Showing papers on "Ferrimagnetism published in 1996"
TL;DR: The magnetization in the ferrimagnetic region below 16 kelvin was substantially increased after illumination and could be restored almost to its original level by thermal treatment and these effects are thought to be caused by an internal photochemical redox reaction.
Abstract: Photoinduced magnetization was observed in a Prussian blue analog, K0.2Co1.4- [Fe(CN)6]·6.9H2O. An increase in the critical temperature from 16 to 19 kelvin was observed as a result of red light illumination. Moreover, the magnetization in the ferrimagnetic region below 16 kelvin was substantially increased after illumination and could be restored almost to its original level by thermal treatment. These effects are thought to be caused by an internal photochemical redox reaction. Furthermore, blue light illumination could be used to partly remove the enhancement of the magnetization. Such control over magnetic properties by optical stimuli may have application in magneto-optical devices.
1,537 citations
TL;DR: In this paper, a molecular-based ferrimagnetic thin films with high critical temperatures (Tc) composed of mixed-valence chromium cyanides were synthesized by means of a simple electrochemical route.
Abstract: Molecular-based ferrimagnetic thin films with high critical temperatures (Tc) composed of mixed-valence chromium cyanides were synthesized by means of a simple electrochemical route. The highest Tc was 270 K, obtained for Cr2.12(CN)6. The Tc values were easily controlled by changing the preparation conditions. Moreover, a reversible shift of Tc could be electrochemically induced. As a result of such electrochemical control, these cyanides can be switched reversibly back and forth between ferrimagnetism and paramagnetism. These magnets thus represent materials in which magnetic properties are combined with electrical functions.
549 citations
TL;DR: All members of the M(II) = Mn series have magnetic susceptibilities showing broad maxima at 55 K characteristic of two-dimensional antiferromagnetism, but the magnetization of several of the salts increases sharply below 27 K due to the onset of spin canting.
Abstract: The synthesis and structural and magnetic characterization of 16 compounds AMIIFeIII(C2O4)3 (A = N(n-C3H7)4, N(n-C4H9)4, N(n-C5H11)4, P(n-C4H9)4, P(C6H5)4, N(n-C4H9)3(C6H5CH2), (C6H5)3PNP(C6H5)3, As(C6H5)4; MII = Mn, Fe) are reported. X-ray powder diffraction profiles are indexed in R3c or its subgroup P6522 or P6/mmm to derive unit cell constants. The structures of all the compounds consist of two-dimensional honeycomb networks [MIIFeIII(C2O4)3-]∞. The MII = Fe compounds behave as ferrimagnets with Tc between 33 and 48 K, but five exhibit a crossover from positive to negative magnetization near 30 K when cooled in a field of 10 mT. The compounds exhibiting this unusual magnetic behavior are those that have the highest Tc. Within the set N(n-CnH2n+1)4FeIIFeIII(C2O4)3 (n = 3−5), Tc increases with interlayer separation and the low-temperature magnetization changes from positive (n = 3) to negative (n = 4, 5). In the M = MnII compounds, the in-plane cell parameter a0 is ∼0.03 A greater than in the correspond...
494 citations
TL;DR: In this article, the role of superexchange interaction among 3D and 4d orbitals of transition metal ions via oxygen ions was investigated and the 1:1 ordered perovskite type compounds Sr2MMoO6 (M = Mn.Fe.Co) were prepared and their structures and properties were examined.
Abstract: In order to investigate the role of superexchange interaction among 3d and 4d orbitals of transition metal ions via oxygen ions. 1:1 ordered perovskite-type compounds Sr2MMoO6 (M = Mn.Fe.Co) were prepared and their structures and properties were examined. Structural analysis using the powder X-ray diffraction data revealed that all of these compounds have a 1:1 ordered arrangement in their B-sites. Measurements of electrical resistivity and magnetic susceptibility revealed that these compounds have the valency pairs of Mn2+ (3d5:t2g3eg2), Mo6+ (4d0). Fe3+ (3d5:t2g3eg2), Mo5+ (4d1:t2g1) and Co2+ (3d7:t2g5eg2), Mo6+ (4d0). The properties of these compounds are summarized as follows: Sr2MnMoO6, semiconductive and antiferromagnetic: Sr2FeMoO6, metallic and ferrimagnetic: Sr2CoMoO6, semiconductive and antiferromagnetic.
