Nonmagnetic Ions Research Articles

Impurity-Induced Antiferromagnetism in S = 1/2 Alternating Chain System NaCu2VP2O10

Impurity-induced antiferromagnetism was observed in the S = 1/2 alternating chain compound NaCu2VP2O10 when a few nonmagnetic ions were substituted at the Cu sites. NaCu2VP2O10 showed a nonmagnetic spin-singlet ground state at low temperatures. The temperature dependence of the magnetic susceptibility and the specific heat of the Mg-doped compounds, Na(Cu1−xMgx)2VP2O10 \((x = 0.03,0.05)\), showed anomalies at ∼8 K, indicating antiferromagnetic ordering.

Prediction of half-metallic ferrimagnetic quadruple perovskites ACu3Fe2Re2O12 (A=Ca, Sr, Ba, Pb, Sc, Y, La) with high Curie temperatures

A- and B-site ordered quadruple perovskites with the chemical formula ${\mathrm{AA}}_{3}^{\ensuremath{'}}{\mathrm{B}}_{2}{\mathrm{B}}_{2}^{\ensuremath{'}}{\mathrm{O}}_{12}$ can form with 1:3 ratio at the A site. A unique feature of this specially ordered perovskite is that three different atomic sites $({\mathrm{A}}^{\ensuremath{'}}, \mathrm{B}, \mathrm{and} {\mathrm{B}}^{\ensuremath{'}}$ sites) can all accommodate magnetic transition metals. As a consequence, multiple magnetic and electronic interactions can occur at ${\mathrm{A}}^{\ensuremath{'}}$, B, and/or ${\mathrm{B}}^{\ensuremath{'}}$ sites, giving rise to a series of intriguing physical phenomena. ${\mathrm{CaCu}}_{3}{\mathrm{Fe}}_{2}{\mathrm{Re}}_{2}{\mathrm{O}}_{12}$ is a good example, which shows half-metallic electronic structure, large magnetization, and a very high Curie temperature. Here we investigated a series of ferrimagnetic (FiM) compounds ${\mathrm{ACu}}_{3}{\mathrm{Fe}}_{2}{\mathrm{Re}}_{2}{\mathrm{O}}_{12}$ (A=Ca, Sr, Ba, Pb, Sc, Y, La) by using density functional theory and Monte Carlo simulations. We found that all compounds with ${\mathrm{A}}^{2+}$ ions exhibit high Curie temperatures (above 405 K), and the compounds with ${\mathrm{A}}^{3+}$ substitution yield even higher ${T}_{C}$ (above 502 K). By examining interatomic exchange parameters, we found that the antiferromagnetic exchange couplings between Re and Cu as well as Re and Fe are responsible for this very high Curie temperature. For the compounds with ${\mathrm{A}}^{3+}$ substitution, electron doping in bands around the Fermi level dominated by the Re ions strengthens the Re-Cu, Re-Fe, and Re-Re exchange interactions, which cause an increase in the critical temperature. Finally, we calculated the formation energies of the quadruple perovskites with respect to the possible decomposition pathways and have found that the values are reasonable for the synthesis of these compounds under the conditions of high pressure and high temperature. In summary, this work demonstrates a design strategy of enhancing the spin ordering temperature by replacing A-site nonmagnetic ions.

Mossbauer studies of Zn-substituted BiFeO3 multiferroic

This work presents an elaborate study of the effect in the structural and magnetic of [Formula: see text] ([Formula: see text], 0.05, 0.10, 0.15, 0.20, 0.25) multiferroic materials, synthesized via a sol-gel auto-combustion method. The synthesized materials are found to have structural distortion in the rhombohedral R3c structure as observed by X-ray diffraction (XRD). Other diffraction peaks were attributed to the second phase [Formula: see text]. The Mossbauer spectra (MS) of [Formula: see text] ([Formula: see text], 0.05, 0.10, 0.15) are fitted with a sextet and a doublet, and the presence of doublet also indicates the [Formula: see text] phase. The results from XRD and MS both show that Zn-substituted BiFeO3 suffers adverse effects on the formation of pure BiFeO3. [Formula: see text] ([Formula: see text], 0.25) are fitted with only one paramagnetic doublet. The absence of sextet means that there is a magnetic destruction of samples on account of a thorough phase transition from a magnetic phase to a non-magnetic phase and/or successful ion substitution (iron ions were replaced with zinc ions).

