Temperature Dependence Of Anisotropy Field Research Articles

Phase precipitation and properties of melt-spun Ho-Fe-B alloys prepared by direct quenching and over-quenching followed by heat treatment

Aiming to fully utilize rare earth (RE) resources and develop new high coercivity magnets, the magnetic properties and phase precipitation behavior of Ho-Fe-B alloys were systematically studied. The Ho12+xFe82-xB6 (x = −2, −1, 0, 1, 2) alloys were prepared by melt spinning at various wheel speeds. For the directly quenched Ho12Fe82B6 alloy, the optimum magnetic properties can be obtained at a wheel speed of 22 m/s with the coercivity Hcj = 1.07 × 103 kA/m, remanence Jr = 0.45 T and maximum energy product (BH)max = 36.6 kJ/m3 due to its single Ho2Fe14B phase structure. A maximum Hcj = 2.95 × 103 kA/m can also be obtained at 100 K due to the temperature dependence of anisotropy field and existence of spin reorientation of Ho2Fe14B compound. Jr decreases with decreasing temperature owing to the antiparallel coupling between Ho and Fe moments. The increase of Ho content can enhance the coercivity but deteriorate the remanence. More than 2 at. % reduction of Ho leads to the formation of soft magnetic Ho2Fe17 phase and greatly reduces the coercivity, which is different from many other RE-Fe-B alloys. The phase precipitation behavior of over-quenched amorphous Ho12+xFe82-xB6 alloys during heat treatment were also studied, and the precipitation of Ho2Fe14B phase is confirmed in all alloys. Ho2Fe17 phase precipitates in the Ho10Fe84B6 alloy at the temperature of 882.7 K. The magnetic properties of over-quenched Ho12+xFe82-xB6 alloys after optimally annealed are similar to the directly quenched alloys. In addition, the corrosion resistance of the directly quenched alloys was also investigated. The present results provide reference for developing highly stable RE-Fe-B based magnets with alternative RE resource.

Measuring Temperature Dependence of Anisotropy Field in Heat-Assisted Magnetic Recording Media by Pump–Probe Method

Temperature dependence of medium anisotropy field is an important property for recording performance in heat-assisted magnetic recording. In this paper, we report a pump–probe technique to characterize the temperature dependence of the anisotropy field. An experimental measurement is performed on two prototype FePt $L1_{0}$ -based recording media samples, which shows different temperature dependences of anisotropy field. Micromagnetic modeling study validates and provides further understanding of this technique. The simulation result shows the excellent agreement of an obtained value with actual medium property, especially near Curie temperature.

Microstructure and temperature dependent of coercivity of hot-deformed Nd–Fe–B magnets diffusion processed with Pr–Cu alloy

The coercivity of hot-deformed Nd–Fe–B magnet was substantially enhanced from 1.0T to 2.6T by the grain boundary diffusion process using Pr–Cu alloy. However, the temperature dependence of coercivity is larger compared to the sample diffusion processed with Nd–Cu. Microstructure studies showed a good isolation of platelet shaped Nd2Fe14B grains by Pr-rich intergranular phase, which explains pronounced coercivity at room temperature. Small portions of Nd2Fe14B become (Nd,Pr)2Fe14B phase, which has a higher anisotropy field compared to that of the Nd2Fe14B phase at room temperature, while it becomes lower than that of the Nd2Fe14B phase above ∼110°C. Co is depleted from the (Nd,Pr)2Fe14B phase, which is considered to cause a slight decrease in Curie temperature. Micromagnetic simulations with the magnetically isolated grains including (Nd,Pr)2Fe14B regions showed that the degradation of thermal stability of coercivity in the Pr–Cu diffusion processed sample is due to the large temperature dependence of anisotropy field in the (Nd,Pr)2Fe14B regions.

Temperature dependence of anisotropy field in Co-Ti substituted Ba-ferrite particles

Co-Ti substituted Ba-ferrite particles were prepared, and the crystalline and shape anisotropy energies were measured in the temperature range of 78 K to 400 K to determine the crystalline anisotropy field of the particles. The crystalline anisotropy energy and the crystalline anisotropy field at room temperature were about 0.67*10/sup 6/ erg/cm/sup 3/ and about 4700 Oe, respectively. A similar temperature dependence was observed between the effective anisotropy field and the coercivity. This and a high intrinsic coercivity indicate coherent rotation of the magnetic moment in single-domain particles. >

Effect of Ga and Nb addition on the magnetic properties of the Nd 2(Fe, Co) 14B compound

