Ferrimagnetic Curie Temperature Research Articles

Mössbauer studies on titanium substituted molybdenum ferrite

Mössbauer spectra of Fe2Mo1−xTixO4 (0.2≤x≤1.0) spinel oxides were recorded at 295K in their paramagnetic state. The spectra of all the samples show asymmetric quadrupole split pattern and as molybdenum is progressively replaced by titanium the pattern becomes more and more symmetric. The isomer shift and quadrupole splitting values, inversion parameter and the ratio of Fetotal3+/Fetotal2+ have been calculated from a least-square fitting program. Substitution of molybdenum by titanium in Fe2MoO4, reduces the total Fe3+ and the extent of Fe3+ reduction on tetrahedral (A) and octahedral (B) sites are different. The amount of FeA3+ and FeB3+ions in the x=0.4 and x=0.6 ferrite samples are the same, but their ferrimagnetic Curie temperatures are different, and the former has a compensation temperature which is absent in the latter. This is due to the participation of Mo3+ in the magnetic interactions, which is present in Fe2MoO4, along with Mo4+.

Magnetic studies on Zn-substituted molybdenum ferrite

Syntheses, characterization and magnetization measurements were carried out on the ferrites, Fe 2− x Zn x MoO 4 (0.0⩽ x⩽1.0). Substitution of Fe 2+ by Zn 2+ ions in Fe 2MoO 4 shows some interesting results in the field-cooled (FC) and zero-field-cooled (ZFC) magnetization measurements. For x⩾0.2, the samples do not show a compensation temperature ( T K) below the ferrimagnetic Curie temperature ( T C). The change in the T C is small for samples with x⩽0.4. For values of x⩾0.6, the samples show a very sharp decrease in T C as a complex magnetic order sets in the B-site due to very weak A–O–B interactions. For samples x⩾0.6, the ZFC magnetization drops to zero with temperature approaching 0 K, characteristic of cluster glass or spin glass materials.

Covalency effect of Ge-substitution on anisotropic thermal expansion in Mn 7Sn 4 and Mn 7Sn 3Ge

The lattice parameters a( T) and c( T) as a function of temperature T for Mn 7Sn 4 and Mn 7Sn 3Ge with the Ni 2In-type crystal structure have been measured. In both materials, the anomalous thermal expansions in a( T) and c( T) are observed in an anisotropic fashion at the ferrimagnetic Curie temperature but in an isotropic one at the spin-glass-like transition temperature. The obtained results are qualitatively discussed from a viewpoint of the band picture and the difference in covalency between Sn and Ge atoms.

Long-Time Decay of Thermoremanent Magnetization through Stepwise Changes of the Reentrant Spin-Glass-Like State in the Ni2In-Type Mn7Sn4

The zero-field-cooled magnetization at the magnetic field H = 300 Oe shows anomolous kinks at T A and T e (> T A ) far below the reentrant spin-glass-like transition temperature T f (above which a long-range ferrimagnetic ordering is set up). The irreversibility between the zero-field-cooled and the field-cooled magnetizations, and the time decay of the thermoremanent magnetization (σTRM) are observed below the ferrimagnetic Curie temperature T C . The decay feature can be described by Ogielski's power law σTRM = At -a whose a exhibits peaks at T A , T B , T f and T C . The peak of α at Te can be fitted by the combination of Ising type and Ginzburg-Landau type expressions. Three stepwise changes of the spin-glass-like state below T f and the feature of the coexistence of short-range spin-glass and long-range magnetic ordering components above T f are discussed.

Structure and magnetic properties of quenched (Mn/sub x/Al/sub 1-x/)/sub 3/O/sub 4/ spinels and Hausmannites

Manganese aluminate spinels and Hausmannites, namely (Mn/sub x/Al/sub 1-x/)/sub 3/O/sub 4/, with compositions varying between x=0.33 and x=1.00 have been synthesized by sintering of MnO and Al/sub 2/O/sub 3/ mixtures. Lattice parameters of these spinels and Hausmannites increase linearly with increasing Mn content and depend on neither sintering temperature nor cooling rate. Magnetic hysteresis loops at 5 K show non-saturating features up to 5 T. Ferrimagnetic Curie temperatures of spinels and Hausmannites both increase monotonically with increasing Mn content.