Room-Temperature Magnetoelectric Coupling in Electronic Ferroelectric Film based on [(n-C3H7)4N][FeIIIFeII(dto)3] (dto = C2O2S2).

Great importance has been attached to magnetoelectric coupling in multiferroic thin films owing to their extremely practical use in a new generation of devices. Here, a film of [(n-C3H7)4N][FeIIIFeII(dto)3] (1; dto = C2O2S2) was fabricated using a simple stamping process. As was revealed by our experimental results, in-plane ferroelectricity over a wide temperature range from 50 to 300 K was induced by electron hopping between FeII and FeIII sites. This mechanism was further confirmed by the ferroelectric observation of the compound [(n-C3H7)4N][FeIIIZnII(dto)3] (2; dto = C2O2S2), in which FeII ions were replaced by nonmagnetic metal ZnII ions, resulting in no obvious ferroelectric polarization. However, both ferroelectricity and magnetism are related to the magnetic Fe ions, implying a strong magnetoelectric coupling in 1. Through piezoresponse force microscopy (PFM), the observation of magnetoelectric coupling was achieved by manipulating ferroelectric domains under an in-plane magnetic field. The present work not only provides new insight into the design of molecular-based electronic ferroelectric/magnetoelectric materials but also paves the way for practical applications in a new generation of electronic devices.

Non-magnetic ions doping effects in the magnetic properties of zircon-type GdCrO4 compound

In this paper, we report the effect of V and Y-doping on the structural and magnetic properties of the GdCrO4 compound obtained by the co-precipitation method. The analysis of the X-ray diffraction data using the Rietveld refinement confirm the formation of a single phase consistent with the zircon-type structure (tetragonal and I41/amd space group) and a decreasing of lattice parameter with increasing of doping. The T-dependent magnetic susceptibility is consistent with a ferromagnetic and an antiferromagnetic orders for YCrO4 and GdVO4 samples, respectively. On the other hand, the positive signal of Curie–Weiss constants of doped samples indicate the predominance of ferromagnetic correlations. Furthermore, the displacement of the maximum of susceptibility and the thermal hysteresis as a function of doping can be an indication of frustration effects. Isothermal magnetization measured at T = 2 K show a change of slope at low magnetic fields for V-doped samples and a decrease of the magnetic moment for Y-doped GdCrO4. At T = 15 K, the analysis of MvsH curves reveal that only part of Gd3+ magnetic moments are ordered.

Effect of nonmagnetic substituent Zn on the phase competition and multiferroic properties in the polar magnet Fe2Mo3O8

The polar magnet, Fe2Mo3O8 (FMO), with linear magnetoelectric (ME) coupling, is a promising candidate for multiferroic applications in advanced spin devices. However, a giant magnetic bias (Hb) is needed for optimizing the inverse ME effect, i.e., electric field (E) modulation of magnetization (M), which is still a core issue. Herein, we utilize the chemical doping route to enhance the sensitivity of controlling the competitive magnetic interactions and/or multiferroic phases by means of introducing nonmagnetic Zn2+ ions into FMO crystals. Compared with FMO, the Zn-doped composition (Fe0.95Zn0.05)2Mo3O8 (FZMO) generates three metastable magnetic states in the middle of antiferromagnetic and ferrimagnetic states, along with obvious ferroelectric polarization. The inverse ME effect of FZMO is intact with a relative change of ΔM ≈ 0.06 μB/f.u. responding to an E value of ± 20 kV/cm at 52 K. Most interestingly, the exciting Hb is dramatically dropped to 0.8 T for FZMO from 5.1 T for FMO, which is in favor of the application of ME coupling. It is suggested that the perturbation of magnetic interactions via substituting specific sites by nonmagnetic ions plays a key role in decreasing the exciting Hb without deteriorating the inverse ME coupling in this polar M2Mo3O8 family.

