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The structural and magnetic characteristics of Ho2Co17−xSix (x=0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0) compounds have been investigated by means of x-ray diffraction and magnetic measurements. Powder x-ray diffractograms show that all samples are single phase and have the hexagonal Th2Ni17-type or the rhombohedral Th2Zn17-type structure. The substitution of Si for Co leads to a monotonous decrease in unit cell volume v and Curie temperature TC. The compensation points are observed for the samples with x=2.5 and 3.0, and the compensation temperatures shift to higher temperatures with increasing Si content. The intersublattice-molecular-field coefficient, nHo–Co, has been determined on the basis of magnetization curves at the compensation temperature. It has been found that the Si substitution for Co has little influence on Ho–Co exchange interaction. The magnetic phase diagram has been determined from the temperature dependence of magnetization and the XRD patterns of magnetically oriented powder samples. The...

A comparative study on magnetic and transport properties has been performed for B-site substituted perovskites La0.67Sr0.33Mn0.90B0.10O3 (B=Ga, Ni, and Fe). The doped samples show a notable decrease of the Curie Temperature, from 365 K of the undoped sample to 290 K (Ga), 292 K (Ni), and 265 K (Fe). Furthermore, the metal–semiconductor transition peaks in the doped samples shift to lower temperature, from above 300 K (undoped) to 212 K (Ga), 237 K (Ni), and 195 K (Fe). This considerable differences in magnetic and transport properties between doped and undoped samples and the diversity among the doped samples can be explained by the destruction of the partial double-exchange interactions and the exchange couplings between Mn and doped ions.

An investigation of the structure and the magnetic anisotropy of R2Co15Al2 (R=Y, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Tm) compounds has been performed by means of x-ray diffraction and magnetization measurements. X-ray diffraction shows the prepared compounds to be single phase, having the hexagonal Th2Ni17-type structure for R=Y, Ho, Er, and Tm and the rhombohedral Th2Zn17-type structure for R=Ce, Pr, Nd, Gd, Tb, and Dy. Except for the Ce compound, the unit-cell volumes of R2Co15Al2 compounds decrease in accordance with the lanthanide contraction. Substitution of Al for Co in R2Co17 leads to a decrease of the saturation magnetization at 1.5 K and Curie temperature. The exchange-coupling constants JCo–Co and JR–Co have been calculated by using the method based on magnetic ordering temperature. It is found that the JR–Co has a small dependence on the R elements and is almost not affected by the Al substitution. The Ce compound is found to exhibit an anomalous lattice parameter and magnetic characteristi...

The structure, magnetic properties and microstructure of Sm2Fe15−xCuxGa2C (x=0 and 0.5) ribbons prepared by melt spinning and subsequent heat treatment were studied. A significant increase in coercivity has been found for ribbons prepared with the addition of a small amount of Cu. The maximum coercivity μ0Hc is 1.4 and 2.0 T at room temperature for ribbons with x=0 and 0.5, respectively, after annealing in vacuum at 1043 K for 15 min. A small amount of Cu addition has little effect on the lattice parameters, Curie temperature TC, and magnetocrystalline anisotropy field HA at room temperature, while it decreases the saturation magnetization Ms. The magnetocrystalline anisotropy constants K1 and K2 for the x=0 and 0.5 samples were determined in the temperature range between 50 and 293 K, using magnetically aligned samples. The variations of coercivity, magnetization, and remanence as functions of applied field and temperature are consistent with the view that the magnetization of Sm2Fe15−xCuxGa2C ribbons wi...

The structure and magnetic properties of Pr2(Fe1−xCox)17−yGay compounds with 0⩽x⩽1 and 0⩽y⩽3 have been investigated using x-ray diffraction (XRD) and magnetization measurements. XRD patterns demonstrate that all samples were single phase with the rhombohedral Th2Zn17-type structure, except for Pr2Fe16.5Ga0.5 with some impurity phases. The replacement of (Fe, Co) by Ga results in an approximately linear increase in the unit cell volume, and decrease in the Curie temperature and saturation magnetization. The substitution of Co for Fe leads to a nonlinear variation in the unit cell volume, the Curie temperature and the saturation magnetization. The magnetic anisotropy phase diagrams of Pr2(Fe1−xCox)16.5Ga0.5 (0⩽x⩽1) and Pr2(Fe0.4Co0.6)17−yGay (0⩽y⩽3) compounds have been determined from the temperature dependence of magnetization and the XRD patterns of magnetically oriented powder samples. Most of the samples exhibit easy plane anisotropy. A small range exists in the magnetic anisotropy phase diagrams of Pr2...

