An automated technique for the measurement of the AC initial susceptibility and its disaccommodation in ferromagnetic materials

J. Phys.: Condens. Matter

1996

The ac initial susceptibility of a cobalt single crystal with [0001] orientation has been measured in the temperature range 300 to 820 K. A theoretical treatment of the susceptibility in the range 300 to 700 K has been given in terms of the contributions of domain wall displacements and magnetization vector rotations in the appropriate temperature intervals; this theoretical treatment is found to be in good agreement with the experimentally observed variation. Measurements in the range 700 to 820 K include the martensitic phase transformation at 710 K, which has a pronounced influence on the susceptibility. Magnetic relaxation measurements have also been made over the whole temperature range (300 to 820 K) and are found to be fully consistent with the interpretation of the susceptibility data. An important feature of the relaxation spectrum is a null region (584 to 710 K) which corresponds to that temperature range where contributions to the susceptibility occur due solely to magnetization rotations.

Section: Methodsmentioning

confidence: 99%

An analysis of the high-temperature initial susceptibility of single-crystal cobalt

Castro

J. Phys.: Condens. Matter

1996

“…Recently, a modernized version of this phase-locking technique has been described by Blythe [47], allowing both automated data acquisition and control of all measuring procedures using a microcomputer.…”

Section: Bridge Techniquesmentioning

confidence: 99%

A Review of the Magnetic Relaxation and Its Application to the Study of Atomic Defects in ?-Iron and Its Diluted Alloys

Kronmüller²,

Seeger³

et al. 2000

phys. stat. sol. (a)

This review presents a comprehensive survey on intensive studies performed during the last decades on point defect reactions on a-iron (a-Fe) and its diluted alloys. Our intention is to give an actual account of the knowledge accumulated on this subject, as it has been obtained predominantly by means of the magnetic after-effect (MAE) spectroscopy. After a concise introduction into the theoretical and experimental fundamentals of this technique, the main concern is focused on the presentation and detailed discussion of the MAE spectra arising ± ± after low-temperature electron (e À )-or neutron(n)-irradiation and subsequent annealing ± ± in: (i) high-purity a-Fe and a-Fe doped with (ii) substitutional solutes (like Ni, V, Al, Cu, Ti, Be, Si, Mn, . . .) or (iii) interstitial solutes (like O, H, C, N). During the course of systematic annealing treatments, these respective spectra undergo dramatic variations at specific temperatures thereby revealing in great detail the underlying intrinsic reactions of the radiation-induced defects, i.e., reorientation, migration, clustering, dissolution and finally annihilation. In alloyed Fe systems the corresponding reaction sequences are even multiplied due to additional interactions between defects and solute atoms. Most valuable information concerning formation-, dissociation-and binding enthalpies of small, mixed clusters (of the type C i V k , N i V k ; i; k ! 1) has been obtained in highpurity a-Fe base material which, after charging with C or N, had been e À -irradiated. Concerning the basic recovery mechanisms in a-Fe, two complementary results are obtained from the analysis of the various systems: (i) in high-purity and substitutionally alloyed a-Fe the recovery in Stage-III (200 K) is governed by a three-dimensionally migrating (H M I 0:56 eV) stable interstitial (dumbbell); (ii) following the formation and dissociation kinetics of small clusters (C 1 V k , N 1 V k ) in interstitially alloyed a-Fe the migration enthalpy of the monovacancy must hold the following relation H M N (0.76 eV) < H M C (0.84 eV) < H M V1 . These results are in clear agreement with the socalled two-interstitial model (2IM) in a-Fe ± a conclusion being further substantiated by a systematic comparison with the results obtained from nonrelaxational techniques, like i.e. positron annihilation (PA), which by their authors are preferentially interpreted in terms of the one-interstitial model (1IM).Die vorliegende Arbeit gibt einen umfassenden Ûberlick u È ber die wa È hrend der letzten Jahrzehnte durchgefu È hrten, eingehenden Untersuchungen der Punktfehler-Eigenschaften in a-Eisen (a-Fe) und verdu È nnten Fe-Legierungen. Demgema È û ist diese Zusammenfassung gedacht als ein dem gegenwa Èrtigen Kenntnisstand entsprechender Rechenschaftsbericht u È ber die auf diesem Gebiet, hauptsa È chlich mit Hilfe der magnetischen Nachwirkungs (MNW) ± ± Spektroskopie, gewonnenen, tiefreichenden Einsichten in diesen Problemkreis. Nach einer kurzen Einfu È hrung in die theoretischen und experimentellen Grundlagen di...

“…The present magnetic after-effect measurements were performed using a fully automated AC technique described elsewhere [9]. This method, which is based on a phasesensitive detection technique, allowed both the real and the imaginary component of the complex susceptibility, together with their time dependences, to be determined simultaneously, although here we present results for the real component only.…”

Section: Methodsmentioning

confidence: 99%

An analysis of the high-temperature magnetic after-effect in single-crystal cobalt

J. Phys. D: Appl. Phys.

Lopez-Cabido

Castro

1997

Magnetic relaxation measurements have been performed in the temperature range 300 - 820 K on a cobalt single crystal with [0001] orientation. The relaxation spectrum may be conveniently divided into three regions. Two of these, region I and region II , lie in the hexagonal phase; the third region lies in the cubic phase. In region I we have found a broad relaxation peak, whereas region II is characterized by the complete absence of any relaxation process. In the cubic phase, region III, we have observed a plateau-like magnetic relaxation process having an approximately logarithmic time dependence. An analysis of these relaxation processes is given and they are interpreted in terms of the defects present in the sample.