Magnetism and the magnetocaloric effect in PrMn 1.6 Fe 0.4 Ge 2
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Magnetism and the magnetocaloric effect in PrMn1.6 Fe0.4 Ge2 W. D. Hutchison · J. L. Wang · S. J. Campbell
Published online: 24 November 2012 © Springer Science+Business Media Dordrecht 2012
Abstract The magnetic and magnetocaloric properties of PrMn1.6 Fe0.4 Ge2 around the ferromagnetic transitions TC inter ∼ 230 K and TC Pr ∼ 30 K have been investigated by magnetisation, 57 Fe Mössbauer spectroscopy and electron paramagnetic resonance (EPR) measurements over the temperature range 5–300 K. The broad peaks in magnetic entropy around TC inter (intralayer antiferromagnetism of the Mn sublattice to canted ferromagnetism) and TC Pr (onset of ferromagnetic order of Pr sublattice in addition to ferromagnetically ordered Mn sublattice) are typical of second order transitions with maximum entropy values of -S M ∼ 2.0 J/kg K and -S M ∼ 2.2 J/kg K respectively for B = 0–6 T. The EPR signal around T = 48 K of g value g ∼ 0.8 is consistent with paramagnetic free ion Pr3+ . Below TC Pr ∼ 30 K the g value increases steadily to g ∼ 2.5 at 8 K as saturation of the Pr3+ ion is approached. The EPR measurements indicate additional effects in this system below T ∼ 20 K with the appearance of EPR signals of low g value g ∼ 0.6. Keywords Magnetisation · 57 Fe Mössbauer spectroscopy · EPR · Magnetic entropy · PrMn1.6 Fe0.4 Ge2
W. D. Hutchison · J. L. Wang · S. J. Campbell (B) School of Physical, Environmental and Mathematical Sciences, The University of New South Wales, Canberra, ACT 2600 Australia e-mail: [email protected] J. L. Wang Institute for Superconductivity and Electronic Materials, University of Wollongong, Wollongong, NSW 2522 Australia J. L. Wang Bragg Institute, Australian Nuclear Science and Technology Organisation, Menai, NSW 2234 Australia
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W.D. Hutchison, J.L. Wang
1 Introduction In addition to the continuing intrinsic interest in understanding the myriad of structural and physical properties exhibited by RMn2 X2 –based compounds (X=Si, Ge) [e.g. 1–3], such rare earth (R)-transition metal intermetallic compounds have attracted additional attention due to their magnetocaloric behaviour at selected magnetic transitions [e.g. 4–6]. For example, NdMn2 Ge0.4 Si1.6 has recently been shown to exhibit a giant magnetocaloric effect (MCE) associated with the fieldinduced first order magnetic transition (FOMT) from antiferromagnetism to ferromagnetism around TC ∼ 36 K [6]. Magnetic materials around these temperatures are relevant to cooling aspects related, for example, to magnetic refrigeration for hydrogen liquefaction [7]. The structural and magnetic behaviours of the PrMn2−x Fex Ge2 series of compounds have been investigated and the magnetic phase diagram determined [e.g. 8, 9]. Of particular interest are Mn-rich compounds around x ∼ 0.4 for which ferromagnetic transitions are obtained around TC inter ∼ 230 K and TC Pr ∼ 30 K [9]. The transition at TC inter marks the change in magnetic ordering of the Mn sublattice from in-plane intralayer antiferromagnetism (AFl) to canted ferromagnetism (Fmc) where the fe
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