Showing papers in "IEEE Transactions on Magnetics in 1986"
TL;DR: In this paper, a permanent magnet motor with power semiconductor supply and shaft position sensing can be constructed using radially-directed high energy magnets on its rotor, and equivalent circuit models for such motors are presented.
Abstract: A permanent magnet motor with power semiconductor supply and shaft position sensing can be constructed using radially- directed high energy magnets on its rotor. This paper presents equivalent circuit models for such motors. The model parameters are related to the motor structure and dimensions. Computed values of parameters are compared with those measured from two experimental motors with different rotor construction.
155 citations
TL;DR: In this paper, a method for setting up system equations and the control design problem for a horizontal-shaft-type magnetic bearing system is discussed, and the fundamental equations of the motion of the rotor by adapting the dynamic theory of flight problems to this system are obtained with gap-length displacements and controlled currents taken as the state variables.
Abstract: A method for setting up system equations and the control design problem for a horizontal-shaft-type magnetic-bearing system are discussed We obtain the fundamental equations of the motion of the rotor by adapting the dynamic theory of flight problems to this system and then obtain the system equations with gap-length displacements and controlled currents taken as the state variables By constructing an integral-type control system, we are able to maintain the rotor in the center position in the final steady state
119 citations
TL;DR: In this paper, a mean-field model for amorphous ferromagnetic materials with potential applications in thermomagnetic recording/magneto-optical readout systems is developed.
Abstract: A mean-field model is developed for amorphous ferromagnetic materials with potential applications in thermomagnetic recording/magneto-optical readout systems. The emphasis is on the reduction of the number of adjustable parameters, so that important variables and their effects on magnetic properties can be investigated. The available experimental data on GdCo-, GdFe-, and TbFe-based alloys is compared with the model predictions and good agreement is obtained in all cases. Expressions for the exchange stiffness coefficient and macroscopic anisotropy energy constant are derived and the latter is compared with available experimental data. The results have been used to study domain wall characteristics of the three material systems.
108 citations
IBM1
TL;DR: In this paper, the magnetooptic Kerr effect was employed for imaging magnetic domains with spatial resolution of less than 0.5 µm, which is applicable for observing surface domain structures, even if the magnetic surface of interest is covered by a thick transparent overcoat.
Abstract: A method for imaging magnetic domains with spatial resolution of less than 0.5 µm is described. The method employs the magnetooptic Kerr effect and is applicable for observing surface domain structures, even if the magnetic surface of interest is covered by a thick transparent overcoat. Polarized laser light, incident at an oblique angle, is focused to a diffraction limited spot onto a surface whose magnetization is modulated at a fixed frequency by a magnetic field. The modulation in the polarization of the light due to the modulation of the magnetization beneath the spot is measured with the use of a lock-in amplifier. An image of the magnetization changes is then constructed by scanning the spot. Domains are revealed because areas of domain wall motion have larger magnetization changes than areas of magnetization rotation within domains. Since this approach minimizes noise and eliminates nonmagnetic signals, the domain image contrast is greatly enhanced. With 0.3 mW of laser power on a spot and a detection bandwidth of 10 Hz, signal to noise ratios of 65 db and a magnetization rotation sensitivity of 0.06° have been obtained in permalloy. Results of domain images in thin-film inductive heads are presented. This technique is ideally suited for the study of the dynamics of wall motion and magnetization rotation in magnetic films.
101 citations
IBM1
TL;DR: In this paper, a noise model based on the micromagnetics of film domains is proposed to characterize the nature of the zigzags and the noise behavior associated with them.
Abstract: Lorentz microscopy images of recorded bit patterns on a metal film disk are used to demonstrate that even though the magnetization transitions are zigzag domain walls, the effective transition profile for a sufficiently wide track resembles an error function, rather than an arctangent. However, the Williams-Comstock arctangent model accurately predicts the slope of the transition. Digitized Lorentz-image zigzags, as well as the Lorentz images themselves, can be used to characterize the nature of the zigzags and the noise behavior associated with them. A proposed noise model based on the micromagnetics of film domains is included here.
91 citations
TL;DR: In this article, the magnetic properties, recording performance and corrosion resistance of sputtered CoCr alloy films and CoCrTa alloy films were described and compared for a two-week period equivalent to at least six years under ambient disc drive conditions.