Nonlinear Pressure Dependences of the Ferrimagnetic Curie and the Ferrimagnetic-to-Antiferromagnetic Transition Temperatures in (Cr1-xTix)5S6

The ferrimagnetic Curie temperature ( T c ) and the ferrimagnetic-to-antiferromagnetic transition temperature ( T t ) in (Cr 1- x Ti x ) 5 S 6 (0≤ x ≤0.15) were investigated up to 14 kbar. It is revealed that T c decreases nonlinearly with increasing pressure ( P ) and that T t also decreases at high pressures. The ratio T t ( P )/ T c ( P ) increases with increase in P . These nonlinear pressure dependences of T c ( P ) and T t ( P ) are qualitatively discussed on the basis of the band structure calculation for CrS in which the stability of antiferromagnetic states is determined by Cr3 d z 2 -Cr3 d z 2 and Cr d -S p interactions. Important role of Cr d -S p hybridization on the pressure effect is suggested.

Influence of the substitution of Cu ions for Cd ions on the crystallographic and magnetic properties of Cd 1− xCu xCr 2Se 4 spinels

All the compounds under study show the spinel normal structure. The lattice parameters decrease with an increase in the Cu concentration. The samples with low Cu concentrations ( x ≤ 0.2) exhibit ferrimagnetic ordering and Curie temperatures of 150 K. The samples with high Cu concentrations ( x ≥ 0.9) are ordered ferromagnetically, and their Curie temperatures are much higher and close to 480 K. Moreover, for the four samples under investigation one can observe a significant lowering of the saturation magnetic moment in comparison with the theoretical one. This lowering seems to be connected with the high degree of defects in the crystal structure. An attempt is made to interpret this fact with the use of the vacancy parameter.

Pressure Effect on the Magnetic Transition Temperatures of Mn7Sn3Ge and Mn7Sn2Ge2

The pressure (P) derivative of the ferrimagnetic Curie temperature dTC/dP for the Ni2In-type Mn7Sn4-zGez is determined to be dTC/dP=(1.8±0.1)-(0.4±0.1)z K/kbar. The signs of the pressure derivatives dTf/dP are negative for z=0 and 0.4, where Tf is the transition temperature from the spin-glass like state to the ferrimagnetic one. These pressure effects are discussed on the basis of the interaction curve for antiferromagnetic Mn alloys.

Magnetic properties of Ni1−x Cu x Cr2O4(0⩽x⩽1) compounds

The compounds Ni1−x Cu x Cr2O4 (0⩽x⩽1) have been synthesised by solid-state reaction between basic nickel(II) carbonate, basic copper(II) carbonate and chromium (III) carbonate in required molar ratios at 800±10°C for 20 hr. The reaction products have been characterized by chemical analyses and powder x-ray diffraction patterns. Magnetic susceptibility has been measured in the temperature range of 300–900 K at 10 kOe. All the products show ferrimagnetic behaviour with the ferrimagnetic Curie temperature (T c) in the range of 50–150 K. The curie temperature increases when copper(II) ion is substituted for nickel(II) ion in NiCr2O4. The experimental values of the average effective magneton number (p-0304;) agree with theoretical values.

Magnetic Susceptibility of Pressed Powders of Some Rare-Earth Iron Garnets

Abstract The molar magnetic susceptibilities (χм) of spherical balls of rare-earth iron garnets REIG's, with RE = Y, Gd, Dy, Ho, Er and Yb, prepared from pellets pressed at pressures ranging from 2 to 8 × 107 kg m-2 , have been measured in the temperature range 300-900 K. It is found that χмα exp( - f), where f is the pore fraction of the pressed balls. It has also been observed that χм for a particular garnet at a fixed temperature increases from powder through pressed material to single crystal. REIG's reveal typical ferrimagnetic behaviour with the ferrimagnetic Curie temperature (Tc) lying in the range 550-570 K for single crystals. In general, for pressed material Tc increases linearly with density. The χм -1 vs, T variation has been analysed using molecular field theory. It has been found that for T ≫ Tc the magnetic ions behave as if they were almost free and yield a magneton number very close to their free ion value.

Electrical transport in gadolinium iron garnet (GdIG)

Thermoelectric power [Formula: see text] and electrical conductivity (σ) of Gd3Fe5O12 (gadolinium iron garnet GdIG) have been reported in the temperature range 500 to 1200 K. [Formula: see text] remains almost constant between 600 and 1100 K but it increases with decrease of temperature in accordance with the relation[Formula: see text]Conductivity changes by a factor of five near the ferrimagnetic Curie temperature (Te = 564 K). The log σ vs. T−1 curve also has a break at 900 K. Besides this jump and break the log σ vs. T−1 plot is linear and slopes of these lines correspond to activation energies of 0.55 eV for T < 560 K, 0.75 eV for the temperature range 575–900 K, and 0.92 eV between 900 and 1200 K. It has been concluded that electric conduction up to 1200 K in this compound is extrinsic. Between 575 and 1200 K it is due to hopping of holes from Fe4+ to Fe3+ sites and below 560 K it is due to the band conduction of holes in the valence (O2−, 2p) band.