Spin dynamics in the alternating chain system Li3Cu2SbO6 with defects probed by nuclear magnetic resonance

We report the results of the detailed measurements of $^{7}\mathrm{Li}$ nuclear magnetic resonance (NMR) spectra, NMR line shift, spin-lattice relaxation rate, bulk magnetization, magnetic susceptibility, and heat capacity on the spin-$\frac{1}{2}$ Heisenberg honeycomb compound ${\mathrm{Li}}_{3}{\mathrm{Cu}}_{2}{\mathrm{SbO}}_{6}$. This system consists of weakly coupled alternating Cu chains and, owing to the site inversion, some of the magnetic Cu ions are substituted by nonmagnetic Li ions. As a result, the effective spin model for ${\mathrm{Li}}_{3}{\mathrm{Cu}}_{2}{\mathrm{SbO}}_{6}$ is a set of Cu alternating chain fragments of different length (the ``chain-segments spin model''). Due to this unique structure, various kinds of peculiar magnetic features arise and the combination of local (NMR) and global experimental techniques is especially effective in their study. In order to describe the experimental results theoretically, we perform full diagonalization calculations for the chain-segments spin model taking explicit account of all of the possible dimerized chain fragments of different length. From the fitting of measured susceptibility, we estimate the exchange interactions as ${J}_{\mathrm{FM}}=\ensuremath{-}244\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${J}_{\mathrm{AF}}=146\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, and find that about 19% of magnetic Cu ions are replaced by nonmagnetic Li ions. Using those values, we can even quantitatively reproduce the observed NMR line shift and the specific heat as well as field- and temperature-dependent magnetization over a wide temperature range. Although small deviations are seen at very low temperature, they can be corrected by considering the effect of small interchain interactions.

Enhanced room‐temperature magnetoelectric coupling effects in c‐axis oriented polycrystalline BaSrCo2‐xMgxFe11AlO22

AbstractThe influence of applied magnetic field during annealing process as well as of Mg doping on the room‐temperature magnetoelectric coupling effects in BaSrCo2‐xMgxFe11AlO22 are experimentally studied through the magnetization, magnetodielectric, and magnetoelectric current measurements. Hexaferrite samples of Co2Y were found to be highly oriented by an applied magnetic field (Ho) during the annealing process, leading to an enhancement of the room‐temperature magnetoelectric coupling effects. Although the substitution of nonmagnetic Mg ions in Co sites tends to reduce the ferromagnetism at macroscopic scale, a proper amount of Mg doping content facilitates the superexchange interaction between the adjacent magnetic blocks; meanwhile modulates the magnetic anisotropy in the samples. An appropriate adjustment of the competition between the anisotropy and the superexchange could enhance the magnetoelectric coupling at room temperature, which can be confirmed by the magnetic‐field‐induced dielectric constant and current density study.

