Decrease Of Spontaneous Magnetization Research Articles

Synthesis, Structural, and Magnetic Properties of Nanocrystalline/Nanosized Manganese-Nickel Ferrite–${\rm Mn}_{0.5}{\rm Ni}_{0.5}{\rm Fe}_{2}{\rm O}_{4}$

The nanocrystalline/nanosized mixed manganese–nickel spinel ferrite ${\rm Mn}_{0.5}{\rm Ni}_{0.5}{\rm Fe}_{2}{\rm O}_{4}$ was successfully synthesized by the classical ceramic method followed by mechanical milling. The refinement of the crystallite size is obtained by increasing the milling time up to 120 min. The particles size distribution performed on the milled powder showed a fine ferrite powder. The Neel temperature of ${\rm Mn}_{0.5}{\rm Ni}_{0.5}{\rm Fe}_{2}{\rm O}_{4}$ decreases by increasing the milling time as a result of the structural disorder and it is larger when compared with the manganese ferrite one and lower when compared with the nickel ferrite one. The saturation magnetization of the spinel structure was found to be 2.42 $\mu_{B}$ and it is close to the theoretical one 2.5 $\mu_{B}$ . The saturation magnetization and spontaneous magnetization decrease by increasing milling time. The spontaneous magnetization is reduced more drastically when compared with the saturation magnetization. One of the major causes is assumed to be the spin canted effect induced at the particles surface by milling process.

Finite-size effects in amorphous Fe90Zr10/Al75Zr25multilayers

The thickness dependence of the magnetic properties of amorphous Fe90Zr10 layers has been explored using Fe90Zr10/Al75Zr25 multilayers. The Al75Zr25 layer thickness is kept at 40 \AA, while the thickness of the Fe90Zr10 layers is varied between 5 and 20 \AA. The thickness of the Al75Zr25 layers is sufficiently large to suppress any significant interlayer coupling. Both the Curie temperature and the spontaneous magnetization decrease non-linearly with decreasing thickness of the Fe90Zr10 layers. No ferromagnetic order is observed in the multilayer with 5 {\AA} Fe90Zr10 layers. The variation of the Curie temperature $T_c$ with the Fe90Zr10 layer thickness $t$ is fitted with a finite-size scaling formula $[1-\Tc(t)/\Tc(\infty)]=[(t-t')/t_0]^{-\lambda}$, yielding $\lambda=1.2$, and a critical thickness $t'=6.5$ \AA, below which the Curie temperature is zero.

Anomalous impurity effect on magnetization in frustrated one-dimensional ferro- and ferrimagnets

Significant decrease of spontaneous magnetization in frustrated one-dimensional ferro- and ferrimagnets due to nonmagnetic impurities is predicted. Using the density-matrix renormalization group method and the exact diagonalization method, we confirm that the total spin can vanish due to a single impurity in finite chains. Introducing the picture of magnetic domain inversion, we numerically investigate the impurity-density dependence of magnetization. In particular, we show that even with an infinitesimal density of impurities, the magnetization in the ground state is reduced by about 40% from that of the corresponding pure system. Conditions for the materials which may show this anomalous impurity effect are formulated.

Pressure-induced orbital ordering in magnetite above the verwey temperature

Thermomagnetic hysteresis of magnetization was found to occur in magnetite subjected to a heat treatment under an external pressure of 37.5 kbar. This effect is observed over the temperature range T < 640 K, and its magnitude is independent of the synthesis conditions. The decrease in spontaneous magnetization is explained by ferromagnetic ordering of the orbital magnetic moments under pressure.