Computer Simulation of Temperature and Field Dependences of Sublattice Magnetizations and Spin-Flip Transition in Gallium-Substituted Yttrium Iron Garnet

On the basis of the molecular field model, sublattice magnetizations in gallium-substituted yttrium iron garnet Y 3 Ga x Fe 5- x O 12 are calculated over a wide range of x , temperature and applied magnetic field with a computer program. Comparing the calculated temperature dependence of spontaneous magnetization, the critical fields of the spin-flip transition at high magnetic fields and the ferrimagnetic Curie temperature, with experimental data, the super-exchange coefficients in YIG and Y 3 Ga x Fe 5- x O 12 were evaluated.

Thermal Expansion Behaviour through the Magnetic Transition in Cr5S6

Lattice parameters of hexagonal Cr 5 S 6 have been determined as a function of temperature by X-ray diffraction between 80 K and 400 K. Marked changes in temperature slope for c - and a -axes appear at the noncollinear-to-collinear transition temperature T t =(167±2) K and at the ferrimagnetic Curie temperature T c =(310±5) K. The slope of c -axis changes from negative to positive at T t as the temperature is raised. Observed changes in slope for cell volume at T t and T c agree with those calculated from the Ehrenfest relation. This correspondence is consisted with the second order characteristics predicted theoretically by Dwight et al. Positive amounts of departure from usual thermal expansions for phonons are observed on both axes below T c , which are well explained in terms of exchange striction.

Effect of pressure on the Néel and the ferrimagnetic Curie temperatures of FeS1+δ

physica status solidi (a)Volume 24, Issue 1 p. K31-K34 Short Note Effect of pressure on the Néel and the ferrimagnetic Curie temperatures of FeS1+δ S. Anzai, S. Anzai Faculty of Engineering, Keio University, Yokohama-shiSearch for more papers by this authorK. Ozawa, K. Ozawa Japan Atomic Energy Research Institute, Tokai-muraSearch for more papers by this author S. Anzai, S. Anzai Faculty of Engineering, Keio University, Yokohama-shiSearch for more papers by this authorK. Ozawa, K. Ozawa Japan Atomic Energy Research Institute, Tokai-muraSearch for more papers by this author First published: 16 July 1974 https://doi.org/10.1002/pssa.2210240144Citations: 8AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume24, Issue116 July 1974Pages K31-K34 RelatedInformation

Effects of Fluoride Addition on Sintering and Magnetic Properties of Mn<sub>1.29</sub>Fe<sub>1.71</sub>O<sub>4</sub> Ferrite

Effects of addition of fluorides, MnF2 and FeF3⋅3H2O, on the sintering of Mn1.29Fe1.71O4 ferrite compact and magnetic properties of the fired ferrite body were studied by measuring the fired bulk density, grain size, B-H curve (magnetic hysteresis curve), ferrimagnetic Curie temperature, saturation magnetization and crystal lattice constant. The results obtained are as follows.1) By addition of the fluorides, grain size and bulk density of the fired ferrite body became larger.2) No fluorine was contained in the fired ferrite body, since all the amount of fluorine had been liberated during the firing.3) No ferrimagnetic Curie temperature, saturation magnetization and crystal lattice constant being intrinsic properties of ferrite were changed with addition of the fluorides.4) By addition of the fluorides, magnetic hysteresis characteristics depending on the compactness of the ferrite materials were changed, i.e., magnetic flux density became larger and coercive force became smaller.

Effect of Pressure on the Ferrimagnetic Curie Temperature of Fe3□ Se4

physica status solidi (a)Volume 19, Issue 1 p. K39-K41 Short Note Effect of Pressure on the Ferrimagnetic Curie Temperature of Fe3□ Se4 K. Ozawa, K. Ozawa Japan Atomic Energy Research Institute, Tokai-muraSearch for more papers by this authorT. Yoshimi, T. Yoshimi Faculty of Engineering, Keio University, Hiyoshi, Yokohama-shi(2)Search for more papers by this authorS. Anzai, S. Anzai Japan Atomic Energy Research Institute, Tokai-muraSearch for more papers by this authorS. Yanagisawa, S. Yanagisawa Japan Atomic Energy Research Institute, Tokai-muraSearch for more papers by this author K. Ozawa, K. Ozawa Japan Atomic Energy Research Institute, Tokai-muraSearch for more papers by this authorT. Yoshimi, T. Yoshimi Faculty of Engineering, Keio University, Hiyoshi, Yokohama-shi(2)Search for more papers by this authorS. Anzai, S. Anzai Japan Atomic Energy Research Institute, Tokai-muraSearch for more papers by this authorS. Yanagisawa, S. Yanagisawa Japan Atomic Energy Research Institute, Tokai-muraSearch for more papers by this author First published: 16 September 1973 https://doi.org/10.1002/pssa.2210190151Citations: 7AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume19, Issue116 September 1973Pages K39-K41 RelatedInformation