Magnetic properties of Ni5Sn(O2BO3)2 ludwigite

The magnetic properties of site-disordered ${\mathrm{Ni}}_{5}\mathrm{Sn}{({\mathrm{O}}_{2}{\mathrm{BO}}_{3})}_{2}$ ludwigite have carefully been studied using local probes and bulk experimental methods in temperatures down to 1.6 K and magnetic fields up to 9 T. Our results have clearly shown the role of the effect of order/disorder site occupancy in these complex compounds with spin moments $S=1$. Different from most ludwigites, site-disordered ${\mathrm{Ni}}_{5}\mathrm{Sn}{({\mathrm{O}}_{2}{\mathrm{BO}}_{3})}_{2}$ ludwigite has shown three magnetic transitions at 80, 50, and 5 K. Local probes ($^{119}\mathrm{Sn}$ M\"ossbauer and muon spin spectroscopy) have indicated a partial long-range magnetic order with onsets at 80 and 50 K with predominant ferromagnetic interactions at 80 K and antiferromagnetic ones at 50 K. At lower temperatures, a partial spin-glass-like freezing of the moments has been developed concomitantly with fraction of the moments ordered at higher temperatures, a spin-glass-like and long-range magnetic order coexist and a spontaneous exchange bias effect has been observed. Applied magnetic fields have gradually reduced magnetic frustration, leading to a magnetically ordered state of the complete structure at 51 K under 9 T. The absence of double-exchange interactions in order/disorder ${\mathrm{Ni}}_{5}\mathrm{Sn}{({\mathrm{O}}_{2}{\mathrm{BO}}_{3})}_{2}$ ludwigites shows how the magnetic interactions that compete as direct exchange and double exchange are modified by the site occupancy of nonmagnetic Sn ions. Features as a third magnetic transition, the appearance of spontaneous exchange bias, and the enhancement of the coercive field at low temperatures were not found in the site-ordered isomer compound.

Magnetization and thickness dependent microwave attenuation behaviour of Ferrite-PANI composites and embedded composite-fabrics prepared by in situ polymerization

Ultrahigh efficient and effective electromagnetic-interference (EMI) shielding composites have been fabricated with the combination of Polyaniline and zinc-cobalt ferrites (Co1-xZnxFe2O4, 0.1 ≤ x ≤ 0.4). Ferrite nanoparticles synthesized via the sol-gel method were functionalized to polyaniline via in situ polymerization. Average crystallite sizes of the nanoparticles were estimated using Debye–Scherrer and Rietveld method and found to be in between 20-30 nm. FTIR spectra revealed the formation of interactions between the PANI molecules and the ferrite nanoparticles. Substitution of the nonmagnetic Zn ions considerably changes the magnetic properties of cobalt ferrites as observed from the M-H loops recorded by VSM at room temperature. The EMI-shielding performance of the fabricated composites was examined at various thicknesses with the polymer filler ratio of 1:1 in X-band frequency region using a vector network analyser. The EMI shielding performance of composites was found to be increasing with the thickness of composites where a thickness of 3.0 mm achieved an SE of ∼ 100 dB for the Co0.7Zn0.3Fe2O4-PANI composite. Composite absorbers were deposited on cotton fabrics for protective clothing by in situ incorporation during the synthesis of composites which displayed relatively high EMI shielding effectiveness (SE) (40-45 dB) at a thickness of only 0.30 mm for the fabrics. The PANI-Ferrite nanocomposites can be established as promising high capacity electromagnetic shielding materials because of the dipole polarization and the magnetic losses with low cost, lightweight, high durability and good flexibility.

Removal of Ferrimagnetic ZnFe2O4 Impurity Phase by Li Co-Doping in Fe Doped ZnO

A simple approach is presented to remove the impurity phase of ZnFe2O4 from Fe doped ZnO. Gradual incorporation of non-magnetic Li ions reduced 5.6% phase contamination of ZnFe2O4 to negligible limit (<0.01%) from 4 at% (atomic %) Fe doped ZnO. X-ray absorption near edge spectroscopy (XANES) revealed that the most of the Fe ions were in Fe3+ state. The optical absorption spectra of Fe doped ZnO samples exhibited d-d transition between Fe ions. It also indicated the signature of ZnFe2O4 phase, which reduced gradually on Li increment. ZnFe2O4 contained samples exhibited strong magnetic ordering with spin-glass character at low temperature and weak ferromagnetism (FM) at the room temperature with disordered inverse spinel structure. However, 6 at% Li incorporated sample did not show any significant FM in the entire temperature range of 2–300 K. ZnFe2O4 is supposed to be the possible source of the observed strong magnetic ordering i.e., FM has extrinsic origin. The gradual removal of impurity phase ZnFe2O4 by increasing Li doping without damaging any intrinsic property of Fe doped ZnO is primarily due to gradual increase of tetrahedral coordination of Fe ions.