Magnetovolume effect and magnetic properties ofDy2Fe17−xMnx

The structural and magnetic properties of ${\mathrm{Dy}}_{2}{\mathrm{Fe}}_{17\ensuremath{-}x}{\mathrm{Mn}}_{x}$ $(x=0--5)$ compounds have been investigated using x-ray diffraction, linear thermal expansion, magnetization measurements, and $^{57}\mathrm{Fe}$ M\ossbauer spectroscopy. Compared with ${\mathrm{Dy}}_{2}{\mathrm{Co}}_{17\ensuremath{-}x}{\mathrm{Mn}}_{x}$ compounds for which a linear increase of the unit-cell volume $V$ with increasing Mn fraction is found, the compositional dependence of the lattice parameters of ${\mathrm{Dy}}_{2}{\mathrm{Fe}}_{17\ensuremath{-}x}{\mathrm{Mn}}_{x}$ first exhibits a slight maximum around $x=0.5$ before increasing monotonically with further increase in $x$; this behavior can be ascribed to a spontaneous magnetostriction as confirmed by linear-thermal-expansion measurements. The Curie temperature ${T}_{C}$ remains essentially unchanged for Mn contents up to $x=1$ [${T}_{C}=370(4)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $x=0.0$, ${T}_{C}=373(4)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for $x=1.0$] before decreasing steadily with further increase in Mn content [${T}_{C}=232(4)\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ for ${\mathrm{Dy}}_{2}{\mathrm{Fe}}_{12}{\mathrm{Mn}}_{5}$]. The rapid decrease of spontaneous magnetization and the essentially constant value of ${T}_{C}$ for lower Mn concentrations can be understood in terms of the two-sublattice model and by considering the preferential site occupation of Mn atoms in the ${\mathrm{Dy}}_{2}{\mathrm{Fe}}_{17\ensuremath{-}x}{\mathrm{Mn}}_{x}$ unit cell. The exchange interaction between the rare-earth and transition-metal sublattices has been investigated by means of a mean-field analysis of the high-field magnetization isotherms which were measured on the powder samples. The $^{57}\mathrm{Fe}$ hyperfine interaction parameters of the ${\mathrm{Dy}}_{2}{\mathrm{Fe}}_{16}{\mathrm{Mn}}_{1}$ and ${\mathrm{Dy}}_{2}{\mathrm{Fe}}_{14}{\mathrm{Mn}}_{3}$ samples have been determined from the M\ossbauer spectra $(5--300\phantom{\rule{0.3em}{0ex}}\mathrm{K})$.

Lattice expansion and noncollinear to collinear ferrimagnetic order in aMnCr2O4nanoparticle

We report magnetic behaviour of MnCr$_2$O$_4$, which belongs to a special class of spinel, known as chromite. Bulk MnCr$_2$O$_4$ shows a sequence of magnetic states, which follows paramagnetic (PM) to collinear ferrimagnetic (FM) state below T$_C$ $\sim$ 45 K and collinear FM state to non-collinear FM state below T$_S$ $\sim$ 18 K. The non-collinear spin structure has been modified on decreasing the particle size, and magnetic transition at T$_S$ decreases in nanoparticle samples. However, ferrimagnetic order is still dominating in nanoparticles, except the observation of superparamagnetic like blocking and decrease of spontaneous magnetization for nanoparticle. This may, according to the core-shell model of ferrimagnetic nanoparticle, be the surface disorder effect of nanoparticle. The system also show the increase of T$_C$ in nanoparticle samples, which is not consistent with the core-shell model. The analysis of the M(T) data, applying spin wave theory, has shown an unusual Bloch exponent value 3.35 for bulk MnCr$_2$O$_4$, which decreases and approaches to 1.5, a typical value for any standard ferromagnet, with decreasing the particle size. MnCr$_2$O$_4$ has shown a few more unusual behaviour. For example, lattice expansion in nanoparticle samples. The present work demonstrates the correlation between a systematic increase of lattice parameter and the gradual decrease of B site non-collinear spin structure in the light of magnetism of MnCr$_2$O$_4$ nanoparticles.

Magnetic and thermal properties of Ni–Mn–Ga shape memory alloy with Martensitic transition near room temperature

We have studied the magnetic properties of an off-stoichiometric Heusler shape memory alloy Ni 51.9Mn 23.2Ga 24.9 with near room temperature martensitic transition at 306 K. The temperature dependence of magnetization revealed a thermal hysteresis and a ∼10% decrease in spontaneous magnetization across the martensitic transition. In-situ X-ray diffraction measurements at different temperatures revealed a negative shape strain of 4.8%. Heat absorptions measurements indicated that the martensitic structural transition may take place in multiple steps.

Magnetic anisotropy evolution of (Ce,Y) 2Co 17 compounds

The evolution of the magnetic anisotropy of (Ce,Y) 2Co 17 compounds with increasing Ce concentration was investigated by magnetic measurements and X-ray diffraction on magnetically aligned powders. At room temperature the easy magnetization direction changes from perpendicular to the c-axis to parallel to the c-axis with increasing Ce concentration. A spin-reorientation transition from easy-axis anisotropy at higher temperatures to easy-plane anisotropy at lower temperatures arises at about 600, 530 and 320 K in Ce 1.3Y 0.7Co 17, Ce 1.5Y 0.5Co 17 and Ce 1.7Y 0.3Co 17, respectively. The Curie temperature and spontaneous magnetization decrease with increasing Ce concentration. These magnetic behaviours are discussed in terms of the itinerant 4f states of Ce ion and the hybridization between the cobalt 3d states and the cerium 4f states.