Abstract: This paper describes the magnetic properties, recording performance and corrosion resistance of sputtered CoCr alloy films and CoCrTa alloy films. The saturation magnetization of CoCr was 525 emu/cc and not affected by substitution of a small amount of Ta. CoCrTa films exhibit greater coercive force values than CoCr films. The maximum coercive force of CoCrTa was 1400 Oe at a thickness of 400A, whereas at a similar thickness the coercive force of CoCr was 900 Oe. The coercive force decreases linearly with temperature (25°C. to 125°C.) at a rate of 3.16 Oe/°C. for CoCrTa and 1.87 Oe/°C. for CoCr. Longitudinal recording performance at -3 dB signal level was 8386 flux reversals/cm (21,300 fci) and 11,063 flux reversals/cm (28,100 fci) for CoCr and CoCrTa respectively. The alloys exhibited corrosion resistance at 80% relative humidity and 65° C. for a two-week period equivalent to at least six years under ambient disc drive conditions.
88 citations
TL;DR: The theory of magnetization reversal process in an isolated, ellipsoidal particle is rigorous and its results are unambiguous as discussed by the authors, except for the assumption of a perfect single crystal, with a perfectly smooth spheroidal surface.
Abstract: The theory of magnetization reversal process in an isolated, ellipsoidal particle is rigorous, and its results are unambiguous. There is no approximation in this theory, except for the assumption of a perfect single crystal, with a perfectly smooth spheroidal surface, and nothing new can be found, as long as this assumption is maintained. In order to advance towards a theory of realistic particles, one must look for ways to take into account the effect of nonellipsoidal shape and of crystalline defects, as well as the effect of magnetic interactions between the particles.
87 citations
TL;DR: In this paper, a simple one dimensional thermal model with the vapor jet considered as a transient heat flux onto the electrode surface led to a figure of merit for the electrode materials which was in close agreement with experiments.
Abstract: Electrode erosion in high current, high energy spark gaps was examined both theoretically and experimentally. A brief description is given of the production of high velocity, high temperature electrode vapor jets which are shown experimentally to be the major source of electrode erosion under these conditions. Consideration of a simple one dimensional thermal model with the vapor jet considered as a transient heat flux onto the electrode surface led to a figure of merit for the electrode materials which was in close agreement with experiments. The rapid decrease in erosion with increasing gap separation was also measured and explained by the vapor jet mechanism. Erosion rates are given for a large number of electrode materials including many copper composites, such as copper niobium and copper tungsten. Possible implications of these results on rail gun design are also given.
79 citations
TL;DR: In this paper, a magnetoplumbite type of hexagonal Ba-ferrite films, whose c-axis of crystallites is well oriented perpendicularly to the film plane, have been prepared by means of a conventional rf diode sputtering system.
Abstract: A magnetoplumbite type of hexagonal Ba-ferrite films, whose c-axis of crystallites is well oriented perpendicularly to the film plane, have been prepared by means of a conventional rf diode sputtering system. Morphological and crystallographic characteristics of sputtered Ba-ferrite films depend strongly on preparation conditions such as the distance between target and substrate d T-S and partial pressure of oxygen gas P O2 during the deposition. Ba-ferrite films with smooth surface are prepared at the extended d T-S in the region of low P O2 . Read/write characteristics of Ba-ferrite thin film deposited on thermally oxidized silicon wafer with radius of two inches were evaluated with ring type head. Recording density D 50 of Ba-ferrite thin film rigid disk depends strongly on Δθ 50 . In this work, D 50 of 110 and 190 kfrpi for Δθ 50 of 4.8 and 2.8°, respectively, have been attained.
74 citations
TL;DR: In this article, the reverse DC erase noise of thin metal film media was investigated using a new method: the reverse dc erase media noise measuring method, which showed a sharp peak at the field around coercive force Hc.
Abstract: The noise of longitudinal thin metal film media is experimentally investigated using a new method: the reverse DC erase media noise measuring method. The reverse DC erase noise of thin metal film shows a sharp peak at the field around coercive force Hc. The maximum reverse DC erase noise has a strong correlation to the signal recorded noise. Media with large noise has low D 50 and also low Overwrite S/N.
73 citations
TL;DR: In this article, a large part of the nonlinear distortion introduced in the recording process can be modelled as a shift in the effective position of the recorded transitions, which can explain the distinctive distortion evident in Class IV partial-response eye-patterns reproduced from a magnetic recording channel.
