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The magnetic ground state of the martensitic phase in metamagnetic shape memory alloys seems to be dependent on the analyzed system. In Ni2Mn1+xZ1−x (Z = In, Sn, and Sb) alloys, ferromagnetic and antiferromagnetic interactions coexist in the martensitic state. Different mechanisms, i.e., reentrant spin glasses, superparamagnetism, or superspin glasses have been proposed to explain the martensitic magnetic behavior. In this letter, the magnetic properties of the martensitic phase in Ni-Mn-In-Co alloys have been determined. The martensitic phase shows the presence of superparamagnetic domains inside a paramagnetic matrix. On cooling, superspin glass features occur when interacting clusters are frozen below a critical temperature.

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Precursor phenomena were investigated in a Ni-Fe-Ga alloy close to the stoichiometric Heusler composition Ni 2 FeGa. In particular, the phonon-dispersion curves, the diffuse scattering and the magnetic properties of a single crystalline Ni 51.5 Fe 21.5 Ga 27 alloy were measured as a function of temperature. The TA 2 branch along the ͓110͔ direction of the L2 1 phase shows a significant phonon softening around = 0.35 resulting in a marked dip which becomes more pronounced as the temperature decreases. Diffuse neutron-scattering measurements performed along ͓0͔ direction around Bragg reflections also reveal the presence of small satellite peaks at = 0.33 whose intensity increases on approaching the martensitic transformation temperature. Both elastic and inelastic-scattering anomalies confirm the occurrence of premartensitic phenomena in Ni-Fe-Ga alloys. The influence of an external magnetic field ͑6 T͒ on the anomalous phonon is shown to be negligible and just a small shift of the transformation temperature takes place because of the magnetic field.

The influence of defects and local stresses on the magnetic properties and martensitic transformation in Ni 50 Mn 35 Sn 15 is studied at macroscopic and atomic scale levels. We show that both the structural and magnetic properties of the alloy are very sensitive to slight microstructural distortions. Even though no atomic disorder is induced by milling, the antiphase boundaries linked to dislocations promote the antiferromagnetic coupling of Mn, resulting in a significant decrease in the saturation magnetization. On the other hand, the temperature range of the transformation is considerably affected by the mechanically induced local stresses, which in turn does not affect the equilibrium temperature between the austenitic and martensitic phases. Finally, we demonstrate that the recovery of the martensitic transformation is directly related to the intensity of the non-magnetic component revealed by 119 Sn M€ ossbauer spectroscopy. This result opens the possibility of quantifying the whole contribution of defects and the local stresses on the martensitic transformation in Ni-Mn-Sn alloys.Published by AIP Publishing. [http://dx.

Temperature dependences of the vibrational and magnetic properties of the high symmetry parent phase in three different alloys Ni 51.1 Mn 24.9 Ga 24.0 , Ni 49.7 Mn 24.1 Ga 26.2 , and Ni 49.6 Mn 21.9 Ga 28.5 are measured in the temperature range between 4.2 and 300 K. While in the first two alloys an intermediate transformation precedes the subsequent martensitic transformation ͑MT͒, the MT is not detected in the analyzed temperature range in the third one. The features of both the intermediate phase transformation and the intermediate phase in these alloys are determined. It is found that the elastic characteristics of the high symmetry phase are similar independent of the closeness of the martensitic transformation. Besides, the magnetic susceptibility shows also a similar behavior in the parent phase of the three alloys, while in the intermediate phase, this behavior differs in the nontransforming alloy. In the latter case, the susceptibility shows an anomalous increasing during cooling down to 4.2 K. The continuous increase of the resonance frequency measured by resonant ultrasound spectroscopy and the anomalous increase of the magnetic susceptibility during cooling must be an intrinsic characteristic of the intermediate phase with no obvious relationship to the appearance of the martensitic transformation.The magnetic and vibrational behavior near a structural transformation in solids has been widely reported in the literature. In particular, it is well known that Ni 2 MnGa Heusler alloys and its off-stoichiometric analogs undergo a displacive martensitic transformation ͑MT͒ from a cubic L2 1 -ordered phase ͑Fm3m space group͒ to a low symmetry martensitic phase. The characteristics of the MT and the martensitic phases depend on the alloy composition. In the Ni-Mn-Ga alloys with e / a Ͻ 7.6, where e / a is the electron per atom concentration, MT is preceded by a weak first order transformation from the parent cubic phase ͑P phase͒ into a near-cubic intermediate phase ͑I phase͒ with a six-layered lattice modulation. 1,2 Several precursor phenomena occur prior to the P-I transformation during cooling; among them are the temperature dependent dip at a wave vector q Ϸ 0.33 inside the Brillouin zone ͑intracell distortion͒ and the softening of the long-wavelength limit of the acoustic TA 2 -phonon branch at q =0 ͑softening of the shear modulus CЈ͒. 1-12 The premartensitic transformation was shown experimentally and theoretically to be a result of the electronphonon coupling and Fermi-surface nesting enforced by a strong magnetoelastic interaction, 13-15 although any magnetic contribution is still disputed. 16 A comparative study of the temperature dependences of both the vibrational and magnetic characteristics of the Ni-Mn-Ga alloys which exhibit at a P-I soft-mode condensation in the high symmetry phase, while being either stable or unstable toward MT, can be helpful in understanding the nature of the intermediate soft-mode-condensed phase and accompanying phenomena. This Brief Report undertakes the characterizati...