119 citations
TL;DR: In this paper, an integrated procedure for quantitative magnetic mineral extraction, based on the separation method of Petersen, von Dobeneck & Vali (1986), to examine the efficiency and representative nature of the extraction process was applied.
Abstract: We have applied an integrated procedure for quantitative magnetic mineral extraction, based on the separation method of Petersen, von Dobeneck & Vali (1986), to a range of sediment types, to examine the efficiency and representative nature of the extraction process. Carriers of magnetization have been identified by rock magnetic measurements, microscopy and X-ray diffraction. Quantification of the extraction efficiencies is achieved by before- and after-extraction rock magnetic measurements (susceptibility, anhysteretic and isothermal remanences). These magnetic measurements show that our modified extraction method extracts large proportions of the magnetization carriers in a range of sediment types (e.g. over 75 per cent for magnetite-dominated sediments). The extraction efficiency is dependent on the sample magnetic mineralogy and whether the magnetic grains occur as discrete grains or as inclusions within host grains. Susceptibility extraction efficiencies are strongly dependent on whether the susceptibility is of paramagnetic or ferrimagnetic origin. The amount of material recovered in the extract shows some inverse correlation with the density of the sediment suspension used during extraction. In terms of the mineralogies extracted, we identify a diverse and complex range of mineral assemblages. All sizes of discrete grains of magnetite are extracted (including single-domain and superparamagnetic grains, and chains of bacterial magnetite). Other commonly extracted iron and titanium oxides are haematite and ilmenite. Ferrimagnetic chromites and sulphides were also obtained from some samples. Considerable amounts of quartz and feldspar are extracted, due to the presence of magnetic inclusions within these diamagnetic host grains. In the deep-sea sediments we examined, feldspars constitute a large proportion of the extracts, but are significantly less abundant in other sediments, where quartz is dominant. A wide variety of paramagnetic minerals was identified in the extracts, including pyroxenes, amphiboles, chlorites, micas, Mg–Cr-spinels, garnets, Ti-oxides, apatites, tourmaline and zircon, many of which contain ferrimagnetic inclusions, possibly less than 0.1 μm in grain size. Dissolution of ultrafine grains of magnetite during pre-extraction carbonate dissolution, as suggested by Sun & Jackson (1994), does not occur in our samples.
108 citations
TL;DR: The crystal structure and magnetic properties of the molecular-based ferrimagnet N(n-C5H11)4MnIIFeIII(C2O4)3 have been determined as mentioned in this paper.
Abstract: The crystal structure and magnetic properties of the molecular-based ferrimagnet N(n-C5H11)4MnIIFeIII(C2O4)3 have been determined. The compound is orthorhombic, space group C2221, a= 9.707(3), b= 16.140(3), c= 19.883(7)A(120 K), Z= 4[R 0.047 for I > 2σ(I)]. The structure consists of hexagonal layers of alternating MnII and FeIII bridged by C2O42–, separated by layers containing only N(n-C5H11)4+ with the alkyl chains extended, though with the terminal bonds twisted towards the gauche conformation. The terminal CH3 are embedded in the hexagonal pockets formed by three C2O42–. Since both metal ions have 3d5 configuration with 6A1 ground states the magnetic properties in the paramagnetic region mimic those of a two-dimensional antiferromagnet. Below TN= 27 K an uncompensated moment estimated as 8.78 × 10–5µB atom–1 arises, the direction of which was identified as parallel to the c axis by single-crystal magnetization measurements.
104 citations
TL;DR: In this paper, the effect of magnetic annealing during the transition from the γMn phase to the D022-type phase and the addition of Fe to Mn3−δGa was studied.
