Events in Physics
CMP seminar - Zsolt Gercsi, Imperial College
Location: PS0.17a
The magnetocaloric effect (MCE) is the change of temperature of a material in a changing magnetic field, and was first observed in iron by Warburg. It has until now been exploited in paramagnetic salts as a means of cooling below the temperature of liquid Helium. However, the high global warming potential of conventional HFC refrigerants and the large fraction of energy used for cooling are concerns that currently fuel interest in such "magnetic cooling" as a high-efficiency solid-state method of refrigeration close to room temperature.
Many of these candidate materials are Mn-containing orthorhombic
(Pnma,62) structures such as MnAs, MnFe(As,P) or CoMnSi with complex non-collinear magnetic nature. We have recently shown that in CoMnSi [1], there is a large and opposing change in the two shortest Mn-Mn distances, of around 2% with the increase of temperature. This change brings about an Invar-like effect in sample volume in zero magnetic field and it also couples strongly to the suppression of helimagnetism in finite magnetic fields and brings about a tricritical point, with enhanced magnetocaloric and magnetostrictive effect .
These new experimental findings shed light on the criticality of the closest Mn-Mn separations in these MnP-type orthorhombic structures.
Therefore, we investigated the structural conditions for metamagnetism in MnP and related materials using Density Functional Theory. We found that a particular Mn-Mn separation plays the dominant role in determining the change from antiferromagnetic to ferromagnetic order in such systems and an excellent correlation between our calculations and structural and magnetic data from the literature was established [2].
Based on our calculations it should be possible to find new Mn-containing alloys that possess field-induced metamagnetism and associated magnetocaloric effects.
[1] Giant magneto-elastic coupling in a metallic helical metamagnet A. Barcza, Z. Gercsi, K.S. Knight, K.G. Sandeman submitted to PRL
http://xxx.soton.ac.uk/abs/1003.1206
[2] Structurally driven metamagnetism in MnP and related Pnma compounds Z. Gercsi, K.G. Sandeman accepted in PRB
http://arxiv.org/abs/1003.5193
Many of these candidate materials are Mn-containing orthorhombic
(Pnma,62) structures such as MnAs, MnFe(As,P) or CoMnSi with complex non-collinear magnetic nature. We have recently shown that in CoMnSi [1], there is a large and opposing change in the two shortest Mn-Mn distances, of around 2% with the increase of temperature. This change brings about an Invar-like effect in sample volume in zero magnetic field and it also couples strongly to the suppression of helimagnetism in finite magnetic fields and brings about a tricritical point, with enhanced magnetocaloric and magnetostrictive effect .
These new experimental findings shed light on the criticality of the closest Mn-Mn separations in these MnP-type orthorhombic structures.
Therefore, we investigated the structural conditions for metamagnetism in MnP and related materials using Density Functional Theory. We found that a particular Mn-Mn separation plays the dominant role in determining the change from antiferromagnetic to ferromagnetic order in such systems and an excellent correlation between our calculations and structural and magnetic data from the literature was established [2].
Based on our calculations it should be possible to find new Mn-containing alloys that possess field-induced metamagnetism and associated magnetocaloric effects.
[1] Giant magneto-elastic coupling in a metallic helical metamagnet A. Barcza, Z. Gercsi, K.S. Knight, K.G. Sandeman submitted to PRL
http://xxx.soton.ac.uk/abs/1003.1206
[2] Structurally driven metamagnetism in MnP and related Pnma compounds Z. Gercsi, K.G. Sandeman accepted in PRB
http://arxiv.org/abs/1003.5193