Cooperation effect of indium and vanadium co-doped into bismuth-iron garnets on magnetic properties

For achieving tunable saturation magnetization and line width, different cations were doped into the YIG-based garnets, which the standard molecular formula could be expressed as A3[Fe2−xMx](Fe3−yNy)O12. Most researchers have reported a single rule of one element doping (x or y) on its magnetic properties. However, the cooperation effect of x + y to the magnetic contribution was not clearly clarified. In this work, multi-doped bismuth-iron garnets {Bi0.84Ca2.16}[Fe2−xInx](Fe3−yVy)O12 (x = 0.72–0.14 and y = 1.24–1.38) with low saturation magnetizations (4πM s = 200–600 Gs at 298 K) were prepared by a conventional fluxing agent method. The cooperation effect of In3+ and V5+ co-doped into bismuth-iron garnets (BIG) on their structures and magnetic properties were systematically investigated using XPS, TEM and VSM. It could be found that the total doped concentration (x + y) was decreasing regardless of the increasing V concentration (y) and decreasing In concentration (x). As-synthesized BIG presented a well single-crystal structure, and the lattice spacing was decreasing with the decrease of x + y in accompanying with the transition of dislocations from point defects to edge dislocations. Both linear increase of Curie temperature and 4πM s with the decrease of x + y was revealed. The mechanism could be attributed that the doped non-magnetic ions could reduce the average nearest-neighbor coordination irons for oxygen ions and weaken the anti-ferromagnetic super-exchange interactions among the magnetic ions within the structure, namely dilution effect. By comparison, the total concentraions were higher than that of previous works, which the tailorable 4πM s of ferrite was not reported. Here we revealed the controllable 4πM s with higher total concentrations (x + y ≥ 1.52). These findings will be provided more opportunities for applications in microwave devices.

Robust ferromagnetic and fast sunlight photocatalytic properties of nanocrystalline SnO2: Co/Cu codoping

Spintronics technology and organic pollutants removing have pushed the researchers to explore strong ferromagnetic and sunlight photocatalytic properties in oxide semiconductors. Herein, the role of Co monodoping and Co/Cu codoping on room temperature ferromagnetism and sunlight photodegradation properties of SnO2 nanoparticles was investigated. Series compositions composed of SnO2, Sn0.97Co0.03O2, Sn0.94Co0.03Cu0.03O2 and Sn0.91Co0.03Cu0.06O2 nanopowders were synthesized by coprecipitation method. The synthesized powders showed a single phase nature of tetragonal rutile structure with no sign for any impurities or secondary phases. SEM images demonstrate that the grains of the pure SnO2 consist of large aggregates which are transformed to fine particles due to Co/Cu codoping. The UV band gap of SnO2 was strongly engineered to visible light responses due to incorporation of Co/Cu ions. Integration between Co (magnetic) and Cu (nonmagnetic) ions induces clear room temperature ferromagnetism in SnO2. The exchange interactions between localized spins of Co3+-Co3+ Co3+-Cu2+ and Cu2+-Cu2+ via high-density doping-induced defects (oxygen vacancies) lead to strong ferromagnetic ordering. Sn0.94Co0.03Cu0.03O2 and Sn0.91Co0.03Cu0.06O2 nanopowders revealed a fast sunlight photocatalytic performance (~100%) for Congo red (CR), malachite green (MG) and methylene blue (MB) dyes. The partial substitution of Sn4+ by Co3+ and Cu2+ are found to augment the wavelengths absorbed, amount of oxygen vacancies and life time of the photo-generated electron hole pairs, resulting in better photocatalytic activity of Sn0.94Co0.03Cu0.03O2 and Sn0.91Co0.03Cu0.06O2 nanopowders in comparison with undoped and Co monodoped SnO2.