Abstract: The D022‐type (Al3Ti‐type) phase in the Mn–Ga system is ferrimagnetic; the spin direction is parallel to the tetragonal c axis The Curie temperature is about 765 K (for δ=067), near the decomposition temperature We have prepared the D022‐type alloys by annealing the quenched ingots of the high‐temperature phase (γMn phase) at 400 or 300 °C for a long time The preparation becomes much easier if the ingots are powdered by filing before the annealing The single‐phase specimens of Mn3−δGa were obtained in the composition range 015≤δ≤106 The coercivity of some specimens was so large that we measured the magnetization curve in high magnetic fields up to 150 kOe The room‐temperature values of saturation magnetization, remanent magnetization, and coercivity of the powder sample of the alloy with δ=067 are 50 emu/g, 25 emu/g, and 135 kOe, respectively We have also studied the effect of magnetic annealing during the transition from the γMn phase to the D022‐type phase and the effect of the addition of Fe to Mn3−δGa of the D022‐type phase
102 citations
Abstract: The crystal structure of FeAlO3 has been determined at T = 298 K by neutron diffraction, using polycrystalline samples prepared in a high state of purity. The space group is Pna21, Z = 8; a = 4.9839 (1), b = 8.5544 (2), c = 9.2413 (2) A. The structure, which is isomorphous to that of FeGaO3, can be described as a double combination of hexagonal and cubic closed packing of oxygen ions. There are four different cation sites labelled Fe1, Fe2 (predominantly occupied by iron), Al1 and Al2 (predominantly occupied by aluminium). The oxygen environment of Al1 forms an almost regular tetrahedron. The other sites have a distorted octahedral environment, especially irregular for Fe1 and Fe2. The fractions fi of iron ions over the four cation sites are: f1 = 0.78 (1), f2 = 0.76 (1), f3 = 0.10 (1) and f4 = 0.34 (1). Neutron diffraction at T = 30 K reveals a classical Neel ferrimagnetism, the direction of easy magnetization being a, with strong `180° cation-anion-cation' super-exchange antiferromagnetic interactions Fe1—O—Fe2 and Fe1—O—Al2 (Al2 being a site occupied by 0.34 Fe). The Neel sublattices are A = Fe1 + Al1 and B = Fe2 + Al2. The average magnetic moment per atom is weak (3.4 ± 0.3 μB) and the spontaneous magnetization at T = 30 K is extremely weak: 0.38 ± 0.17 μB per atom. Piezoelectricity probably originates in the bond arrangement of the four tetrahedral All sites in the unit cell, each tetrahedron being oriented with an Al1—O bond parallel to the polar c axis.
75 citations
Patent•
24 Dec 1996TL;DR: In this article, the authors proposed a tunneling ferrimagnetic magnetoresistive sensor that can undergo a substantial change in resistance in response to a magnetic field in the intensity range of 10s of Oe, which is typical of the intensity of the magnetic fields encountered in magnetic recording media such as discs and tapes.
Abstract: A tunneling ferrimagnetic magnetoresistive sensor that has a ΔR/R greater than that of known magnetoresistive sensors, and that, with appropriate electrode materials, can undergo a substantial change in resistance in response to a magnetic field in the intensity range of 10s of Oe, which is typical of the intensity of the magnetic fields encountered in magnetic recording media such as discs and tapes. The tunneling ferrimagnetic magnetoresistive sensor is composed of a stack of thin-film layers that include a layer of a ferrimagnetic material, a layer of a magnetic material, and a layer of an insulator interposed between the layer of the ferrimagnetic material and the layer of the magnetic material. The ferrimagnetic material is conductive. The magnetic material is also conductive and has a coercivity substantially different from that of the ferrimagnetic material. The insulating layer is of a thickness that is sufficiently small to permit tunneling of current carriers between the layer of the ferrimagnetic material and the layer of the magnetic material.
55 citations
TL;DR: In this article, the authors investigated the magnetic properties of the rare earth compounds RMn2Ge2 (R = Tb, Ho, Er, Tm, Lu) by neutron diffraction.
52 citations
TL;DR: In this article, the Curie temperature of single-phase material is shown to be sensitive to the state of nonconvergent cation order, with a difference in Te of more than 70°C being observed between a sample quenched from 1400 °C and the same sample after heating to 650°C.
