Effect of Non-stoichiometric Vanadium Addition on the Magnetocaloric Properties of Fe2P-type Alloys

Concepts de base

Non-stoichiometric addition of vanadium in Fe2P-type (FeMnP0.5Si0.5)1-x(FeV)x alloys can tune the magnetic ordering temperature, thermal hysteresis, and magnetocaloric effect by modifying the Fe-moment localization and magnetoelastic coupling.

Résumé

The study investigates the effect of non-stoichiometric vanadium (V) addition on the magnetocaloric properties of Fe2P-type (FeMnP0.5Si0.5)1-x(FeV)x alloys (x = 0, 0.01, 0.02, 0.03).
Key highlights:

Density functional theory calculations confirm the preferred 3g-site occupancy of V in the hexagonal Fe2P structure.
The magnetic ordering temperature decreases with increasing V content due to reduced ferromagnetic coupling between the magnetic atoms.
The isothermal entropy change (ΔSM) and adiabatic temperature change (ΔTad) decrease with increasing V, which is attributed to the reduced Fe-moment localization in the paramagnetic state.
The thermal hysteresis (ΔThyst) of the magnetoelastic phase transition decreases with V addition, improving the mechanical stability of the alloys.
The ΔTad of 1.7 K at 1.9 T is observed for the x = 0.02 alloy, with the irreversibility of ΔTad related to the latent heat of the magnetoelastic transition.
The non-stoichiometry in the non-metallic site influences the formation of the secondary (Fe,Mn)3Si phase, which cannot be directly correlated to the magnetoelastic coupling strength.

Stats

The saturation magnetization (MS) decreases from 154 Am2/kg for x = 0 to 134 Am2/kg for x = 0.03.
The isothermal entropy change (ΔSM) decreases from 16.5 J/kg·K for x = 0 to 7.7 J/kg·K for x = 0.03 at a 2 T magnetic field.
The adiabatic temperature change (ΔTad) is 1.7 K at 1.9 T for the x = 0.02 alloy.

Citations

"The non-stoichiometric addition in the P/Si-site may also influence the MC effect by changing the metal to non-metal ratio in the alloy."
"The value of ΔThyst decreases as expected with increasing V addition in the metal site of the alloy."
"The observed values of ΔTad for the x = 0.02 alloy, measured following continuous cooling and discontinuous cooling protocols, are due to the thermal hysteresis ΔThyst of the alloy."

Idées clés tirées de

Hysteresis design of non-stoichiometric Fe2P-type alloys with giant magnetocaloric Effect

by Saga... à arxiv.org 10-03-2024

https://arxiv.org/pdf/2410.01747.pdf

Questions plus approfondies

How does the formation of the secondary (Fe,Mn)3Si phase impact the overall magnetocaloric performance of the non-stoichiometric Fe2P-type alloys?

The formation of the secondary (Fe,Mn)3Si phase in non-stoichiometric Fe2P-type alloys significantly influences their magnetocaloric performance. This secondary phase contributes to the overall magnetic properties and can alter the effective magnetic interactions within the alloy. As the concentration of the secondary phase increases with the addition of vanadium (V), it leads to a more complex magnetic landscape, which can affect the magnetic ordering temperature (Tt) and the isothermal entropy change (∆SM).
The presence of the (Fe,Mn)3Si phase introduces additional magnetic interactions that can compete with the primary ferromagnetic interactions in the Fe2P-type structure. This competition can result in a decrease in the saturation magnetization (MS) and a reduction in the overall magnetocaloric effect, as observed in the study where ∆SM decreased with increasing x. Furthermore, the secondary phase can contribute to thermal hysteresis (∆Thyst), which is detrimental to the efficiency of magnetocaloric materials. The thermal hysteresis arises from the latent heat associated with the first-order magnetic phase transitions, and the presence of a secondary phase can exacerbate this effect, leading to a less efficient magnetocaloric response.

What are the potential strategies to further reduce the thermal hysteresis in these alloys while maintaining a large magnetocaloric effect?

To further reduce the thermal hysteresis (∆Thyst) in non-stoichiometric Fe2P-type alloys while maintaining a large magnetocaloric effect, several strategies can be considered:

Optimizing Composition: Fine-tuning the composition of the alloys by adjusting the ratios of Fe, Mn, and V can help minimize the formation of secondary phases that contribute to thermal hysteresis. A careful balance between the metallic and non-metallic components can enhance the stability of the primary phase and reduce the volume change associated with the phase transition.

Controlling Microstructure: Employing advanced processing techniques such as rapid solidification or controlled annealing can lead to a more homogeneous microstructure. This can help in reducing the size and distribution of secondary phases, thereby minimizing their impact on thermal hysteresis.

Introducing Alloying Elements: The addition of other alloying elements that do not significantly alter the magnetic properties but can stabilize the primary phase may help in reducing ∆Thyst. Elements that promote a more continuous phase transition or that can modify the magnetoelastic coupling without introducing significant lattice strain could be beneficial.

Utilizing Composite Structures: Developing composite materials that combine the desirable properties of different magnetocaloric materials can also be a viable approach. By layering or mixing materials with complementary properties, it may be possible to achieve a more favorable thermal hysteresis profile while retaining a strong magnetocaloric effect.

Enhancing Magnetoelastic Coupling: Investigating the effects of non-stoichiometry on the magnetoelastic coupling strength can provide insights into how to optimize the lattice parameters for a more efficient phase transition. This could involve computational modeling to predict the effects of various compositions on the magnetoelastic properties.

How can the insights from this study on Fe-moment localization be leveraged to design new rare-earth-free magnetocaloric materials with enhanced performance?

The insights gained from the study on Fe-moment localization in non-stoichiometric Fe2P-type alloys can be instrumental in designing new rare-earth-free magnetocaloric materials with enhanced performance. Here are several ways these insights can be applied:

Targeting Fe-Moment Localization: Understanding how the localization of Fe-moments affects the magnetocaloric effect allows researchers to design materials that optimize this localization. By controlling the electronic environment around Fe atoms through careful alloying and site occupancy, it may be possible to enhance the change in Fe-moment at the magnetic phase transition, thereby increasing the isothermal entropy change (∆SM).

Exploring Non-Stoichiometric Compositions: The study highlights the importance of non-stoichiometry in influencing the magnetic properties and phase transitions. Future research can focus on exploring a wider range of non-stoichiometric compositions in other magnetocaloric systems, potentially leading to the discovery of new materials with favorable magnetocaloric properties.

Designing for Mechanical Stability: The findings regarding the relationship between lattice volume change and mechanical stability can guide the design of new alloys that maintain structural integrity during phase transitions. This is crucial for practical applications where mechanical stability is essential for the longevity and reliability of magnetocaloric devices.

Utilizing Computational Methods: The computational approaches used in this study can be applied to predict the behavior of new alloy systems. By simulating the effects of different compositions and structures on Fe-moment localization and magnetocaloric performance, researchers can identify promising candidates for further experimental investigation.

Developing Hybrid Materials: Insights into the interplay between magnetic and structural properties can lead to the development of hybrid materials that combine different magnetic phases or structures. Such materials could exploit the benefits of both localized and itinerant magnetism, potentially resulting in enhanced magnetocaloric effects without the use of rare-earth elements.

By leveraging these insights, researchers can pave the way for the development of efficient, sustainable, and economically viable magnetocaloric materials suitable for a range of applications in energy-efficient refrigeration technologies.