Coexistence of non-Fermi liquid behavior and biquadratic exchange coupling in La-substituted CeGe: Nonlinear susceptibility and DFT+DMFT study

Studies connected with the investigations of non-Fermi liquid (NFL) systems continue to attract interest in condensed matter physics community. Understanding the anomalous physical properties exhibited by such systems and its related electronic structures is one of the central research topics in this area. In this context, Ce-based and Ce-site diluted (with non-magnetic ions) compounds provide a fertile playground. Here, we present a detailed study of non-linear DC susceptibility and combined density functional theory plus dynamical mean field theory (DFT+DMFT) on Ce0.24La0.76Ge. Theoretical investigation of 4f partial density of states, local susceptibility and self-energy demonstrates the presence of NFL behavior which is associated with fluctuating local moments. Non-linear DC susceptibility studies on this compound reveal that the transition from NFL state to the new phase is due to development of the bi-quadratic exchange coupling and it obeys the non-linear susceptibility scaling. Under the application of magnetic fields, local moments interact spatially through conduction electrons resulting in magnetic fluctuations. Our studies point to the fact that the origin of the observed bi-quadratic exchange coupling is due to the spatial magnetic fluctuations.

Tuning the magnetocaloric effect in the Lu-doped frustrated Shastry-Sutherland system TmB4

$\mathrm{Tm}{\mathrm{B}}_{4}$ is an anisotropic, metallic magnetic system with geometrical frustration of the Shastry-Sutherland type. Here an experimental study of the magnetocaloric effect (MCE) in Lu-doped $\mathrm{T}{\mathrm{m}}_{1\ensuremath{-}x}\mathrm{L}{\mathrm{u}}_{x}{\mathrm{B}}_{4}$ ($x=0.06$, 0.30), evaluated from the temperature dependence of heat capacity and magnetization curves at 2 K, is presented. The results are described within a theoretical model based on an extended Ising Hamiltonian which considers interactions up to the fourth-next-nearest neighbors. Model parameters were optimized to achieve the best match to the experimental results over the whole range of $\mathrm{L}{\mathrm{u}}^{3+}$ ion concentrations. After optimization a good quantitative agreement with the adiabatic temperature change and a good qualitative agreement with magnetization curves is obtained. Our study shows that the efficiency of the MCE can be tuned by dilution with nonmagnetic Lu ions. The theoretical model developed could be used to design new magnetocaloric materials.

Enhancement of structure, dielectric and magnetic properties of nanocrystalline Mn–Zn ferrites using Ni–Ti ions

The present work concerned with the effect of substitution of Fe3+ magnetic ion by magnetic and nonmagnetic ions together, Ni2+–Ti4+ ions. Ferrite samples with general formula Mn0.9Zn0.1NiyTiyFe2-2yO4 (0.0 < y ≤ 0.25) were prepared using conventional ceramic technique. Single phase cubic spinel structure of the studied samples was confirmed using X-ray diffraction pattern. The surface morphology and compositional features of the prepared samples were studied using scanning electron microscope (SEM) and EDAX measurements. The porosity and lattice parameter of the samples are calculated as a function of Ni–Ti concentration. Temperature, frequency and compositional dependence of the dielectric constant (e`), ac resistivity (ρ) and dielectric loss tangent (tan δ) were studied. All the samples give the normal dielectric behavior of ferrites with temperature and frequency. The experimental results indicate that e`, tan δ and ρ decrease as the frequency increase. This behavior was discussed on the basis of Maxwell–Wagner model and Koops theory. The imaginary part of dielectric modulus (M``) was calculated and plotted as a function of temperature. The hysteresis loop parameters were measured as a function of Ni–Ti content using VSM. The obtained results revealed that the dielectric properties of Mn–Zn ferrites enhanced by increasing Ni–Ti concentration where the ac resistivity increased 7 times and the dielectrics loss tangent reduced by 95% of un-substituted Mn–Zn ferrite. The present work indicates also that the sample Mn0.9Zn0.1Ni0.1Ti0.1Fe1.8O4 shows high ac resistivity, low dielectric loss and high magnetization and most suitable for microwave applications

Average magnetization of quasi-binary solid solution of magnetic and non-magnetic ions

The paper describes features of calculating the magnetization of solid solution based on statistical approach on the example of a one-dimensional crystal. Calculations are made in approximation of Weiss effective field. The result shows the error of the third Gilleo hypothesis, which is still widely used to forecast the magnetic properties of solid solutions.