Oxidizing reaction of MnMgCu ferrite accompanied with its decomposition

The oxidizing reaction accompanied with decomposition of manganese-magnesium ferrite containing a small amount of copper (Cu 0·08 6 Mg 0·21 4 Mn 0·98 6 Fe 1·71 4 O 4) was studied by quantitatively analysing the measured values of saturation magnetization, crystal lattice constant and ferrimagnetic Curie temperature. The samples were oxidized at various temperatures between 650° and 900°C for some hundreds of minutes in air, and the existing phases were identified by X-ray diffraction. It was recognized that, in the course of the oxidation reaction, the ferrite decomposes into spinel type ferrite and “non-magnetic” α-Fe 2O 3 and Mn 2O 3,and Mn 2O 3, and that decomposition decreases the saturation magnetization, crystal lattice constant and ferrimagnetic Curie temperature. From the obtained results it is concluded that the oxidizing reaction proceeds as follows: Cu 2+ 0·08 6 Mg 2+ 0·021 0 Mn 2+ 0·70 0 Mn 3+ 0·28 6 Fe 3+ 1·71 4 O 4 + δ 2 O 2 ⇌ 3(1 − x)δ Mn 2 O 3 + 1 f Cu 2+ 0·08 6f Mg 2+ 0·21 4f Mn 2+ (0·70 6 − 2δ)f Mn 3+ (0·28 6 − 4δ + 6xδ)f Fe 3+ (1·71 4 − 6xδ)f O 4, where f = 1 1−2δ , and x = 0· − 0·8.

Messung der Magnetfelder am Kernort von 152 Sm und 154 Sm im Sm6Mn23 mit Hilfe der Spinpräzessionsmethode / Measurement of the local magnetic field, at the site of Sm in Sm6Mn23 by the spin precession method

Abstract The magnetic field at the site of the nuclei 152 Sm and 154 Sm in a ferrimagnetic Sm6Mn23 probe has been measured by means of the perturbed angular correlation method after Coulomb excitation. The temperature dependence of the magnetic field has been investigated and compared with the results of macroscopic experiments. It can be concluded from the present work that the magnetic field Heff(T) at the site of the Sm nuclei is proportional to the macroscopic magnetisation J (T). We obtained a ferrimagnetic Curie Temperature of TC = 438(5) K in good aggreement with macroscopic values and Heff (T=0 K) = 1300(50) kOe.

Defect structure in oxygen-excess manganese-magnesium ferrite

Specific gravity, crystal lattice constant, saturation magnetization and ferrimagnetic Curie temperature were measured to clarify the type of point defects in the oxygen-excess manganese-magnesium ferrite containing a slight amount of copper (Cu 0·08 6 Mg 0·21 4 Mn 0·98 6 Fe 1·71 4 O 4+δ). Of those properties, crystal lattice constant and saturation magnetization decrease, while ferrimagnetic Curie temperature increases, as the oxygen content in the ferrite increases. Specific gravity is almost independent upon the oxygen content. From the quantitative analyses of these characteristics, it can be concluded that the point defects in oxygen-excess manganese-magnesium ferrite are of cation vacancies on its B-sites (octahedral sites).

Growth of mixed cation iron garnets in the ytterbium-gallium and yttrium-calcium silicate systems

Single crystals with the compositions (A) = Yb 3Fe 5 − xGa xO 12 with x varying from 0.5 to 4.0 and (B) = Y 2.9 − xBi 0.1Ca xFe 5 − x- Si xO 12 with x varying from 0.6 to 1.3 have been grown from flux. Crystals of compositions (A) are crystallized from a PbO/PbF 2 solvent, whereas crystals of compositions (B) are from a PbO/B 2O 3 solvent. The unit-cell dimensions, the ferrimagnetic Curie temperature and the segregation coefficients of Ga 3+ in (A) and Ca 2+ in (B) have been determined. The difference between the two fluxes is discussed.