Abstract: Curie temperatures (Td of the (Fe304)x(MgA1204)1-xsolid solution have been determined from measurements of magnetic susceptibility (x) vs. temperature. The trend in Te vs. composition extrapolates to 0 K at x = 0.27. This behavior is rationalized in terms of the trend in cation distribution vs. composition suggested by Nell and Wood (1989), with Fe occurring predominantly on tetrahedral sites for x < 0.27. High-temperature x-T curves are nonreversible because of the processes of cation ordering and exsolution, which occur in the temperature range 400-650 0c. The Curie temperature of single-phase material is shown to be sensitive to the state of nonconvergent cation order, with a difference in Te of more than 70°C being observed between a sample quenched from 1400 °C and the same sample after heating to 650°C. This interaction between magnetic and chemical ordering leads to thermal hysteresis behavior such that Te measured during heating experiments is approximately 10°Chigherthan that measured during cooling. The hysteresis is due to a reversible difference in the state of cation order during heating and cooling caused by a kinetic lag in the cation-ordering behavior. Samples with compositions in the range 0.55 < x < 0.7 undergo exsolution to a mixture of ferrimagnetic and paramagnetic phases after heating to 650°C. Room-temperature hysteresis loops of the starting material and the high-temperature experiment products are compared. All starting materials are multidomain with coercivities He < 1.26 mT and Mr/ M, < 0.051. Samples that exsolved during the experiments have coercivities up to 20 mT and Mr/M, up to 0.36. This change in hysteresis properties is caused by grain subdivision during exsolution and implies a transition in the magnetic domain state from multito single-domain.
TL;DR: CoCu(pbaOH)3·2H2O (1) is a Co(II)Cu(II)-chain compound in which the ferrimagnetic chains interact antiferromagneticically within the lattice.
Abstract: CoCu(pbaOH)(H2O)3·2H2O (1) is a Co(II)Cu(II) chain compound in which the ferrimagnetic chains interact antiferromagnetically within the lattice. Removing the two noncoordinated water molecules through a thermal treatment results in the new chain compound CoCu(pbaOH)(H2O)3 (2) which exhibits a ferromagnetic ordering of the ferrimagnetic chains at Tc = 9.5 K. Removing a third water molecule, occupying the apical position in the copper coordination sphere, results in CoCu(pbaOH)(H2O)2 (3) which again exhibits a three-dimensional ferromagnetic ordering, but at Tc = 38 K. The field dependence of the magnetization for 3 reveals a coercive field of 5.66 × 103 Oe at 2 K, probably a record in the field of molecular-based magnets. This dehydration process giving rise to a crossover between long-range antiferro- and ferromagnetic states is reversible, and can be repeated.
TL;DR: In this paper, the magnetic properties of a decorated two-sublattice ferrimagnetic Ising model consisting of two magnetic atoms A and B with spins S A (S A = 1 2 ) and S B (S B > 1 2 ), were investigated within the framework of the effective field theory with correlations.
Abstract: The magnetic properties of a decorated two-sublattice ferrimagnetic Ising model consisting of two magnetic atoms A and B with spins S A (S A = 1 2 ) and S B (S B > 1 2 ) are investigated within the framework of the effective-field theory with correlations. The uniaxial crystal-field interaction D exists on the B atoms and the effects of SB and D on the magnetic properties are examined. We find a number of characteristic phenomena in these quantities, such as the possibility of two compensation points and the two (or three) transition temperatures, not predicted in the Neel theory.
TL;DR: The crystal and magnetic properties of the disordered spinel system CoFe2−xCrxO4 (x = 0.6) are investigated by means of X-ray, magnetization, Mossbauer effect and AC susceptibility measurements.