Abstract: A large part of the nonlinear distortion introduced in the recording process can be modelled as a shift in the effective position of the recorded transitions, it is shown that such transition shifts can explain the distinctive distortion evident in Class IV partial-response eye-patterns reproduced from a magnetic recording channel.
TL;DR: The easy axis of magnetization was perpendicular to the film plane which correlated with a preferential texturing of the c-axis out of the film planes as observed by x-ray diffraction.
Abstract: Film samples of Nd 2 Fe 14 B which exhibit perpendicular anisotropy have been synthesized by selectively thermalized sputtering onto heated substrates. Minor hysteresis loops measured with fields up to 20 kOe perpendicular to the film plane exhibited a remanent moment of 9.3 kG and an intrinsic coercive force, i H c , of 14.8 kOe at room temperature. The easy axis of magnetization was perpendicular to the film plane which correlated with a preferential texturing of the c-axis out of the film plane as observed by x-ray diffraction. Effective large perpendicular anisotropy constants of 1.2 × 107erg/cc have been observed. Films sputtered at deposition rates lower than 1.8 A/sec exhibited perpendicular anisotropy while those deposited at rates greater than this exhibited in the plane anisotropy.
TL;DR: In this article, a method for analyzing the magnetic field in a capacitor-discharge impulse magnetizer is established by modifying the finite element method and the effects of charging voltage, capacitance and resistance on the behavior of localized fluxes in the Impulse magnetizer are analyzed quantitatively.
Abstract: A method for analyzing the magnetic field in a capacitor-discharge impulse magnetizer is established by modifying the finite element method. The effects of charging voltage, capacitance and resistance on the behaviour of the localized fluxes in the Impulse magnetizer are analyzed quantitatively. As the detailed distribution of the flux density can be obtained, the optimum design of the magnetizer which produce desired magnet will be possible using our new method.
TL;DR: The information density improvements are estimated that are feasible by applying decision feedback equalization instead of conventional linear equalization in digital magnetic recording systems, with differentiating playback heads.
Abstract: The information density improvements are estimated that are feasible by applying decision feedback equalization instead of conventional linear equalization in digital magnetic recording systems, with differentiating playback heads. Significant improvements are shown to be within reach for an important class of transmission codes.
TL;DR: In this article, a model for the inversion of eddy-current data to be used for the detection of flaws is presented, based on rigorous electromagnetic theory and uses a multifrequency approach to make it truly three-dimensional.
Abstract: A model is presented for the inversion of eddy-current data to be used for the detection of flaws. This model is based on rigorous electromagnetic theory and uses a multifrequency approach to make it truly three-dimensional. The resulting integral equations are discretized and solved using least squares techniques. The numerical problems involved in this algorithm are discussed, and a solution as well as examples of reconstructions of computer-generated flaws are presented.
TL;DR: In this article, permanent magnet structures that produce helical transverse magnetic fields of 0.5 to 2.0 kOe in circularly polarized microwave/millimeter-wave sources are discussed and compared with respect to performance, economy, ease of manufacture, and general utility.
Abstract: A need has arisen for permanent-magnet structures that produce helical transverse magnetic fields of 0.5 to 2.0 kOe in circularly polarized microwave/millimeter-wave sources. Three such configurations are discussed and compared with respect to performance, economy, ease of manufacture, and general utility.
TL;DR: In this paper, the authors used a helium gas-driven injector and railgun launcher to accelerate 1-and 4-g polycarbonate projectiles intact up to 6.6 and 3.0 km/s, respectively.
Abstract: Performance results for three railguns are summarized. The system used a helium gas-driven injector and railgun launcher to accelerate 1- and 4-g polycarbonate projectiles intact up to 6.6 and 3.0 km/s, respectively. A 625 kJ capacitor bank powered the railgun, and an adjustable inductor provided pulse shaping and peak current control. Operation in hard and soft vacuum was reliably achieved. Projectiles were accelerated without blowby of injector gas or plasma. The diagnostic system measured the projectile position and launch velocity, verified that the projectile was launched intact in the desired direction, and identified system components where improvements could enhance performance. Flash x-ray radiography measured velocity and verified that projectiles were intact. Post-launch projectile travel along the axis of the launcher without tilt was recorded with flash radiographs and impact impressions or holes in witness plates. The system performed as expected up to 4-5 km/s but below expectations at higher velocities. Our diagnostics suggest that the decreased performance was probably caused by the restriking of a second arc in the breech of the railgun, which shunted the current from the propulsive arc. Estimates of ablated launcher mass, drag forces, methods of eliminating restrike, and suggestions for improving the performance of railguns are discussed.
