Role of disorder when upscaling magnetocaloric Ni-Co-Mn-Al Heusler alloys from thin films to ribbons

Abstract

Research in functional magnetic materials often employs thin films as model systems for finding new chemical compositions with promising properties. However, the scale-up of thin films towards bulk-like structures is challenging, since the material synthesis conditions are entirely different for thin films and e.g. rapid quenching methods. As one of the consequences, the type and degree of order in thin films and melt-spun ribbons are usually different, leading to different magnetic properties. In this work, using the example of magnetocaloric Ni-Co-Mn-Al melt-spun ribbons and thin films, we show that the excellent functional properties of the films can be reproduced also in ribbons, if an appropriate heat treatment is applied, that installs the right degree of order in the ribbons. We show that some chemical disorder is needed to get a pronounced and sharp martensitic transition. Increasing the order with annealing improves the magnetic properties only up to a point where selected types of disorder survive, which in turn compromise the magnetic properties. These findings allow us to understand the impact of the type and degree of disorder on the functional properties, paving the way for a faster transfer of combinatorial thin film research towards bulk-like materials for magnetic Heusler alloys.

The Effect of Different Atomic Substitution at Mn Site on Magnetocaloric Effect in Ni50Mn35Co2Sn13 Alloy

“…The as-cast samples were wrapped by tantalum foil and annealed in a high-vacuum quartz tube at 1173 K for 96 h, followed by quenching in ice water. It is noted that the effect of different heat treatments on the magnetic and magnetocaloric properties has been studied intensively in NiMn-based Heusler alloys [22][23][24][25]. It is revealed that the MCE can be largely improved by optimizing the heat treatment, e.g., an optimized annealing method can reproduce the excellent functional properties of Ni-Co-Mn-Al films in ribbons [25].…”

“…It is noted that the effect of different heat treatments on the magnetic and magnetocaloric properties has been studied intensively in NiMn-based Heusler alloys [22][23][24][25]. It is revealed that the MCE can be largely improved by optimizing the heat treatment, e.g., an optimized annealing method can reproduce the excellent functional properties of Ni-Co-Mn-Al films in ribbons [25]. Here, we chose the same heat treatment from Reference [17], which also studied Ni 50 Mn 34 Co 2 Sn 14 and presented giant MCE in this alloy.…”

Effect of substitutional doping and disorder on the phase stability, magnetism, and half-metallicity of Heusler alloys

“…We also mix Mn with Fe in Co 2 (Mn 1−x Fe x )A, where A is Sn or Sb, and 0 ≤ x ≤ 1. We show that in fH Co 2 MnX alloys, the width of the minority-spin band gap E gap decreases along the period (3)(4)(5)(6) and increases along the group (13-16) of X.…”

“…Heusler alloys [1] are a large class of naturally occurring [2] and manufactured [3] ternary intermetallic compounds with L2 1 full Heusler (fH) or C1 b half-Heusler (hH) structure (sometimes called semi-Heusler), which can be partially disordered [4][5][6][7][8][9][10]. Many Heuslers are ferromagnetic (FM), with Curie temperatures T c between 200 and 1100 K [11][12][13].…”

Nano Scaled Checkerboards: A Long Range Ordering in NiCoMnAl Magnetic Shape Memory Alloy Thin Films with Martensitic Intercalations

“…A special class of magnetic shape memory alloys are Heusler compounds such as NiMnX (X = Al, Ga, Sn, In), which are considered as promising materials for magnetocaloric cooling applications due to their magnetoelastic coupling near room temperature [10][11][12]. However, most of the compounds show a large thermal hysteresis, which limits their potential in future applications [13][14][15]. Therefore, efficient mechanisms to change the martensitic transformation behavior have to be identified.…”