Influence of strain and polycrystalline ordering on magnetic properties of high moment rare earth metals and alloys

Abstract

Despite being the most suitable candidates for solenoid pole pieces in state-of-the-art superconductorbased electromagnets, the intrinsic magnetic properties of heavy rare earth metals and their alloys have gained comparatively little attention. With the potential of integration in micro-and nanoscale devices, thin films of Gd, Dy, Tb, DyGd and DyTb were plasma-sputtered and investigated for their in-plane magnetic properties, with an emphasis on magnetisation vs. temperature profiles. Based on crystal structure analysis of the polycrystalline rare earth films, which consist of a low magnetic moment FCC layer at the seed interface topped with a higher moment HCP layer, an experimental protocol is introduced which allows the direct magnetic analysis of the individual layers. In line with the general trend of heavy lanthanides, the saturation magnetisation was found to drop with increasing unit cell size. In-situ annealed rare earth films exceeded the saturation magnetisation of a high-moment Fe 65 Co 35 reference film in the cryogenic temperature regime, proving their potential for pole piece applications; however as-deposited rare earth films were found completely unsuitable. In agreement with theoretical predictions, sufficiently strained crystal phases of Tb and Dy did not exhibit an incommensurate magnetic order, unlike their single-crystal counterparts which have a helical phase. DyGd and DyTb alloys followed the trends of the elemental rare earth metals in terms of crystal structure and magnetic properties. Inter-rare-earth alloys hence present a desirable blend of saturation magnetisation and operating temperature.

Controlled nanocrystallinity in Gd nanobowls leads to magnetization of 226 emu/g

“…al. 25 , who studied hcp phase formation in thin films, found up to 2% hcp phase content and identified lattice size distortion and strain as being modulated by the deposition conditions. according to Bertelli et.…”

“…There have been several reports 1,25 of Gd thin films preferring to nucleate at a seed boundary in a paramagnetic fcc phase. Since the substrate (curved surface of amorphous silica here) affects the growth, other choices of geometries and materials such as Mn, Pd, Cr or W would be expected to lead to different magnetic properties.…”

“…Since the substrate (curved surface of amorphous silica here) affects the growth, other choices of geometries and materials such as Mn, Pd, Cr or W would be expected to lead to different magnetic properties. 28 The polycrystalline nature 23 of the samples, randomly grain formations, 10,11,18,23,25 crystal defects 11 and stress 18,25,29 likely act as barriers to achieving high magnetism by distorting the magnetization uniformity.…”

Ferromagnetism in DyRh and DyRhX (X = Fe, Ni, Co, Gd) thin films

“…Sample preparation and magnetometry were done in the manner described previously [17]. Following our practice for polycrystalline Dy films [19], the terminology "maximum magnetization" or "high-field (spontaneous) magnetization" The relative uncertainty of the magnetization values is approximately ΔM/M = 6% (discussion in [27]). The uncertainty of the temperatures is dictated by the according step size of the scan.…”

Hydrogen Absorption in Gd Thin Films

“…Gadolinium is a nearly ideal soft-magnetic material due to the small magnetic anisotropy [1,2]. However, one cannot take advantage of its properties because at room temperature (RT) Gd loses the ferromagnetic ordering.…”