TL;DR: In this article, the effect of grain size on core loss and permeability was studied in three heats of silicon-free motor lamination steel, and the results showed that at the commercially important induction of 15 kG, the core loss decreased and the permeability increased as the grain size increased from 7 to 90-160 µm.
Abstract: The effect of grain size on core loss and permeability was studied in three heats of silicon-free motor lamination steel. Grain sizes in the final test specimens ranged from 7 to 1360 µm. The core loss and permeability were measured at 10 and 15 kG ac, and 15 kG dc. Regression equations were constructed which took account of the effects of major changes in grain size as well as of minor variations in thickness, resistivity, texture, and inclusions on core loss and permeability. At the commercially important induction of 15 kG, the ac core loss decreased and the permeability increased as the grain size increased from 7 to 90-160 µm. As the grain size increased further, the core loss increased gradually and the permeability decreased sharply. Similar results were obtained at 10 kG ac and 15 kG dc.
TL;DR: The magnetostrictive properties of cubic Laves phase Tb 0.27 Dy 0.73 Fe 2 prepared by Czochralski and a free standing r.f. zone method, were examined as mentioned in this paper.
Abstract: The magnetostrictive properties of cubic Laves phase Tb 0.27 Dy 0.73 Fe 2 prepared by (a) Czochralski and (b) a free standing r.f. zone method, were examined. Crystals were found to grow preferentially along [ 11\bar{2} ] in twinned dendrite sheets with [111] normal. The saturation magnetostriction along [111] is very large ( \lambda_{111} = 1640 \times 10^{-6} ), in excellent agreement with that of single crystal Tb .27 Dy .73 Fe 2 . The magnetostriction along [ 11\bar{2} ] is larger than expected. For magnetic fields less than 2000 Oe, the magnetostriction is much smaller, presumably due to internal energy stored at the twin boundaries.
TL;DR: In this paper, anisotropy induced signal waveform modulation was observed through the use of a disk certifier and verified with vibrating sample magnetometer (VSM) orientation measurements and electron microscopic observation of grain structure.
Abstract: Thin films of Co-alloy, intended for use in longitudinal recording, were deposited onto variously prepared substrates by in-line DC magnetron sputtering. An anisotropy induced signal waveform modulation was observed through the use of a disk certifier and verified with vibrating sample magnetometer (VSM) orientation measurements and electron microscopic observation of grain structure. The partial low angle of incidence which can occur in in-line sputtering, the magnetic field generated from the magnetron target, the surface topography of substrates and the sputtering conditions, all affected the extent of preferred anisotropy in the films. By minimizing low angle of incidence sputtering, texturing the substrate surface circumferentially, and adjusting the processing conditions, we can eliminate not only the signal waveform modulation but also enhance the magnetic properties.
TL;DR: In this paper, the determination of electromagnetic fields in permanent magnet linear synchronous machines (PMLSMs) is discussed, which form the basis for the evaluation of forces and parameters of PMLSM'S.
Abstract: The determination of electromagnetic fields in permanent magnet linear synchronous machines (PMLSM's) to form the basis for the evaluation of forces and parameters of PMLSM'S (to be presented in a subsequent paper) is discussed. Analytical techniques applied to permanent magnet rotary synchronous machines are modified and adapted to PMLSM's. Fields are determined analytically in a single-sided PMLSM, and computed results by the finite-element method are compared with those obtained experimentally. A good correlation between the results obtained by the three procedures-analytical, finite-element computational, and experimental-validates the approximations used in the analysis.
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TL;DR: The reconnection gun as mentioned in this paper was proposed to produce higher acceleration with a lower energy loss to ohmic heating, and it has several advantages for producing higher acceleration including; no barrel, no drop in acceleration with increase in projectile mass, higher peak pressure on the projectile and smaller differences between average and peak pressure.