X-ray diffraction (XRD) and magnetization measurements were performed to investigate the effect of Ga substitution for Co on the structural and magnetic properties of Gd2Co17−xGax compounds (x=0, 1, 2, 3, 4, 5, 6, 7, and 8). Crystal-structure studies indicate that all samples are single phase with the rhombohedral Th2Zn17-type structure except for the samples with x=7 and 8, which contain a small amount of Co. The Ga substitution for Co in Gd2Co17 compounds leads to a monotonic increase in the unit cell volume and an approximately linear decrease in the saturation magnetization. The Curie temperature TC is found to decrease monotonically from 1210 K for x=0 to 30 K for x=8. The compensation points are observed for the Gd2Co17−xGax samples with x=5 and 6. The value of the compensation temperature, determined from the temperature dependence of the magnetization measured in a magnetic field of 1000 Oe, is 120 and 152 K for x=5 and 6, respectively. It is noteworthy that the substitution of Ga for Co in the Gd...

The magnetic and transport properties of Fe doped charge ordering La0.5Ca0.5MnO3 have been studied. With the increase of the Fe ion, the ground state of the sample changes from a charge ordering state (x=0) to a spin glass state (x=0.10). The sample with x=0.04 displays a middle state, while a larger magnetoresistance of 109 at 5 K and a decrease of the critical field of charge ordering melting were found. These differences can be explained by the antiferromagnetic exchange coupling between Fe and Mn ions, the destruction of the Mn-O plane and the competition between ferromagnetic and antiferromagnetic clusters.

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.

Large magnetic-field-induced strain (MFIS) of −2700 ppm has been obtained from the Heusler alloy Ni52Mn23Ga25 at 300 K. The temperature for structure transformation was confirmed by three types of magnetic measurements. A burst of MFIS up to 5400 ppm could be induced by rotating a steady field of 1 T. In the martensitic phase, the material have a high saturated magnetization of 66 Am2/kg and a high anisotropy of 0.8 T. The variant reorientation mainly occurred in the region of 0.2–0.8 T. The large MFIS is sensitive to temperature, suggesting that it can only be induced when martensite and parent phase are coexisted.

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.

An investigation of the structure and magnetocrystalline anisotropy of Ce2Co17-xAlx (x=0, 1, 2, and 3) compounds has been performed by means of x-ray diffraction and magnetization measurements. It is observed that the unit-cell volume, Curie temperature, and saturation magnetization of Ce2Co17-xAlx compounds are anomalously low in comparison with the values obtained from a simple extrapolation by the other R2Co17-xAlx compounds, such as R=Pr and Nd. These anomalies may be an evidence of a mixed-valence behavior of the Ce ion. X-ray diffraction measurements on magnetically aligned Ce2Co17-xAlx powders with x=0-3 exhibit an easy-axis type of magnetic anisotropy at room temperature. Substitution of Al for Co leads to a change of the magnetocrystalline anisotropy of the Co sublattice from the basal plane to c axis and strongly increases the uniaxial anisotropy of Ce2Co17-xAlx. The magnetocrystalline anisotropy field H-A is found first to increase and then decrease with increasing Al concentration, attaining a maximum value of 18 kOe at x=2. The magnetocrystalline anisotropy constant K-1 shows a small decrease with increasing temperature and K-2 is almost a constant. (C) 1999 American Institute of Physics. [S0021-8979(99)56308-1].

A new multinuclear metals condensation product (polymer C) was prepared by a condensation reaction between bis(oxamide oximato)nickel and 1,1′-dicarbaldehydeferrocene. Its structure was investigated by using elemental analysis, Fourier-transform infared, x-ray diffraction, and thermogravimetric analysis techniques. All these results show that the polymer is a three-dimensional layer, large π-conjugated part order structure and its initial decomposition temperature is about 230 °C. The magnetic susceptibility was measured from 5 to 160 K by a superconducting quantum interference device magnetometer under the applied magnetic field of 10 kOe. The plot of 1/χM vs T is linear in the range of 5–30 K, but deviates from the line above 30 K. The Weiss constant θ calculated according to the equation χM=C/(T−θ) in the 5–30 K was −2.1 K, indicating presence of a weak antiferromagnetic coupling between the most near neighboring two metal ions. The polymer C can also easily complex with metal ion Cu2+, but is difficult with Mn2+.A new multinuclear metals condensation product (polymer C) was prepared by a condensation reaction between bis(oxamide oximato)nickel and 1,1′-dicarbaldehydeferrocene. Its structure was investigated by using elemental analysis, Fourier-transform infared, x-ray diffraction, and thermogravimetric analysis techniques. All these results show that the polymer is a three-dimensional layer, large π-conjugated part order structure and its initial decomposition temperature is about 230 °C. The magnetic susceptibility was measured from 5 to 160 K by a superconducting quantum interference device magnetometer under the applied magnetic field of 10 kOe. The plot of 1/χM vs T is linear in the range of 5–30 K, but deviates from the line above 30 K. The Weiss constant θ calculated according to the equation χM=C/(T−θ) in the 5–30 K was −2.1 K, indicating presence of a weak antiferromagnetic coupling between the most near neighboring two metal ions. The polymer C can also easily complex with metal ion Cu2+, but is difficul...

