Polarized Positron Annihilation in Ferromagnets

Berko, S.; Zuckerman, Joel L.

doi:10.1103/physrevlett.13.339

Cited by 40 publications

(12 citation statements)

References 8 publications

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“…An experiment was performed on the perovskite crystal in which angular correlation curves were run with the magnetization vector first in the direction of the positron beam entering the sample and then opposite t o the direction. Similar experiments [7,8] on Fe and Ni showed a considerable polarization effect, while for the perovskite crystal considered here the angular distribution were independent of the orientation of the crystal in the magnetic field. This leads us to conclude that there are virtually no positions annihilating with the magnetic 3d-electrons in (LaO.7PbO.S)MnO,* …”

Section: S Y Chuang and B G Hwgsupporting

confidence: 80%

Positron Annihilation in Alnico and (La_0.7Pb_0.3)MnO₃

Chuang

Hogg

1967

Physica Status Solidi (b)

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A study of the angular correlation of annihilation photons from positrons annihilating in alnico and single crystals of the perovskite (La0.7Pb0.3)MnO, has been made. It is possible to account for the observed angular distributions by a simple-minded consideration of the physical properties of the two materials.Eine Unterauchung der Winkelkorrelation der Positron-Vernichtungsstrahlung in Alnico und (Lao,7Pbo.3)Mn03 wird beschrieben. Die beobachtete Winkelverteilung kann durch eine einfache Betrachtung der physikalischen Eigenschaften der beiden Stoffe erkliirt werden.

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Section: S Y Chuang and B G Hwgsupporting

confidence: 80%

Positron Annihilation in Alnico and (La_0.7Pb_0.3)MnO₃

Chuang

Hogg

1967

Physica Status Solidi (b)

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“…Spin-polarized positron sources and beams have been used for 50 yr to measure electron spin momentum distributions in ferromagnets [6], observe surface magnetism [7], search for the origin of optical activity in biological molecules [8], and study fundamental interactions [9,10]. With the advent of high density positron pulse techniques, the possibility of producing a Bose-Einstein condensate (BEC) of spin-polarized Ps atoms [11] has made it imperative to demonstrate some means of forming a fully spinpolarized collection of Ps.…”

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confidence: 99%

Production of a Fully Spin-Polarized Ensemble of Positronium Atoms

2010

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Long-lived |m|=1 positronium (Ps) atoms are produced in vacuum when high density bursts of positrons with net polarization p{0} are implanted into a porous silica film in a 2.3 T magnetic field. We observe a decrease in the |m|=1 population as the density of the incident positron beam is increased due to quenching interactions between oppositely polarized Ps atoms within the target. Saturation of this density dependent quenching indicates that the initial positron spin polarization p{0}=28+/-1%, and demonstrates the long term (10{2} s) survival of positron polarization in a Surko-type buffer gas trap. We conclude that, at high Ps densities, the minority spin component is essentially eliminated and the remaining Ps is almost entirely (approximately 96%) polarized, as required for the formation of a Ps Bose-Einstein condensate.

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“…By observing the effect of the reversal of the applied field on the annihilation irradiation from magnetized iron Hanna and Preston [15] found that the e+ emitted from a 64Cu source were partially polarized parallel to their direction of motion, that they had retained a substant,ial part of their polarization a t the time of their annihilation in the sample, and that change of the two-quantum annihilation characteristics in the high-momenturn region could be ascribed t o e+ annihilation with spin-polarized d-electrons. This work was extended and improved by Hanna and Preston 1161, Berko and Zuckerman [17], and Mijnarends and Hambro [lS]. The last-mentioned authors concluded that the spin polarization of the conduction electrons annihilating with polarized e' in a-iron is opposite to that of the d-electrons.…”

Section: General Discussion and Theoretical Backgroundmentioning

confidence: 86%

The Study of Positron Diffusion in Solids by Positron Spin Relaxation (e+SR) Experiments

