摘要:

The development of perpendicular anisotropy in amorphous GdCo based alloys is still not clearly understood, since no single model has been able to explain all of the various experimental results. This paper presents evidence that links the perpendicular magnetic anisotropy (Ku) in sputtered films with phase separation on a 25A˚ to 35A˚ scale as a function of bias. High resolution electron microscopy, large and small angle scattering by electrons, and Lorentz microscopy were combined in this study. Analogous to annealing E‐beam evaporated pure GdCo in UHV [Herd, J. Appl. Phys. 49, (1978) 1744], the void network is seen to disappear at −50V bias. With a drop of the compensation point below room temperature, large perpendicular domains are observed at −100V bias, comparable to the development of Ku after the glass transition in evaporated and annealed films. Further increases of bias to −200V led to a decrease in strip width to 0.25&mgr;. Application of bias in sputter deposition is seen to cause a continuous shift towards Co richer compositions, and simultaneously to effect annealing at increasing temperatures during deposition. Anisotropically shaped Co‐rich clusters are thought to be the source of perpendicular anisotropy in GdCo based alloys in general. Some recent results on peak shape in diffraction patterns and argon incorporation into sputtered films are discussed.

ISSN:0021-8979    

DOI:10.1063/1.327224

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We have investigated atomic diffusion in RF‐sputtered amorphous Gd‐Fe thin films using Auger Electron Spectroscopy (AES). Polycrystalline Co films were deposited in‐situ on amorphous Gd‐Fe films. These bilayer films were vacuum annealed to induce atomic diffusion of Co into the amorphous Gd‐Fe films. AES depth profiles were used to calculate diffusion lengths (Data)1/2where tais the annealing time, Dais the diffusion coefficient Daoexp(−Qa/KT), and Qais the activation energy. We found that Dao=10−3cm2/sec and Qa=1.3 eV suggesting that amorphous Gd‐Fe films behave like a liquid phase. Diffusion lengths of 150–250 A˚ were determined after annealing at 200–300°C for 3 hours. These results suggest that amorphous Gd‐Fe films are porous. In agreement, AES depth profiles show that amorphous Gd‐Fe films exposed to air possess an oxide surface layer 500–1000 A˚ thick. Electron diffraction studies showed that the outer halo becomes very sharp after annealing at 300°C for 3 hours. Dark‐field microscopy showed that inner halo is still due to an amorphous matrix. However, according to x‐ray microanalysis, the outer halo is associated with microcrystallization of Fe. According to our diffusion studies, such an amorphous phase separation can easily develop during sputter‐induced surface diffusion to produce perpendicular magnetic anisotropy.

ISSN:0021-8979    

DOI:10.1063/1.327225

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

A computer simulation technique has been used to study the static spin correlation in a ferromagnet with random magnetic anisotropy. An effective anisotropy constant which enables us to express the spin correlation by the domain wall equation was calculated for various values of single‐ion anisotropy constant. Allowing the spin tunnelling or not makes a significant difference in the high anisotropy region. The energy of a relaxed domain wall was calculated and it was shown that the domain wall energy approached to zero in the Ising limit, suggesting the instability of the ferromagnetic remanent state. The ground state can be obtained by creating reverse domains in the ferromagnetic state, and should be classified as the spin‐glass state. The temperature dependence of the coercivity of the amorphous magnet was explained by the theory developed for highly anisotropic crystalline magnets.

ISSN:0021-8979    

DOI:10.1063/1.327226

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Electrical resistivity (&rgr;) of glassy (FexNi100−x)80B20(x=30, 40, 50, 60, 70) has been studied as a function of temperature (T) between 300 and 1000 K using heating rates of ∼2.5 K/min. The slopes of the &rgr; vs T curves are positive for all the alloys in their glassy state. At the crystallization temperature the quantity &rgr; abruptly decreases. This decrease increases rapidly with the Fe content. No anomalies in the &rgr; vs T curves are observed at the corresponding Curie temperatures. For the sample containing 40 at.&percent;Fe, &rgr; ∼ T between 300 and 600 K. All other samples show considerable deviations from this relationship. The quantity d&rgr;/dT at 400 K increases with increasing &rgr; at 400 K for alloys with x = 40, 50, 60, and 70. The crystallization temperatures determined from the &rgr; vs T plots are in good agreement with values obtained by other techniques. A few comments are made on the nature of crystallization processes in this system.

