The critical temperature of thin Fe layers on Ir(100) is measured through Mößbauer spectroscopy as a function of the layer thickness. From a phenomenological finite-size scaling analysis, we find an effective shift exponent λ = 3.15 ± 0.15, which is twice as large as the value expected from the conventional finite-size scaling prediction λ = 1/ν, where ν is the correlation length critical exponent. Taking corrections to finite-size scaling into account, we derive the effective shift exponent λ = (1 + 2∆1)/ν, where ∆1 describes the leading corrections to scaling. For the 3D Heisenberg universality class, this leads to λ = 3.0 ± 0.1, in agreement with the experimental data. Earlier data by Ambrose and Chien on the effective shift exponent in CoO films are also explained.
Due to size effecf the decrease of the Curie temperature of a ferromagnetic film with its thickness is now well established on both experimental and theoretical points of view [I]. However, the Curie temperature variation with the thickness was always considered as continuous when the thickness was varied from n lo n+l atomic planes. In other words, the Curie temperature was assumed to only depend on the quantity of deposited material. We have shown that in the particular case of thin Fe films grown on Ir(100) by MBE, two magnetic transitions are observed in a thin Fe film with a fractional number of deposited monolayers (ml) [I]. The Curie temperahlres (Tc) were determined by both Mossbauer spectroscopy and ac susceptometry. For an integer number of Fe atomic planes, we observed only one peak in the susceptibility measurement, corresponding to Tc=60K for 4 ml and Tc=14OK for 5 ml, as shown in fig. la.However, for a series of sample with a Fe thickness varying from 4 to 5 ml, we did not observe a unique peak located between 60 and 140K as usually observed, but two peaks, one located near 60K and the other near 140K. as shown in fig. Ib. ,. I.'-'--1 _ _~ . ., ... InIan8 Solans 6 rlans : susceptibility measuremen@ showing the Fimre Ib : same measurements variation of the Curie temperature for an integer with varying the Fe thickness number of Fe planes. between 4 and Splanes.In fact, as the Fe growth on Ir(lO0) is layer by layer, the morphology of a 4 t x ml (O
In this paper, the interrelation between structural and magnetic properties of ultra-thin Mn films epitaxially grown on (001) bcc Fe is studied. The Mn growth and in-plane structure were controlled by electron diffraction (RHEED). The structures of the Mn films were determined by using X-Ray absorption spectroscopy (SEXAFS). Finally, the magnetic properties were studied by using X-Ray magnetic circular dichroïsm (XMCD). All the experiments were performed under ultra-high vacuum. As shown by XMCD experiments, a magnetic transition is observed at 2 Mn monolayers. The analysis of RHEED and SEXAFS experimental results clearly demonstrates that a structural transition comes with this magnetic transition.
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