Magnetic Properties and Magnetocaloric Effect of Pr2Co7 Compound

Magnetic Properties and Magnetocaloric Effect of Pr2Co7 Compound: Comparison

Please note this is a comparison between Version 1 by Lotfi Bessais and Version 9 by Lindsay Dong.

The Pr2Co7 compound has interesting magnetic properties, such as a high Curie temperature TC and uniaxial magnetocrystalline anisotropy. It crystallizes in a hexagonal structure (2:7 H) of the Ce2Ni7 type and is stable at relatively low temperatures (Ta ≤ 1023 K), or it has a rhombohedral structure (2:7 R) of the Gd2Co7 type and is stable at high temperatures (Ta ≥ 1223 K). Studies of the magnetocaloric properties of the nanocrystalline Pr2Co7 compound have shown the existence of a large reversible magnetic entropy change (ΔSM) with a second-order magnetic transition.

magnetic properties
magnetocaloric properties
Pr2Co7 Compound

1. Introduction

In recent years, magnetic nanomaterials based on rare-earth elements (R) and transition metals (T) have been widely investigated due to their extremely diverse potential applications in industrial fields [1,2,3,4,5,6,7,8]. These properties are often used to produce soft, hard, or semi-hard magnetic materials [9,10,11,12,13,14,15,16,17,18,19,20,21,22,23]. The origin of these exceptional magnetic properties is particularly due to the coexistence of of two complementary kinds of magnetism: the localized magnetism characteristic of rare-earth (R) electrons and the itinerant magnetism of the

3 d

electrons of transition metals (T), such as cobalt (Co) and iron (Fe) [24,25,26,27,28,29,30,31,32,33]. The R elements thus provide their strong magnetocrystalline anisotropy (H $_{a}$ ) due to the interactions between their orbital moment and the crystal field. The $3 d$ metals provide their strong magnetization and a high Curie temperature (T $_{C}$ ) due to the important exchange interactions between the $3 d$ elements [34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51]. Permanent magnets are the idea of an ever-increasing number of recent devices. Alloys and intermetallic compounds obtained by combining (R) elements with metals (T) form a crucial class of materials for which applications have been found in permanent magnets [44]. Among the intermetallic systems, the noncrystalline Pr $_{2}$ Co $_{7}$ compound is currently one of the most promising [34,52,53,54]. The interest in these systems is due to the combination of the complementary characteristics of the $3 d$ -itinerant and $4 f$ -localized magnetism of Co and Pr atoms, respectively [54,55]. In order to strengthen these interactions, it is necessary to partially substitute the Co atoms in the noncrystalline Pr $_{2}$ Co $_{7}$ compounds with an appropriate element, such as iron (Fe), or through the insertion of a light element, such as carbon (C) or hydrogen (H), which can increase interatomic distances and strengthen the magnetic moment.

3. Structural, Microstructural, and Magnetic Characterizations

The microstructural characterizations of the Pr $_{2}$ Co $_{7}$ , Pr $_{2}$ Co $_{7 - x}$ Fe $_{x}$ , Pr $_{2}$ Co $_{x}$ C $_{x}$ , and Pr $_{2}$ Co $_{x}$ H $_{x}$ samples were investigated by using X-ray diffraction (XRD; Bruker D8 Advance) with CuK $_{α}$ radiation of wavelength $λ$ = 0.154056 nm. The refinement of the patterns was done by using the FULLPROF computing code based on the Rietveld method [66,67] with the assumption of the Thompson–Cox–Hastings line profile. The goodness-of-fit indicators $χ^{2}$ and R $_{B}$

were calculated as previously described in [61]. Extended X-ray absorption fine-structure (EXAFS) measurements were performed on a 2.75 GeV SAMBA beamline, Synchrotron SOLEIL, France. EXAFS experiments were carried out at 293 K in the fluorescence mode using a 4-element Si(111) drift detector. The EXAFS spectra were extrapolated using the MAXeCherokee code [68,69], while the fitting process and comparison between theoretical and experimental EXAFS curves were carried out with the MAX-Roundmidnight package [68]. The theoretical phases and amplitudes used in the EXAFS models were determined with the FEFF8 code [70] by using the crystal structure results of the Rietveld refinements at each Fe site with the use of the MAX-CRYSTALFFREV code [68] for the Crystal Structure–EXAFS Modeling interface.

The morphology, the chemical compositions, and the images were considered using a JEOL 2010 FEG transmission electron microscope equipped with an energy-dispersive spectrometer (EDS). For the TEM measurements, specimens were thinned using a focused-ion-beam-type FEI Helios 600 Nanolab dual-beam instrument. The Curie temperature T

_{C}

was measured on a MANICS differential sample magnetometer (DSM-871 Magneto/susceptometer) in a field of 1 kOe with a sample of around 5–10 × 10 $^{- 3}$ g. T $_{C}$ was obtained from the M(T) curve by extracting the linear part of the M(T) curve and determining the temperature value of the intersection with the expanded baseline. Magnetic hysteresis M(H) loops were determined using a Physical Properties Measurement System (PPMS9) Quantum Design microscope.

4. Structural Properties

Figure 1.

Figure 2.

Figure 3.

Figure 4.

Table 5.

x	0.0	0.25	0.5	0.75	1
a (Å)	5.068(1)	5.070(3)	5.076(1)	5.079(11)	5.080(2)
c (Å)	24.456(2)	24.509(5)	25.009(3)	25.576(4)	26.981(2)
c/a	4.825	4.832	4.841	5.035	5.311
V(Å $^{3}$

)	544.02	547	555	567.4	598.9
$R_{B}$

	3.1	2.43	1.31	2.76	2.42
$χ^{2}$

3.80

3.28

3.60

3.38

3.36

Figure 5.

1. Introduction

3. Structural, Microstructural, and Magnetic Characterizations

4. Structural Properties

5. Intrinsic Magnetic Properties

6. Extrinsic Magnetic Properties