Anisotropic superexchange through nonmagnetic anions with spin-orbit coupling

Anisotropic superexchange interaction is one of the most important interactions in realizing exotic quantum magnetism, which is traditionally regarded to originate from magnetic ions and has no relation with the nonmagnetic ions. In our work, by studying a multi-orbital Hubbard model with spin-orbit coupling on both magnetic cations and nonmagnetic anions, we analytically demonstrate that the spin-orbit coupling on nonmagnetic anions alone can induce antisymmetric Dzyaloshinskii-Moriya interaction, symmetric anisotropic exchange and single ion anisotropy on the magnetic ions and thus it actually contributes to anisotropic superexchange on an equal footing as that of magnetic ions. Our results promise one more route to realize versatile exotic phases in condensed matter systems, long-range orders in low dimensional materials and switchable single molecule magnetic devices for recording and manipulating quantum information through nonmagnetic anions.

Influence of Zn-Zr substitution on the crystal chemistry and magnetic properties of CoFe2O4 nanoparticles synthesized by sol-gel method

The Zn-Zr co-substituted cobalt ferrite nanoparticles (CoZnxZrxFe2-2xO4, x = 0.0˗0.4) were synthesized by sol gel auto combustion route. The formation of cubic phase of Co ferrite was revealed from the X-ray diffractograms of the powder samples. The additional α-Fe2O3 and ZrO2 phases were occurred for ≥20% Zn-Zr substitution. The lattice parameters obtained by extrapolating Nelson–Riley function shows increase in its values with the Zn-Zr substitution. The particle size shows increasing trend with the Zn-Zr substitution. The cation distribution obtained from the Rietveld refinement of XRD estimate the equal preference of Zn ons preferred tetrahedral A site whereas most of the Zr ions occupy octahedral B site. The decrease in Fe ions with the Zn-Zr substitution resulted in the decrease in coercivity and saturation magnetization of the ferrites. Zero field cooled and field cooled magnetization plots of the ferrites reveals the ferromagnetic behaviour of the prepared ferrite samples. The blocking temperature does not vary significantly with the varying Zn-Zr substitution. The Mössbauer study confirms the weakening of the magnetic linkages between cations at A and B sites, due to the substitution of non-magnetic Zn-Zr ions for magnetic Fe ions. The decrease in coercivity with moderate saturation magnetization could make this material suitable for electronic devices.

Spin-density studies of the multiferroic metal-organic compound [NH2(CH3)2][FeIIIFeII(HCOO)6

Polarized neutron diffraction is used to study in depth the magnetic properties of the heterometallic compound [NH2(CH3)2][FeIIIFeII(HCOO)6] and give insight into its magnetic behaviour, addressing open questions that will contribute to a better understanding of this attention-grabbing material and other related ones. Previous results revealed that upon cooling, the magnetic moments of the FeII and FeIII sites do not order simultaneously: the magnetization of the FeII site increases faster than that of the FeIII sites. Unpolarized neutron diffraction measurements at 2 K with no external field revealed some discrepancies in the saturation value of the magnetic signal on the FeIII sites and in the ferromagnetic moment along the c axis. These discrepancies could be related to the actual distribution of magnetic moment, since unpolarized neutron diffraction gives information on the magnetic moment localized only on the magnetic ions. Polarized neutron diffraction allows an analysis of the magnitude of the spin density over magnetic and non-magnetic ions (the organic ligand and the counterion), which can give a clue to explain the low saturation on the FeIII sites and the correlation with the physical measurements. The present study also contributes to the understanding of the magneto-electric behaviour of this compound, giving insight into the role of metal disorder in the origin of the structural phase transition, which is responsible for its antiferrolelectric order, and into the influence of spin-density delocalization on its magneto-electric properties, allowing a discussion of the alternative explanations given so far for its electric properties at low temperature.