The Curie temperature, saturation magnetization and ac-susceptibility of Nd 2Fe 11.5- x-y Co 2.5Ga x Nb y B compounds in the concentration range O⩽ x⩽0.2 and O⩽ y⩽0.3 are determined. The Curie temperature of the compounds lying in the single phase region is approximately 480°C irrespective of the variation of Ga(Nb) content. Both room temperature saturation magnetization and spin reorientation temperature determined by ac-susceptibility measurements between 70 and 300 K were found to decrease with increasing Ga(Nb) concentration. Room temperature anisotropy field of single phase Nd 2Fe 11.5- x-y Co 2.5Ga x Nb y B decreases with increasing Nb content when Ga is kept constant, whereas when the Nb-content is constant it increases first with increasing Ga, and decreases again after reaching a maximum. The results of temperature dependence of anisotropy field of Nd 2Fe 11.5- x-y Co 2.5Ga x Nb y B series show that the effect of addition of Ga(Nb) on the anisotropy field is different in different temperature ranges. It is thought that different Fe crystallographic sites of the 3d- sublattice of Nd 2Fe 14B type structure may contribute differently to the anisotropy field and that the temperature dependence of the anisotropy field indicates that the contribution to anisotropy field from a specific Fe site is different at different temperatures.

Variations in temperature coefficient of anisotropy and coercivity in finite particles of Nd/sub 2/Fe/sub 14/B type recording materials through substitutions

A theoretical and experimental study is reported on how to modify the temperature dependence of coercivity, H/sub c/(T), in R/sub 2/F/sub 14/B type compounds (R=rare earth) through modifications of the temperature dependence of anisotropy field, H/sub A/(T). This is accomplished by partial substitutions on R sites. Experimentally it is found that for Y/sub 2/Fe/sub 14/B fine particles ( approximately 1- mu m), values of H/sub c/ are in the range of 1 kOe. For these materials, a slightly positive H/sub c/(T) is obtained near 300 K. Stable H/sub A/(T) and H/sub C/(T) near 300 K are obtained, e.g., with Nd/sub 0.2/Y/sub 0.8/Fe/sub 14/B, while strongly increasing H/sub A/(T) and H/sub c/(T) are obtained with small substitutions of Er for Y in Y/sub 2/Fe/sub 14/B. More complex H/sub A/(T) and H/sub c/(T) can be obtained in more complex systems.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Ｎｄ２Ｆｅ１４Ｂ型化合物の磁性とＮｄ‐Ｆｅ‐Ｂ磁石の特性

Temperature dependence of anisotropy field (HA) and spontaneous magnetization (Is) of Nd2Fe14B-type compounds in which Nd or Fe atoms are partially substituted by one of Dy, Co and Al is reported in connection with temperature dependence of intrinsic coercivity (HcI) of sintered Nd-Fe-B-type magnets containing the substituents at the same ratio as in the investigated compounds. Results are discussed in the light of empirical relation among HcI, HA and IS; μ0HcI=μ0HA-IS. Dy is recognized as an indispensible additive that improves the thermal stability of the magnetic properties of the Nd-Fe-B-type magnets, whereas Co, which improves temperature coefficient of remanent induction through a marked increase in the Curie temperature, has no possibility of bringing forth an increased thermal stability.

Temperature dependence of anisotropy fields and initial susceptibilities in R 2Fe 14B compounds

The temperature dependence of the anisotropy field was determined in various R 2Fe 14B compounds (R = Y, La, Ce, Pr, Nd, Gd, Ho, Lu and Th). The magneto-crystalline anisotropy in materials where the R component has an orbital moment consists of two different contributions that have an opposite temperature dependence. At temperatures well below the Curie temperature the 4f sublattice anisotropy decreases with temperature while the 3d lattice anisotropy increases with temperature. We measured the temperature dependence of the initial susceptibility of all R 2Fe 14B compounds mentioned, including the compounds with R = Sm, Dy, Er and Tm in the range from 4.2 to 300 K. Indications for the presence of a spin reorientation were found in Pr 2Fe 14B, Nd 2Fe 14B and Ho 2Fe 14B.

Spin reorientation in the low temperature phase of KMnF 3

The temperature dependence of anisotropy fields of the canted antiferromagnet KMnF 3 at the low temperature phase has been investigated by analysing the antiferromagnetic resonance. The results show that there exists a second-order magnetic transition associated with the spin reorientation at T 0 ∼ 50°K in the absence of applied fields.