Abstract: An electromagnetic launcher called the reconnection gun is introduced. Its potential performance is shown to be superior to that of a modern railgun for projectiles with mass greater than a few hundred grams. It has a "characteristic velocity" which is an order of magnitude lower for much lower energy loss to ohmic heating. Also, it has several advantages for producing higher acceleration including; no barrel, no drop in acceleration with increase in projectile mass, higher peak pressure on the projectile and smaller differences between average and peak pressure. Experimental results and plans for high-performance, multi-stage designs are briefly discussed.
TL;DR: In this paper, the performance of a single-sided linear induction motor (SLIM) with a double-layer reaction rail, under constant current excitation, is presented. But it does not take into account the reaction of secondary eddy currents on the airgap field, transverse edge and longitudinal end effects, together with skin effect, saturation, nonlinear magnetic permeability, and hysteresis in the solid steel core of a reaction rail.
Abstract: A method for computing the performance of a single-sided linear induction motor (SLIM) with a double-layer reaction rail, under constant current excitation, is presented. This method takes into account the reaction of secondary eddy currents on the airgap field, transverse edge and longitudinal end effects, together with skin effect, saturation, nonlinear magnetic permeability, and hysteresis in the solid steel core of a reaction rail. In an equivalent circuit of the machine, the mutual and secondary impedances are found from a solution of the two-dimensional electromagnetic field distribution. Modifying factors account for configurations in which the width of the secondary conductive layer is different from that of the steel core, and in which the thickness of the conductive overhand is different from that over the steel core. Good correlation is obtained between analysis and test results from a large-scale linear induction motor (LIM) at Queen's University. The developed expressions are appropriate for small and large LIM's and may also be used for constant voltage excitation conditions.
IBM1
TL;DR: In this article, the authors have developed novel piezoelectric techniques for monitoring contacts and mechanical resonances in the head-disk assembly, allowing use at the component level or in a fully assembled unit.
Abstract: As the flying heights of air bearing sliders are reduced to improve magnetic recording linear density, mechanical tolerances on the head-disk interface become more critical and real time measurement of wear-out phenomena becomes essential. We have developed novel piezoelectric techniques for monitoring contacts and mechanical resonances in the head-disk assembly. The techniques are real time and nondestructive, allowing use at the component level or in a fully assembled unit. Two sensor types will be described and data will be given for tests in which these sensors have been used to monitor flexure and suspension resonances, air bearing resonances, head-disk contacts, and disk roughness.
TL;DR: In this paper, three areas of current interest in particulate recording media are examined: the reversal modes in recording particles, whether the classical coherent and incoherent modes are more appropriate than that of heterogeneous nucleation and growth of regions of reversed magnetization.
Abstract: Three areas of current interest in particulate recording media are examined. The first concerns the reversal modes in recording particles-in particular whether the classical coherent and incoherent modes are more appropriate than that of heterogeneous nucleation and growth of regions of reversed magnetization. Secondly, magnetization relaxation is considered, with emphasis on its role in defining the observed coercivity. Finally, the effects of coating particles are discussed, especially the epitaxial Co-coated materials.
TL;DR: In this article, the effects of magnetic fields on combustion of alcohol and hydrocarbons are studied to simulate in part the oxidation of organic matter in the living body, and no clear positive effects are observed in experiments of biochemical reactions and embryogenesis under magnetic fields of the same intensities.
Abstract: The effects of magnetic fields on biological and chemical processes are investigated. Time-varying magnetic fields produce eddy currents which stimulate excitable tissues at low frequencies and give rise to thermal effects at high frequencies. Biological and chemical effects of static magnetic fields are poorly understood. The effects of magnetic fields on combustion of alcohol and hydrocarbons are studied to simulate in part the oxidation of organic matter in the living body. The combustion temperature of alcohol with platinum catalysis decreases rapidly within a range 100-200°C when the place of combustion reaction is exposed to gradient magnetic fields (0.5-1.4T, 20- 200 T/m). To explain this phenomenon, an experiment is demonstrated where candle flames are exposed to gradient magnetic fields. The flames bend so as to escape from magnetic fields of higher intensities. The study is focused on the role of oxygen as a paramagnetic molecule and on the behavior of charged particles in magnetic fields. In contrast with the combustion experiments, no clear positive effects are observed in experiments of biochemical reactions and embryogenesis under magnetic fields of the same intensities.
