Experimental first order reversal curves (FORC) on Ising and

Heisenberg spin glasses

Didier Hérisson, Michael Östh and Per NordbladUppsala University

Hysteresis loops on spin glasses

(From Spin Glasses, R. Rammal and J. Souletie, notes froma course at Grenoble in 1981)

Au(Fe) – E.I. Kondorski et al. (1973)

Cu(Mn)-P. Monod et al.(1979)

What can one learn from the hysteresis behaviour using FORCs?

• The FORC distribution gives a visualisation of switching events• Comparison with ’related’ systems• Distinguishes an in-field SG phase from no in-field SG phase?

The FORC method

Roberts et al. J. Geophys. Res. 105, 28461 (2000)

Construction of the FORC distribution

2 ( , )

, r ar a

r a

M H HH H

H H

2

2

a rc

a rb

H HH

H HH

FORC distributions

C.R. Pike et al. Geophys. J. Int. 145, 721 (2001)

b) Weakly interactingnanoparticlesc) Floppy disc.d) nanoparticles

Monte Carlo 2d-EASG

H. G. Katzgraber et al. Phys. Rev. Lett. 85, 257202 (2002)

3D FORC distribution plot from MC-simulations of a 2d Ising EASG

H.G. Katzgraber et al.

ZFC-FC-TRM

FMTO Ag(Mn)

H=0.1 Oe

Hysteresis of Ag(Mn) and Fe0.5Mn0.5TiO3

FORC FMTOM (arb.units.)

FORC distribution FMTO

FORCs Ag(Mn)

FORC distribution Ag(Mn)

3D FORC Ag(Mn)

Comparison

Ag(Mn) FMTO

Conclusions

Remarkably different hysteresis behaviour for Ising (strongly anisotropic) and Heisenberg spin glasses.The FORCs of FMTO shows similarities with weakly interacting nanoparticle systems with wide distributions of particle sizes.The Ag(Mn) system yields unique FORC distributions with a very sharp structure at a rather weak negative bias field and low coercivity……Supportive of other experimental indications suggesting in-field SG transitions in weakly anisotropic systems?

FeAgW – mechanically alloyed

FeAgW - FORC

c.f. FMTOFeAgW