The temperature dependence of the electrical resistivity of amorphous (Fe1−xCox)78Si9.5B12.5 (0⩽×⩽1.0) alloys prepared by a single roller quenching apparatus was studied. The electrical resistivity of the samples was measured by using a usual four-probe method from 4.2 to 300 K. All amorphous alloys investigated here are found to exhibit a resistivity minimum at low temperature. The temperature of resistivity minimum Tmin is found first to increase and then to decrease with increasing Co content x, having a maximum value of 33.5 K at x=0.9. The electrical resistivity exhibits a logarithmic temperature dependence at T

The structure and magnetic properties of arc‐melted Gd2Fe17−xGax compounds were studied by means of x‐ray diffraction and magnetization measurements. X‐ray diffraction patterns demonstrate that all samples have a rhombohedral Th2Zn17‐type structure and the substitution of Ga leads to an approximately linear increase in the unit cell volumes. The Curie temperature is found to first increase and then decrease with increasing Ga concentration. It is noteworthy that the substitution of Ga has a significant effect on the magnetic anisotropy of iron sublattice. The easy magnetization direction of Gd2Fe17−xGax compounds changes from basal plane to c axis with increasing Ga concentration. The sample with x=7 exhibits a uniaxial anisotropy.

Amorphous Nd2(Fe1−xCox)23B3 (0≤x≤1.0) alloys were prepared by melt spinning at a speed of 47 m/s. When the amorphous samples were annealed at 900 K for 20 min, they crystallized to the metastable 2:23:3 single phase for all x. A detailed study of structure and magnetic properties of metastable Nd2(Fe1−xCox)23B3 compounds has been made by x‐ray diffraction and magnetization measurements. They are body‐centered cubic, and the lattice constant decreases linearly from a=14.16 A for x=0 to 13.86 A for x=1.0. The Fe atom moment μFe for Nd2(Fe1−xCox)23B3 was found to increase with x from 2.02μB for x=0 to 2.17μB for x=0.8, when the Co atom moment μCo is assumed to be constant, as made in previous papers for crystalline Fe–Co alloys. The Curie temperature Tc is found to increase monotonically with increasing x from 659 K for x=0 to about 1218 K for x=1.0. The thermomagnetic measurements showed that when the Nd2(Fe1−xCox)23B3 compounds were heated to certain temperatures, they decomposed to Nd2(Fe,Co)14B and α‐(...

Intermetallics compounds Dy2Fe17Cx (x=1.5,2.0,2.5,2.8) and Tb2Fe17Cx (x=1.5,2.0,2.5) have been successfully prepared by the melt‐spinning method. The x‐ray‐diffraction patterns and the thermomagnetic curves show that they are single phase with the rhombohedral Th2Zn17‐type structure, except for Dy2Fe17C2.8 and Tb2Fe17C2.5 which have a small percentage of α‐Fe. 57Fe Mossbauer spectra were measured at 12 K and room temperature to study both the magnetic properties of R2Fe17Cx on a local scale and the effect of the interstitial C atom on the Fe atoms. It is found that the effective hyperfine fields of the various Fe sites decrease in the order 6c≳18 f≳18h≳9d. The average effective hyperfine fields Heff at 12 and 293 K do not change much with C concentration x in agreement with the moment of the Fe atoms obtained by magnetic measurements at 1.5 K. It can be concluded that the effect of C is to enhance the exchange interaction between Fe‐Fe atoms, which is sensitive to the distance of Fe‐Fe atoms. The C has li...

In previous work it was discovered that the 2:17‐type rare‐earth–iron compounds with high carbon concentration could be formed by the substitution of Ga, Si, or Al, etc., for Fe in R2Fe17Cx. The effect of Al substitution for Fe on the structure and magnetic anisotropy of Sm2Fe17C has been investigated. Alloys with the composition of Sm2Fe17−xAlxC (x=2, 3, 4, 5, 6, 7, and 8) were prepared by arc melting. The carbides are single phase with rhombohedral Th2Zn17‐type structure except for Sm2Fe17C which contains a small amount of α‐Fe. The addition of Al results in an approximately linear increase in the lattice constants and the unit‐cell volumes. The Curie temperature Tc is found to increase slightly when x≤3, then decrease rapidly with increasing Al concentration, while the room‐temperature saturation magnetization decreases monotonically with the addition of aluminum. X‐ray‐diffraction and magnetization measurement studies of magnetic‐field‐oriented powders demonstrate that the samples with x≤6 exhibit an easy c‐axis anisotropy at room temperature and the room‐temperature anisotropy field increases from 5.3 T for x=0 to about 11 T for x=2. Further substitution decreases the anisotropy field. For the sample with x=2, the room‐temperature anisotropy field is higher than that of Nd2Fe14B, and the saturation magnetization is about 110 emu/g. In this alloy, the substitution of a small amount of other elements, such as Co, Ni, etc., may yield a further improvement in its magnetic properties. Thus, it is possible that these carbides can be used as the starting materials for producing high‐performance 2:17‐type sintered permanent magnets.