Abstract
Random field induced spontaneous excess moments appear in field cooled single crystals of diluted Ising antiferromagnets. Here we report results from low temperature measurements of field cooled (including zero field) magnetic hysteresis loops parallel and perpendicular to the c-axis of a single crystal of composition Fe0.6Zn0.4F2. We find that weak static ferromagnetic excess moments attained on field cooling give rise to an apparent exchange bias of the magnetic hysteresis loops, whose magnitude is controlled by temperature and the strength and direction of the cooling field. Random field induced temporal excess moments only become observable in cooling fields larger than 1 T applied along the c-axis direction of the Fe0.6Zn0.4F2 single crystal.
Highlights
Random field induced spontaneous excess moments appear in field cooled single crystals of diluted Ising antiferromagnets
A dilute Ising antiferromagnet in a homogeneous magnetic field (DAFF)[10,11,12] is a replica of the random field Ising model (RFIM)13. FeF2 diluted by diamagnetic dopant Zn ( Fe1-xZnxF2 (FZF)) has been extensively used as experimental model systems of a random exchange Ising model (REIM) system in zero applied field and RFIM system in an applied field[14,15,16,17,18]
The field and temperature dependence of the magnetization measured parallel and perpendicular to the c-axis of the dilute Ising antiferromagnet F e0.6Zn0.4F2 reveal apparent exchange bias effects governed by static excess moments, which at higher fields in the case of H||c-axis are enhanced by random field induced temporal excess moments. HEB amounts to ~ 5kOe at 2 K ( HFC = 5 T)
Summary
Random field induced spontaneous excess moments appear in field cooled single crystals of diluted Ising antiferromagnets. At temperatures below the Néel temperature, TN = 78.4 K, of FeF2 an excess magnetic moment develops, that near T N decays with a critical exponent characteristic of 3d Ising s ystems[5] This excess moment gives rise to an apparent exchange bias associated with the vertical shift of the hysteresis loops occurring when cooling the sample through TN in a finite magnetic field[6]. The excess moment is rigidly locked to the cooling field direction and is virtually unaffected by any magnetic field changes in the antiferromagnetic state This is reflected in a field dependent rapidly saturating thermo-remnant magnetization (TRM) and zero isothermal remnant magnetization (IRM) at all accessible fields and temperatures below TN6. We examine the temperature and field dependence of the parallel and perpendicular magnetization of a Fe0.6Zn0.4F2 single crystal with special emphasis on apparent exchange bias and the effects of random fields by comparing the parallel and the perpendicular magnetization behaviors
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