Abstract: The crystal and magnetic properties of the Cr-substituted disordered spinel system CoFe2−xCrxO4 (x = 0–1.6) are investigated by means of X-ray, magnetization, Mossbauer effect and AC susceptibility measurements. Variations of magnetic moment per formula unit measured at 80 K with Cr-content obtained from magnetization and Mossbauer data for x = 0–0.6 display a discrepancy between them, thus exhibiting a significant canting on the B-site which is satisfactorily explained on the basis of the non-collinear spin ordering model of random canting. Magnetization and Mossbauer results also show a sudden change near x > 0.6 indicating a change in magnetic structure from non-collinear to possibly collinear for x = 0.8–1.6. The AC susceptibility indicates a paramagnetic → unstable ferrimagnetic → cluster spin glass-type transition as the temperature is lowered for x = 0–1.2. The further increase in x from x > 1.2 increases frustration and disorder in the system supressing the ferrimagnetic ordering and the system approaches a cluster spin glass-type ordering at x = 1.4–1.6 as reflected in AC susceptibility and Mossbauer spectra.
TL;DR: In this paper, the magnetic properties of nanometer-scale particles are studied using the protein-complex ferritin as a vesicle for either an antiferromagnet or a ferrimagnet.
Abstract: The magnetic properties of nanometer‐scale particles are studied using the protein‐complex ferritin as a vesicle for either an antiferromagnet or a ferrimagnet. For antiferromagnetic ferritin particles, the anisotropy energy is found to depend linearly on the particle volume, suggesting that bulk anisotropy dominates over surface anisotropy. Effects due to the bulk and surface spins are discerned at high magnetic fields (27 T). At very low magnetic fields (1 nT) and temperatures (20 mK), the tunneling frequency of the Neel vector is observed to scale exponentially with the particle volume, consistent with the linear dependence of the anisotropy barrier on volume and with theories of macroscopic quantum coherence. In the ferrimagnetic particles, the anisotropy barrier decreases for smaller particles while simultaneously displaying a slight increase in coercivity and a dramatic decrease in the remanence over three orders of magnitude.
TL;DR: In this article, a disordered spinel series of CuFe 2-x Al x O 4 (x = 0.0−1.6) has been synthesized and studied by X-ray diffraction, magnetization, ac susceptibility and Mossbauer effect measurements.
TL;DR: In this article, the authors present direct current (dc) magnetization M(T,H) and alternating current (ac) susceptibility χac(t,H,f) data for the quasi-one-dimensional molecule-based ferrimagnet [MnTPP]::+[TCNE].
Abstract: We present direct current (dc) magnetization M(T,H) and alternating current (ac) susceptibility χac(T,H,f) data for the quasi‐one‐dimensional molecule‐based ferrimagnet [MnTPP]::+[TCNE].−⋅2PhMe (TPP=meso‐tetraphenylporphyrinato, TCNE=tetracyanoethylene). Static scaling of the real part χ′ of the ac susceptibility and data collapse of M(T,H) over a limited reduced temperature range above Tc≊13 K lead to the critical exponents γ≊1.6, β≊0.5, and δ≊4.2. Below Tc, χac depends sensitively on frequency and exhibits a striking double‐peak structure similar to that found in reentrant spin glasses. Possible models for the frequency dependence of the peaks observed in χac are discussed.
TL;DR: In this article, the interlayer magnetic exchange coupling between a spinglass material and a ferrimagnetic material was observed in NiFe2O4 bilayers, and the observed effect is reminiscent of the well-known exchange coupling effect between an antiferromagnetic magnet and a magnet magnet.
Abstract: Amorphous/crystalline bilayers of NiFe2O4 exhibit interlayer magnetic exchange coupling, which results from an interaction between a spin‐glass material and a ferrimagnetic material. The observed effect is reminiscent of the well‐known exchange coupling effect between an antiferromagnet and a ferromagnet, which is widely used in applications where field biasing of thin magnetic films is desirable.
TL;DR: In this paper, direct current magnetization studies are reported for the organic ferromagnet (NBu4)2Mn2[Cu(opba)]3 (TC=22 K), where opba stands for ophenylenebis (oxamato), and related compounds obtained by solvating it with dimethylsulphoxide, methanol, and acetonitrile, which have TC values of 15, 12, and 14.5 K.