TL;DR: In this article, a recording density of 50 KBPI was achieved for a diamagnetic alumite disc with a media thickness of 1.5 µm and a recording characteristics of 3.5 and 5.25 inch rigid discs were evaluated.
Abstract: Perpendicular magnetic alumite discs were obtained using an anodic oxidation method.The additional new pore widening process was effective to control the coercive force. The electro-deposited fine iron needles were single crystals and the growth direction was [110]. The recording characteristics of 3.5 and 5.25 inch rigid discs were evaluated. A recording density D 50 of 50 KBPI was attained for the disc with a media thickness 1.5 µm. The environmental test under an atmosphere of of 40 °C 90 % R. H. over 1000 hr affirmed the stability of the alumite disc with 250A SiO 2 overcoat.
TL;DR: In this article, the authors studied the origin of the high coercive force of sputtered CoNiCr/Cr film and showed that the CoNiC/Cr has a fine grain structure with magneto-crystalline anisotropy oriented in the plane, which results in a high coercive forces in the film plane.
Abstract: The origin of the high coercive force of sputtered CoNiCr/Cr film was studied and it has been shown that the CoNiCr/Cr film has a fine grain structure with magneto-crystalline anisotropy oriented in the plane, which results in a high coercive force in the film plane. The addition of Ni to Co magnetic layer increases both the magneto-crystalline anisotropy and the coercive force. From the temperature dependence of the saturation magnetization, on depositing the Cr contained alloy films by sputtering, Cr segregates near the grain boundaries and enhances the magnetic isolation of grains, which increases the coercive force.
TL;DR: In this article, a detailed and practical chip organization of Bloch line memory is proposed on the basis of preliminary experiments and computer simulations, where the major line - minor loop organization is composed of two levels zigzag conductors to propagate bubbles (major line) and stripe domain walls surrounding the epitaxial garnet layer.
Abstract: A detailed and practical chip organization of Bloch line memory is proposed on the basis of preliminary experiments and computer simulations. The major line - minor loop organization is composed of two levels zigzag conductors to propagate bubbles (major line) and stripe domain walls surrounding grooved region where the epitaxial garnet layer is completely etched (minor loops). The garnet film thickness is chosen as one half of the usual bubble memory chip, which reduces the magneto-static attractive force between bubbles and between Bloch line pairs, and is preferable for Bloch line potential well generation to define bit position. New practical methods for VBL read-write operation are established by simulations and experiments.
TL;DR: In this paper, the microstructure including grain boundaries of (Nd0.86Dy0.14) (Fe0.92B0.08)z sintered magnets was studied using FE-SEM, AES and TEM.
Abstract: The microstructure including grain boundaries of (Nd0.86Dy0.14)(Fe0.92B0.08)z sintered magnets was studied using FE-SEM, AES and TEM. It is revealed that there is a composition fluctuation in the R rich phase, and that there is a BCC phase with a = 0.29nm which is coherent with the R 2 Fe 14 B matrix between the R rich phase and the matrix. The change of iHc and the microstructure with composition and heat treatment for(Nd0.86Dy0.14) (Fe0.92B0.08)z sintered magnets(z=4.0, 5.0, 5.4 and 6.2) was investigated, iHc increased as the z-value decreased from 6.2 to 4.0. The width of the BCC phase which surrounds R 2 Fe 14 B grains has a tendency to become greater with decreasing z-value from z=5.4 to 4.0. No BCC phase was observed for z=6.2, where iHc was only 200 Oe. There were many BCC platelets in specimens with z=4.0, 5.0 and 5.4 which had been heat treated at 900°C for two hours and cooled gradually to room temperature. After a final heat treatment near 600°c, the BCC platelets disappeared, except for z=5. The substitution of Co for Fe in the alloy (Nd0.8Dy0.2)(Fe0.92-xCoxB0.08)5.5 was studied in the range x=0 to 0.10. An irreversible loss of under 5% after exposure at 200°C (Pc=2) was obtained with x=0.06 and Tc=380°C. For the alloy with x=0.06, the irreversible loss was found to depend on the final heat treating temperature, T 2 . A specimen heat treated for one hour at 600°C and water quenched showed the lowest irreversible loss. The Tc of the BCC phase for T 2 =600°c was 330°C and the higher Tc of the BCC phase is required to have higher thermal stabilities.