Magnetic Properties of Amorphous Fe_90.6Zr_9.4

Abstract

The temperature dependence of the spontaneous magnetization, M,, and the magnetization curve of melt-spun amorphous Fego.6Zrg.a alloys are investigated by means of a SQUID magnetometer in the temperature range 4.2 K < T < 150 K, and for magnetic fields 1 mT < poH < 4 T. At low magnetic fields, poH < 80 mT, M , is found to obey a F l a w whereas for poH > 0.27 T Bloch's TW-law is obtained. No evidence for a spin-glass transition a t low temperatures can be detected. The high-field susceptibility points to the presence of circular quasidislocation loops.Die Temperaturabhiingigkeit der spontanen Magnetisierung, M,, und der Magnetisierungskurve schnell abgeschreckter amorpher Feg0,6Zr9,4 Legierungen werden mit Hilfe eines Squidmagnetometers im Temperaturbereich 4,2 K < T < 150 K und fur magnetische Felder 1 mT < p,,H < < 4 T untersucht. Bei kleinen Magnetfeldern < 80 mT ergibt sich fur M , ein T2-Gesetz, wahrend fur poH > 0,27 T das Blochsche T312-Gesetz gefunden wird. Fur einen Spinglasubergang bei tiefen Temperaturen konnen keine Hinweise gefunden werden. Die Hochfeldsuszeptibilitat weist auf die Existenz kreisformiger Quasiversetzungsringe hin.

Low-lying magnetic excitations in amorphous and alloys

“…The last term in equation ( 23) is normally too small to merit consideration because the coefficient B usually has a value close to zero (note that depending upon the structure of the DOS curve and hence on the relative magnitude of its derivatives, B can be either positive, negative or zero) but it can be significant for systems in which S has an extremely large value, i.e., for very weak itinerant ferromagnets in which I N(E F ) → 1 and hence S → ∞. From the coefficient of the T 2 -term in equation (23), it is evident that LSF (Stoner SP excitations) dominantly contribute to M(T , 0) if T 0 T S C (T S C T 0 ). However, if T 0 ≈ T S C , the contributions due to LSF and SP excitations are comparable in magnitude.…”

“…However, if T 0 ≈ T S C , the contributions due to LSF and SP excitations are comparable in magnitude. Recognizing that equation (23) can be put into the form [M(T , 0)/M(0, 0)] 2 = 1 − 2AT 2 + A 2 T 4 , equation (23) can be generalized to…”

“…In this picture, a 'mixed magnetic state' comes into existence when the weakly interacting finite spin clusters freeze (the freezing process in not cooperative in the sense that not all of the clusters freeze at the same temperature; freezing occurs over an extended range of temperatures [3] because of the distribution in cluster size and hence in cluster relaxation times) in random orientations and coexist with the (itinerant) FM matrix for temperatures below T RE . In the mixed state, the coercivity increases steeply [23], particularly for T < T f , as a result of the pinning of domain walls by the frozen FM clusters embedded in the FM matrix. The irreversibility of the low-field magnetization at low temperatures and the precipitous decline in M ZF C for T < T f can be satisfactorily explained by properly correcting [24] for the self-demagnetizing effects brought about by the presence of the exponentially increasing coercivity and the concomitant magnetic hardness (magnetic anisotropy energy).…”

Detailed ferromagnetic resonance study of amorphous Fe-rich alloys. I: re-entrant behaviour and low-lying magnetic excitations

“…The nature of low-lying magnetic excitations in a-Fe 90+y Zr 10−y (0 y 3) alloys has lately given rise to much controversy. While Krishnan et al [4] found that the 'infield' magnetization varies with temperature as M(H, T ) ∝ T 3/2 for T > T * (H ) in external magnetic fields up to 140 kOe for a-Fe 90 Zr 10 and that the spin-wave (SW) stiffness coefficient D increases with increasing H , attaining a maximum value of 39.1 meV Å2 , Beck and Kronmüller [5] observed that the thermal demagnetization in the temperature range 4.2 K T 0.5T C is solely due to Stoner single-particle (SP) excitations (SW excitations) for H < 2.7 kOe (H > 2.7 kOe) and D decreases from 50 to 35 meV Å2 as H is increased from 2.7 to 40 kOe. The observation based on inelastic neutron scattering (INS) experiments on a-Fe 91 Zr 9 , that no propagating features [6] were evident at any temperature below T C for the wavevector transfer range 0.05 Å−1 q 0.12 Å−1 , complicated the issue further.…”

Μελέτη Αλλαγών Φάσης Με Σκέδαση Νετρονίων Σε Μικρές Γωνίες.

“…(13.14). υαλώδεις δομές σπιν (ΥΔΣ, x=7), στις οποίες λαμβάνει χώρα μόνο μια μετάβαση από την παραμαγνητική στην υαλώδη κατάσταση σπιν σε θερμοκρασία T g [Hiroyoshi and Fukamichi 1981, Kaul 1983, Read et al 1984, Beck and Kronmueller 1985. Η θερμοκρασία T c μεταβάλλεται έντονα με τη συγκέντρωση και Για το σύστημα Fe9oZr I0 οι θερμοκρασίες μετάβασης στη σιδηρομαγνητική κατάσταση και στην κατάσταση υαλώδους δομής σπιν έχουν βρεθεί T c =210 Κ και Tf=80 Κ, αντίστοιχα [Hiroyoshi and Fukamichi 1981, 1983, Obi et al 1982, Krishman et al 1984 .…”