Abstract: Direct current magnetization studies are reported for the organic ferromagnet (NBu4)2Mn2[Cu(opba)]3 (TC=22 K), where opba stands for o‐phenylenebis (oxamato), and related compounds obtained by solvating it with dimethylsulphoxide, methanol, and acetonitrile, which have TC values of 15, 12, and 14.5 K, respectively. M(H) plots for the first two compounds show very little width and criss‐cross at low applied field values (<50 Oe). Zero field‐cooled magnetization and field‐cooled magnetization curves for (NBu4)2Mn2[Cu(opba)]3 nearly overlap and its remanence plot changes sign at 11.5 K, exhibiting a compensation behavior. Negative remanent magnetization has also been observed for the other three compounds. The results are discussed in terms of the ferrimagnetic nature of the building blocks.
TL;DR: In this article, the magnetic susceptibility behavior of mixed-metal molecular-based compounds was investigated in the temperature range 5 −290 K. The compounds exhibit a crossover from ferromagnetic ordering for NBu 4 Fe(II)[Cr(III)(ox) 3 ] to ferrimagnetic ordering as a function of concentration.
TL;DR: In this paper, the magnetic properties of diluted mixed-spin Ising ferrimagnetic systems with coordination numbers z = 3 and 4 consisting of spin-1 2 and spin-3 2 have been investigated using the effective field theory with correlations.
TL;DR: In this paper, the magnetic interactions in the lattices of oxalate-bridged metal complexes {NBu4MFe(ox)3}x (M = Zn2+(1), Ni2+ (3)) have been investigated by using 57Fe Mossbauer spectroscopy.
TL;DR: In this article, the authors investigated the magnetic properties of a decorated Ising system consisting of three kinds of magnetic and non-magnetic atoms on the two-dimensional lattice, of which one with spin 1/2 forms a square lattice and the other two (a magnetic atom with a spin S (> 1/ 2) and a nonmagnetic atom) occupy randomly the middle points of each bond in the square-latice, under the framework of the effective field theory with correlations.
Abstract: The magnetic properties (transition temperature, compensation temperature and magnetization curve) of a decorated Ising system consisting of three kinds of magnetic and non-magnetic atom on the two-dimensional lattice, of which one with spin 1/2 forms a square lattice and the other two (a magnetic atom with a spin S (> 1/2) and a non-magnetic atom) occupy randomly the middle points of each bond in the square lattice, are investigated within the framework of the effective-field theory with correlations. Particular emphasis is given to the effects of S and crystal-field interaction D in the decorated magnetic atom on them. We find that the compensation temperature in the system may exhibit some interesting behaviours with the variation in S and D as well as the concentration p of the decorated spin-S atoms, such as the possibility of two compensation points induced by the variation in p.
TL;DR: In this paper, the possibility of a ferrimagnetic-in-plane configuration with C(2 × 2) symmetry was analyzed for V, Cr and Mn monolayers deposited on Fe(001).
TL;DR: In this paper, the first-principles electronic band structure calculations were performed for a cation-deficient NiAs-type ferrimagnet Fe7S8 (pyrrhotite) by using the linearized augmented-plane-wave (LAPW) method based on the local density approximation for the exchange-correlation potential.
TL;DR: In this paper, the magnetic properties of [1 0 0 0] oriented Fe3O4/NiO and Fe3 O4/CoO multilayers, MBE-grown on MgO(0 0 1) substrates, were studied by polarized neutron reflectometry.
Abstract: The magnetic properties of [1 0 0] oriented Fe3O4/NiO and Fe3O4/CoO multilayers, MBE-grown on MgO(0 0 1) substrates, have been studied by polarized neutron reflectometry. In both samples, the Fe3O4 layer exhibits a depth-dependent magnetic profile characterized by a reduction in the magnetization near the interfaces. The possible origins of this behaviour, such as domain wall formation in the ferrimagnetic layer and deviations in stoichiometry, are discussed.
TL;DR: In this article, the authors proposed a method for the fabrication of thin films of well-known ferrimagnetic materials such as NiFe2O4, CoFe 2O4 and BaFe12O19.
TL;DR: In this article, the specific heat has been measured for the ternary compounds, RMn2Ge2 (R = Gd. Tb and Dy), which show a ferrimagnetic to antiferromagnetic transition at low temperature.