Surface‐Confined Molecular Coolers for Cryogenics

Abstract

An excellent molecule-based cryogenic magnetic refrigerant, gadolinium acetate tetrahydrate, is here used to decorate selected portions of silicon substrate. By quantitative magnetic force microscopy for a variable applied magnetic field near liquid-helium temperature, the molecules are demonstrated to hold their magnetic properties intact, and therefore their cooling functionality, after their deposition. These results represent a step forward towards the realization of a molecule-based micro-refrigerating device at very low temperatures.

Rotating Magnetocaloric Effect in an Anisotropic Molecular Dimer

“…[2] In contrast to this trend, we here present the first study on the rotating anisotropic MCE for amolecular compound, namely dysprosium acetate tetrahydrate,[ {Dy(OAc) 3 Figure 2a) [11,12] -its Gd 3+ analog (2)w as already shown to be an excellent and versatile magnetic refrigerant. [13,14] The crystal-field anisotropy in the Dy 3+ ion, the ground state of which is 6 H 15/2 (4f 9 , J = 15/2, S = 5/2, L = 5, g J = 4/3), plays the crucial part in determining the magnetic properties. [15] Our measurements show that, for instance,s tarting from the normal boiling temperature of 4 He (4.2 K) and in astatic field of 5T ,single-crystal samples of 1 cool down to 2K,following as ingle 908 8-rotation that changes the orientation of B from being perpendicular to the crystallographic bc plane to parallel to the c axis.S imilar temperature gradients are routinely attained by pumping liquid helium.…”

Molecule-Based Magnetic Coolers: Measurement, Design and Application

“…One can easily understand that the stray-field flux lines gradually change their direction, till reaching the inversion, on approaching the border of the drop. Accordingly, the magnetic interaction between tip and sample changes from attractive to repulsive depending on the orientation of these flux lines, therefore shifting the resonance from lower (darker) to higher (brighter) frequencies, Importantly, a quantitative analysis of the magnetic contrast reveals that the (T, H)-dependence of the ∆f measurements can be directly associated to the magnetization of bulk {Gd 2 }, enabling us to conclude that the asdeposited molecules hold intact their magnetic characteristics and, consequently, the cooling functionality as well [28]. Transferring a known, excellent cryogenic magnetocaloric material, such as the {Gd 2 } molecular nanomagnet, from bulk crystal to a silicon substrate without deterioration of its properties paves the way towards the realization of a molecule-based microrefrigerating device for very low temperatures.…”

“…From the very recent literature [28], we report the first study by magnetic force microscopy (MFM) of molecular coolers deposited on a Si substrate, as an intermediate step towards the interfacing of these molecules with a future Si-based thermal sensor designed to function as a microrefrigerator. This work specifically refers to the {Gd 2 } molecular nanomagnet ( Fig.…”

“…[28], consisting of a MFM tip positioned at a constant height ≈ 150 nm from the Si substrate and a {Gd 2 } droplet, whose height is ≈ 10 nm, while the lengths of the two oval axes are ≈ 1.7 µm and ≈ 1.4 µm, respectively. The it is here directly proportional to the stray field generated by the drop [28]. Each MFM image is accompanied by the corresponding profile along a line bisecting the droplet.…”

Theoretical design of molecular nanomagnets for magnetic refrigeration

“…22 In addition, the possibility of grafting MNMs to surfaces opens the perspective of building micron-and submicron-sized cooling devices for those instruments where local refrigeration down to very-low temperatures is needed. [23][24][25] The temperature range where MNMs display a large MCE is below T ' 10 K. This feature makes them appealing for low-temperature cryogenic applications. In fact, they have been suggested as an alternative to the expensive 3 He-4 He dilution refrigerators, thus covering a temperature range below that achieved with liquid Helium cryostats (i.e., T < 4:2 K or T < 2 K).…”