2(H2O)]2[NbIV(CN)8]}n System: Magnetization-Induced SHG in the Chiral Polymorph

Incorporation of urea molecules into the magnetic system MnII-[NbIV(CN)8] results in formation of two magnetic polymorphs {[MnII(H2O)(urea)2]2[NbIV(CN)8]}n chiral α and centric β crystallizing in space groups P41 and P1̅, respectively. Both polymorphs exhibit extremely similar structures and are soft ferrimagnets with critical temperatures of 43 and 42 K, respectively. The presence of coordinated urea in the noncentrosymmetric α produces NLO functionality, second harmonic generation (SHG), whereas centric β is just another molecular magnet. As a result of interaction of both functionalities below magnetic ordering temperature, the magnetization-induced SHG (MSHG) is observed for polymorph α. The observed MSHG/SHG signal ratio was the largest among molecule-based noncentrosymmetric magnets. The presence of urea molecules in both polymorphs gives also rise to their interesting topotactic reactivity. Both polymorphs can be easily transformed into a new entity {[MnII(H2O)]2[NbIV(CN)8]·2.5MeOH}n 2b with significant shift of critical temperature Tc to 70 K. Subsequent hydration of 2b leads to {[MnII(H2O)2]2[NbIV(CN)8]·4H2O}n 3 with Tc of 47 K.

Substrate-modified ferrimagnetism in MnGa films

We report the substrate-modified magnetic properties of the CuAu type-I (L10) structure of MnxGa (1.2<x<1.5) films. The magnetic properties of the MnGa films differed greatly due to the influence of the substrate. The MnGa film is a hard ferrimagnet when grown on GaSb (111), becomes a soft ferrimagnet when grown on Al2O3 (0001), and exhibits an absence of a net magnetic moment when stabilized on a GaSb (100) substrate. This difference was attributed to the substrate, which forces MnGa film to be two-dimensionally stabilized in a different orientation and thus leads to the modified crystal symmetry and a change in the magnetic property. The results may be helpful for forming a comprehensive understanding of MnGa and for finding new applications in spintronic devices.

Consecutive Irreversible Single-Crystal to Single-Crystal and Reversible Single-Crystal to Glass Transformations and Associated Magnetism of the Coordination Polymer, [MnII(rac-pnH)(H2O)CrIII(CN)6]·H2O

The achiral coordination polymer [Mn(II)(rac-pnH)(H(2)O)Cr(III)(CN)(6)].H(2)O, (rac-pn = racemic 1,2-diaminopropane), 1.2H(2)O, has been prepared, and its crystal structures, optical and magnetic properties have been studied before and after dehydration followed by rehydration. The in situ X-ray diffraction, performed on one selected single crystal, shows an unusual irreversibility from the as-prepared 1.2H(2)O to the dehydrated [Mn(rac-pnH)Cr(CN)(6)], 1, and reversibility from 1 to rehydrated [Mn(rac-pnH)(H(2)O)Cr(CN)(6)].H(2)O 1-HP. Virgin 1.2H(2)O crystallizes in the monoclinic achiral P2(1)/m space-group having a two-dimensional (2D) square-network of Mn-Cr with bridging cyanide, and behaves as a soft ferrimagnet (T(C) = 36 K). Dehydrated 1 has a three-dimensional (3D) network with an additional cyanide bridge between layers and adopts the orthorhombic achiral Pmnb space-group exhibiting a ferrimagnetic behavior (T(C) = 70 K). Rehydrated 1-HP (T(C) = 36 K) is poorly crystallized having the same unit-cell as 1.2H(2)O and reversibly transforms to the crystalline 1 (T(C) = 70 K). The dehydration is associated to a change in the coordination of the amine from one layer to its neighboring one involving a proton transfer, going from {Mn-NH(2)CH(CH(3))CH(2)N'H(3)(+).....(H(2)O)Mn'} for 1.2H(2)O to {Mn-NC.....NH(3)(+)CH(CH(3))CH(2)H(2)N'-Mn'} for 1. The irreversible transformation of virgin single crystal 1.2H(2)O to single-crystal 1 is promoted by the availability of only one Mn in the vicinity of the cyanide while during the rehydration process the reversible single-crystal 1 to a glassy 1-HP is due to the presence of two equidistant Mn atoms, which is the cause of the disorder. The change in magnetism, that is, the increase of the Curie temperature and coercive field, is associated to the structural transformation from 2D to 3D.

On the Nature of the Reversibility of Hydration—Dehydration on the Crystal Structure and Magnetism of the Ferrimagnet [MnII(enH)(H2O)][CrIII(CN)6]·H2O

We report the synthesis, crystal structure, and thermal and magnetic properties of the two-dimensional achiral soft ferrimagnet [Mn(II)(enH)(H(2)O)][Cr(III)(CN)(6)].H(2)O (1), en = 1,2-diaminoethane, as well as the recyclability of the dehydration and rehydration and their influence on the crystal structure and its magnetic properties. Unlike [Mn(S-pnH)(H(2)O)][Cr(CN)(6)].H(2)O (2S, pn = 1,2-diaminopropane), which is a chiral (P2(1)2(1)2(1)) enantiopure ferrimagnet (T(C) = 38 K), 1 crystallizes in the achiral orthorhombic Pcmn space group, having a similar two-dimensional square network of Mn-Cr with bridging cyanide, and 1 behaves also as a soft ferrimagnet (T(C) = 42 K). X-ray diffraction experiments on a single crystal of 1 indicate a transformation from a single crystal to an amorphous phase upon dehydrataion and partial recovery of its crystallinity upon rehydration. The dehydrated phase 1-DP exhibits long-range ordering at 75 K to a ferrimagnetic state and coercive field at 2 K of 100 Oe, which are a higher critical temperature and coercive field than for the virgin sample (H(C) = 60 Oe). Thermogravimetric analyses indicate that the crystallinity deteriorates upon hydration-dehydration cycling, with persistence toward the amorphous phase, as also seen by magnetization measurements. This effect is associated with an increase of statistical disorder inherent in the dehydration-rehydration process. X-ray powder diffraction suggests that 1-DP may retain order within the layers but loses coherence in the stacking of the layers.

Reversible Single Crystal-to-Amorphous Phase Transition upon Dehydration–Rehydration and Associated Magnetism in [MnII(enH)(H2O)][CrIII(CN)6]·H2O

Abstract We report the rare occurrence of a reversible loss of crystallinity upon dehydration and regain upon rehydration by in situ X-ray diffraction on a single crystal of [MnII(enH)(H2O)][CrIII(CN)6]·H2O and the associated thermal and magnetic properties characterized by an increase of the Curie temperature of the soft ferrimagnet from 42 to 75 K.

A room temperature ferrimagnet, vanadium[pentafluorophenyltricyanoethylene] 2

The emergence of the soft ferrimagnet V[TCNE] 2 has sparked interest in the development of new radical anionic bridged magnets that are ordered above room temperature. Reversible one-electron acceptors 2-(phenyl)-1,1,2-tricyanoethylene, H 5PTCE, and 2-(pentafluorophenyl)-1,1,2-tricyanoethylene, F 5PTCE, are replacements for TCNE, giving magnets in reactions with V(CO) 6 that order at 215 K and 307 K, respectively. Both compounds exhibit hysteresis with small coercivities at 5 K which is typical of this class of compounds.