Seegee

Major

Banhart

1987

Phys. Stat. Sol. (a)

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A method is given for investigating the temperature dependence of the positron (e+) diffusivity that is analogous to the study of the diffusion of positive muons in solids through the longitudinal relaxation of the muon spin polarization. It makes use of the facts that e+ emitted from radioactive sources with velocity v are longitudinally polarized with helicity v/c and that the e+ spin polarization is essentially preserved during the implantation and slowing-down process. The residual polarization of the annihilating e+ is determined by their "magnetic history", i.e., by the magnetic fields "seen" by the e+ magnetic moments during their movement through the solid. Information on the residual polarization may be obtained by measuring the annihilation characteristics (in the present set-up the Doppler broadening of the 2y annihilation line) in magnetically saturated ferromagnetic substances. I n this case the "polarimeter" serves also as the sample in which the e+ diffusivity is studied. The theory relating the polarization t o the e+ diffusivity is developed for the specific case of a-iron. Experiments on a-iron single crystals between 77 and 770 K indicate that the mechanism of e+ diffusion is rather complicated and cannot be adequately described by propagation in band states or hopping alone. Eine Methode zur Bestimmung der Temperaturabhangigkeit des Positronendiffusionskoeffizienten wird vorgestellt, die darauf beruht, daD von einer radioaktiven Quelle mit der Geschwindigkeit v emittierte Positronen mit der Helizitit v/c longitudinal polarisiert sind, und die enge Analogien zur Untersuchung der Diffusion positiver Myonen mit Hilfe der Myonspinrelaxation aufweist. Die Spinpolarisation der Positronen bleibt beim Eindringen in die Probe und beim Abbremsvorgang weitgehend erhalten. Die bei der Zerstrahlung noch vorhandene Restpolarisation wird durch die ,,magnetische Vorgeschichte" der Positronen bestimmt, d. h. durch die Magnetfelder, rnit denen ihre magnetischen Momente wahrend der Diffusion durch die Probe wechselwirken. Information uber die Restpolarisation kann durch Messen der Zerstrahlungscharakteristik (im vorliegenden Experiment der Dopplerverbreiterung) in magnetisch gesattigten ferromagnetischen Substanzen gewonnen werden. Hierbei dient die Probe, in der die Positronendiffusion untersucht wird, auch als Polarimeter. Die zur Verknupfung der Depolarisierung mit dem Diffusionskoeffizienten der Positronen benotigte Theorie wird fur den speziellen Fall von a-Eisen entwickelt. Ihre Anwendung auf experimentelle Ergebnisse an a-Eiseneinkristallen zwischen 77 und 770 K zeigt, da13 der Diffusionsmechanismus der Positronen recht kompliziert ist und nicht ausschlieBlich mit der Positronenausbreitung in Bandzustlnden oder rnit Hupfprozessen zutreffend beschrieben werden kann.

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Polarized Positron Annihilation in Ferromagnets

Cited by 40 publications

References 8 publications

Positron Annihilation in Alnico and (La_0.7Pb_0.3)MnO₃

Positron Annihilation in Alnico and (La_0.7Pb_0.3)MnO₃

Production of a Fully Spin-Polarized Ensemble of Positronium Atoms

The Study of Positron Diffusion in Solids by Positron Spin Relaxation (e+SR) Experiments

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Polarized Positron Annihilation in Ferromagnets

Cited by 40 publications

References 8 publications

Positron Annihilation in Alnico and (La0.7Pb0.3)MnO3

Positron Annihilation in Alnico and (La0.7Pb0.3)MnO3

Production of a Fully Spin-Polarized Ensemble of Positronium Atoms

The Study of Positron Diffusion in Solids by Positron Spin Relaxation (e+SR) Experiments

Contact Info

Product

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Positron Annihilation in Alnico and (La_0.7Pb_0.3)MnO₃

Positron Annihilation in Alnico and (La_0.7Pb_0.3)MnO₃