Magnetic properties of (Pr1−xCex)6Fe13Al compounds

Samples of (Pr1−xCex)6Fe13Al (x=0.1, 0.2, 0.3, 0.4, 0.5, and 0.6) were prepared by arc melting and annealed for two weeks at 973 K. The x-ray diffraction patterns show that all the samples crystallize with the Nd6Fe13Si-type structure. The unit-cell volume increases first and then decreases as the Ce content increases. The Curie temperature and the spontaneous magnetization decrease almost linearly with increasing Ce concentration, supporting the existence of a mixed valence of Ce3+ and Ce4+. The series is ferromagnetic at high temperature; however, the peak at low temperature of the M–T curve most likely corresponds to spin-glass behavior.

Structure and magnetic properties of (Nd1−xCex)6Fe13Al compounds

Samples of (Nd1−xCex)6Fe13Al (x=0.1, 0.2, 0.3, 0.4, 0.5, 0.6) were prepared by arc melting and annealed for 2 weeks at 700 °C. The x-ray diffraction patterns for the (Nd1−xCex)6Fe13Al samples show that all the above-mentioned samples crystallize with the Nd6Fe13Si-type tetragonal phase. The unit-cell volume v increases first and then decreases as the Ce content increases. The Curie temperature and the spontaneous magnetization decrease almost linearly with increasing Ce concentration. All these prove the existence of the mixed valence of Ce3+ and Ce4+. A complicated temperature dependence of magnetization is observed. Although the series is ferromagnetic at high temperature, there is a low-temperature peak in each M–T curve, which is in agreement with spin-glass behavior. This phenomena is reported in 6:13:1-type compounds.

Magnetization and magnetocrystalline anisotropy of R2Fe17 intermetallics under pressure

The measurements of magnetization and magnetic anisotropy of R2Fe17 (R=Y, Er, Ho, and Gd) single crystals were performed under hydrostatic pressure up to 1 GPa, in temperature range 5–300 K and at magnetic fields up to 5 T, using the SQUID magnetometer with a miniature pressure CuBe cell. A pronounced decrease of spontaneous magnetization M of the R2Fe17 intermetallics has been observed under pressure. The values of dM/dp vary in an interval from −0.32μB/f.u. per kbar (Y2Fe17) up to −0.1μB/f.u. per kbar (Ho2Fe17). The R elements in the R2Fe17 intermetallics have a strong influence on the d(ln mFe)/dp values at 5 K. A remarkable decrease of the anisotropy constant with pressure, d ln K1/dp=−1.7×10−2 kbar−1 at 5 K, was observed on the Y2Fe17 compound. In the Gd2Fe17 compound, |K1(T)| increases with increasing pressure below 150 K and decreases with increasing pressure above this temperature value. The critical field HC(T) of the FOMP in the Er2Fe17 compound exhibits a similar behavior, it increases under pressure at temperatures below 60 K and decreases at higher temperatures.

Temperature dependence of optical conductivity in double-exchange ferromagnetLa1−xSrxMnO3

The optical absorption observed in ferromagnetic metal ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ shows a strong temperature dependence. Assuming that the temperature dependence comes mainly from the spontaneous magnetization, we study theoretically how the optical conductivity is affected by the decrease of spontaneous magnetization. The coherent-potential approximation is used to describe the effect of ${t}_{2g}$ spin disorder on the optical conductivity, which consists of intraband and interband transitions within ${e}_{g}$ bands. The result explains well some important features of the experimental data.

Ｃｒ添加によるα‐Ｆｅ２Ｏ３の寄生強磁性の低減

We performed magnetization measurements on a soft magnetic film deposited on a substrate made of α-Fe2O3,which is a candidate material for the sliders of magnetic heads because of its excellent tribological properties. Since α-Fe2O3 exhibits the spontaneous magnetization due to the weak ferromagnetism at room temperature, a biased field caused by magneto-static coupling between the magnetic film and the substrate was observed in the hysteresis loop.In order to use α-Fe2O3 as a magnetic core substrate, we reduced the spontaneous magnetization by synthesizing a solid solution of α-Fe2O3 and Cr2O3, (CrxFe1-x)2O3. Magnetization measurements revealed that the decrease in spontaneous magnetization with increasing x is larger than that expected from simple dilution with non-magnetic ions.This behavior may be attributed to the effect of the single ion type anisotropy of Cr3+ affecting on the spin direction of Fe3+.

The influence of pressure on spontaneous magnetization of Fe60Mn20B20amorphous alloy at temperature range 77.4–300 K

Abstract Amorphous, ferromagnetic, invar like, Fe60 Mn20 B20 alloy has been investigated. Two kinds of experiments were carried out for this alloy. The first, using high pressure technique, revealed the influence of pressure on B(H) dependencies within the wide range of temperature under pressure of 0.5 GPa. From the magnetization curves obtained during these experiments the decrease of spontaneous magnetization caused by applied pressure 0.5 GPa at temperature -180°C has been calculated at the rate about 7 10−11T/Pa. In the second kind of experiments the measurements of volume magnetostriction up to 720 kA/m magnetic field intensity have been done. Volume magnetostriction coefficient at temperature 77.4 K has been determined to be about 2 10−11 [A/m]−1.

