Temperature modulation studies of the magnetic susceptibility of polycrystalline dysprosium are compared with measurements of minor loop temperature hysteresis of susceptibility in both the ferromagnetic and the spiral spin antiferromagnetic regions. The effects of temperature hysteresis upon susceptibility in the ferromagnetic and antiferromagnetic regions, and the intermediate region which links them, are examined.Temperaturmodulationsuntersuchungen der magnetischen Suszeptibilitlit von polykristallinem Dysprosium werden mit Messungen der kleineren Temperatur-Hystereseschleifen der Suszeptibilitat sowohl in ferromagnetischen als auch im antiferromagnetischen Spiral-Spin-Bereich verglichen. Die Einfliisse der Temperaturhysterese auf die Suszeptibilitiit im ferromagnetischen und antiferroma.gnetischen Bereich und dem Zwischenbereich, der beide verbindet, werden untersucht.Recently we reported ac susceptibility and transient enhancement (TE) studies of polycrystalline gadolinium [4, 51, dysprosium [6] and of a terbium single crystal [7]. T E measurements, wherein a second ac (or pulsed dc) field is applied a t afrequency differing from the primary, was shown to be a sensitive indicator of the presence of domain wall pinning with the enhanced susceptibility being caused by the freeing of the walls by the second field [5]. For gadolinium, T E studies indicate the nucleation of the ferromagnetic walls a t the Curie temperature, T,, and their presence a t lower t,emperatures. For terbium and dysprosiuni the TE studies indicate not only the presence of ferromagnetic domain walls below T, but also the formation, via an interl) Duntroon, ACT 2600 New South Wales, Australia. z, P. 0. Box 4, Canberra, ACT 2600, Australia.

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A low-temperature spin-polarized scanning tunneling microscope operating in a fully rotatable magnetic field Rev. Sci. Instrum. 80, 023708 (2009); 10.1063/1.3086428 Field controlled magnetic thermal hysteresis in Co ∕ Tb multilayersThe Fourier components of the ferromagnetic hysteresis of polycrystalline gadolinium and terbium have been measured in low ac magnetic fields (0.1-15 A m-I ) using synchronous detection. The field dependences and magnitudes of the various harmonics cannot be described by the Rayleigh hysteresis law. It is shown that the dominant term in the absorptive component of the first harmonic is associated with a magnetic aftereffect. At the lowest fields (H S 1 A m -I) there are indications that magnetic hysteresis vanishes.

Detailed measurements of the AC magnetic susceptibility ~' ( 7) and its response S ( T ) = A,y'(T)/ATto a thermal modulation wave have been carried out around the narrow helical antiferromagnetic (AF) region (about 221-27.9 K) of a high-purity single crystal of terbium. along its magnetically easy b axis. We have extended existing theories of AF susceptibilityolspiralspinstructurestodemonstratethdt the number ofspinsin theintervening domain wall should decrease with increasing temperature. The ~' ( 7 ) and S(T) results obtained on cooling into, and warming from, the AF region, without crossing T,, are consistent with this theory. SignificantlyenhancedAFsusceptibilityandcorrespondingeff~ts in S( 7) are observed on warming from the ferromagnetic region into the AF region. This behaviour can be accounted for by a spatial alignment of ferromagnetic islands centred on magnetic inclusions and/or thicker aligned domain walls of ferromagnetic character that separate AF domains of opposite chirality.

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