ISSN:0021-8979    

DOI:10.1063/1.327227

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The initial permeability &mgr;iand loss factor tan&dgr; of amorphous Fe‐Co ribbons of low magnetostriction were measured at room temperature in the high frequency region from 1 kHz to 1000 kHz; the variation of &mgr;iat 10 kHz with T was also measured from room T to 300 °C. The initial permeability of as‐prepared Fe5Co73Si8B14ribbons at room T was observed to be about 600 from 1 kHz up to 500 kHz, and then to fall off. The loss factor tan&dgr; was rather small at low frequencies and increased rapidly from about 100 kHz and above. At 500 kHz, its value went up to 0.32. An irreversible T dependence of &mgr;ifrom room T to 300 °C and a disaccommodation‐like behavior of &mgr;iwith time were observed.

ISSN:0021-8979    

DOI:10.1063/1.327228

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

By rapid quenching methods, ribbon‐form Sendust alloys, silicon‐iron ribbons Fe100−xSix(4 wt&percent;<x<10 wt&percent;) in the crystalline state as well as iron‐boron and iron‐cobalt‐silicon‐boron ribbons in the amorphous state were prepared. All of the ribbons obtained were remarkably flexible. The magnetostriction constant became zero at about the composition Fe92.5Si7.5and Fe84.74Si9.71Al5.55. The coercive force Hcand the initial permeability &mgr;iin a Sendust straight ribbon with Fe84.9Si9.62Al5.48were 24 mOe and 30000 respectively after annealing. The magnetostriction constants in Fe100−xBxamorphous ribbons became larger by annealing at 300°C for 3 hours in Ar atmosphere and reached 49×10−6at x=12.

ISSN:0021-8979    

DOI:10.1063/1.327229

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We have measured, using an a.c. susceptometer, the field and temperature dependence of the magnetic response of a polymer containing chains of antiferromagnetically coupled chromium ions of ground term4A2g. The temperature dependence of the initial susceptibility indicates an exchange strength J=5.0 K. Below about 10 K, a smeared spin‐flop transition is observed centered at a field of 20 kG. The single ion anisotropy parameter, D, is thus 0.04 K. The magnitude of the spin‐flop field and the temperature below which the magnetic anisotropy exists can be reconciled in terms of a model of ordered one‐dimensional domains, separated by domain walls whose excitation energy and length are determined by J and D.

ISSN:0021-8979    

DOI:10.1063/1.327230

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Torque measurements have been made on a single crystal of MnSi to investigate the way the magnetic field‐driven transition from antiferromagnetism (AFM) to ferromagnetism (FM) is effected. The results show the transition to be more complicated than hitherto believed.

ISSN:0021-8979    

DOI:10.1063/1.327231

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Torque measurements have been performed on single crystal HoAl2compound in order to examine the origin of the 20 K specific heat anomaly that occurs in polycrystalline HoAl2. The experimental results indicate the anomaly is due to a spin reorientation between the [110] and [100] in the (100) plane as the temperature is increased. Crystal field calculations suggest the transition should be of the first order; however, torque measurements show that the transition takes place continuously over a finite temperature range.

ISSN:0021-8979    

DOI:10.1063/1.327232

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The magnetostriction (&lgr;100) and the magnetic moment of single crystal HoFe2were measured as a function of temperature down to T=4.2 K. HoFe2forms a cubic (C15) Laves phase compound with the easy axis of magnetization along the [100] crystallographic direction. At room temperature the magnetostriction is rather small with &lgr;100=−67×10−6and &lgr;111=200×10−6. &lgr;100increases substantially with decreasing temperature reaching a value of −745×10−6at T=4.2 K. This behavior is contrary to that observed in DyFe2(also [100] easy) where &lgr;111≫&lgr;100. The decrease in &lgr;100with increasing temperature was found to be much more rapid than could be explained by lowest order single‐ion magnetoelastic theory. On the other hand, magnetostriction measurements of &lgr;111over the temperature range 275–325 K result in a temperature dependence which can satisfactorily be explained by the single‐ion model. The spontaneous magnetic moment at T=0 K is 134.5 emu/g. Taking the the gJ value of 10 &mgr;bfor the Ho3+sublattice moment results in an Fe moment of 1.67 &mgr;b. This value is nearly equal to those previously obtained in other RFe2compounds. The magnetization curves at room temperature along the principal crystallographic directions yield anisotropy constants K1=5.5×106erg/cm3and K2=6.4×106erg/cm3.

ISSN:0021-8979    

DOI:10.1063/1.327233

出版商:AIP    

年代:1979

数据来源: AIP