Spontaneous magnetization of Fe - Mn - B Amorphous alloys under high pressures

Abstract We have investigated the influence of high pressure (up to 2 GPa) on the spontaneous magnetization of six Fe80-x Mnx B20 alloys (x = 6, 10, 15, and three alloys with x close to 20). In all cases a decrease of spontaneous magnetization with pressure was noticed, in some considerable.

Magnetic Properties of (Cr1-xNix)2P Compounds

Measurements of magnetization and magnetic susceptibility were made on compounds (Cr 1- x Ni x ) 2 P (0.35 ≤ x ≤1). These compounds have an orthorhombic structure for 0.35 ≤ x ≤0.5 and a hexagonal structure for x ≥0.55. In the orthorhombic phase, the compounds are ferromagnetic for 0.45 < x ≤0.5 and paramagnetic for 0.35 ≤ x ≤0.43. The Curie temperature and the spontaneous magnetization decrease rapidly with decreasins x . The Curie constant is almost independent of x . For the hexagonal structure, the compounds are Pauli paramagnets.

Magnetic properties of compounds (Mn,Cr) 1+ xSb, V 1+ xSb and (Mn,V) 1+ xSb with B8-type structures

Investigations of the compounds (Mn,Cr) 1+ x Sb, V 1+ x Sb and (Mn,V) 1+ x Sb with B8-type structures are described. The homogeneity ranges of (Mn,Cr) 1+ x Sb and (Mn,V) 1+ x Sb shift to metal-richer compositions with increasing temperature. These compounds are ferrimagnetic. The magnetic-ordering temperature and the spontaneous magnetization decrease with increasing Cr Mn and V Mn ratios, respectively. The homogeneity range of the high-temperature phase V 1+ x Sb is situated around the composition x = 0.40. V 1.40Sb shows nearly temperature-independent (Pauli) paramagnetism (except at low temperature).

Spontaneous magnetization from NMR measurements and critical exponents in nickel

Nuclear magnetic resonance of Ni61 has been studied in pure nickel metal (of natural isotope composition) in the vicinity of the Curie point. The temperature dependence of NMR frequency has been measured up to 0·96Tc. Determination ofTc was aided by initial susceptibility measurements. The analysis of these results yields β=0·336±0·002 for the critical exponent describing the decrease of spontaneous magnetization to zero atTc. This value ofβ is in excellent agreement with the corresponding values obtained from NMR experiments in ferromagnetic EuS and antiferromagnetic MnF2, it differs, however, from the values obtained for nickel by other methods. In a general discussion of this problem which uses the theoretical relations between various critical exponents the earlier data, in particular those of Weiss and Forrer, are reexamined.

Magnetic Properties of Fe65(Ni1-xMnx)35 Ternary Alloys

Magnetic properties of Fe 65 (Ni 1- x Mn x ) 35 ternary alloys which have the f.c.c. structure over the whole range of x were investigated. It was found that the alloys are antiferromagnetic in the composition range of 1≥ x >0.3 and are ferromagnetic in the composition range of 0≤ x <0.3. In the ferromagnetic region, the Curie temperature and the spontaneous magnetization decrease rapidly with increasing x or with the decrease of mean electron concentration. Many physical properties of the alloys are discussed on the basis of three postulates, i.e. , 1) electrons at Mn sites have itinerant character, 2) electrons at Ni sites have localized character and 3) at Fe sites, electrons have itinerant character in the antiferromagnetic range and localized character in the ferromagnetic range. The relation between the atomic distance and the magnetic moment is discussed. The origin of the Invar effect is qualitatively explained on these bases.

Saturation Magnetization and Curie Points in Dilute Alloys of Iron

A report of the initial stages of an investigation of the intrinsic properties of dilute alloys of iron is given. Methods of determining spontaneous magnetization and Curie temperatures with precision of one part in 30 000 are discussed. The results for Fe-Ti alloys are singled out for attention. The decrease of spontaneous magnetization at a rate of more than 1.6 times that of simple dilution implies either a negative moment on the Ti atoms or more probably that the occupation of states contributing to the moment on the iron is decreased by the addition of Ti. The increase in the Curie temperature at a rate of 3.7°C per atomic percent Ti is discussed on the basis of the Bethe-Slater curve of exchange interaction as a function of atomic separation.