Modulated phases occur in numerous functional materials like giant ferroelectrics and magnetic shape memory alloys. To understand the origin of these phases, we review and generalize the concept of adaptive martensite. As a starting point, we investigate the coexistence of austenite, adaptive 14M phase and tetragonal martensite in Ni-Mn-Ga magnetic shape memory alloy epitaxial films. The modulated martensite can be constructed from nanotwinned variants of a tetragonal martensite phase. By combining the concept of adaptive martensite with branching of twin variants, we can explain key features of modulated phases from a microscopic view. This includes phase stability, the sequence of 6M-10M-NM intermartensitic transitions, and magnetocrystalline anisotropy.DOI:

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Thin hydrogel films based on an ABA triblock copolymer gelator [where A is pH-sensitive poly(2-(diisopropylamino)ethyl methacrylate) (PDPA) and B is biocompatible poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC)] were used as a stimulus-responsive substrate that allows fine adjustment of the mechanical environment experienced by mouse myoblast cells. The hydrogel film elasticity could be reversibly modulated by a factor of 40 via careful pH adjustment without adversely affecting cell viability. Myoblast cells exhibited pronounced stress fiber formation and flattening on increasing the hydrogel elasticity. As a new tool to evaluate the strength of cell adhesion, we combined a picosecond laser with an inverted microscope and utilized the strong shock wave created by the laser pulse to determine the critical pressure required for cell detachment. Furthermore, we demonstrate that an abrupt jump in the hydrogel elasticity can be utilized to monitor how cells adapt their morphology to changes in their mechanical environment.

Magnetic field fluctuations arising from fundamental spins are ubiquitous in nanoscale biology, and are a rich source of information about the processes that generate them. However, the ability to detect the few spins involved without averaging over large ensembles has remained elusive. Here, we demonstrate the detection of gadolinium spin labels in an artificial cell membrane under ambient conditions using a single-spin nanodiamond sensor. Changes in the spin relaxation time of the sensor located in the lipid bilayer were optically detected and found to be sensitive to nearindividual (4 ± 2) proximal gadolinium atomic labels. The detection of such small numbers of spins in a model biological setting, with projected detection times of 1 s [corresponding to a sensitivity of ∼5 Gd spins per Hz 1/2 ], opens a pathway for in situ nanoscale detection of dynamical processes in biology.nitrogen-vacancy center | biophysics | nanomagnetometry T he development of sensitive and highly localized probes has driven advances in our understanding of the basic processes of life at increasingly smaller scales (1). In the last decade there has been a strong drive to expand the range of probes that can be used for studying biological systems (2-6), with emphasis on the detection of atoms and molecules in nanometer-sized volumes to gain access to information that may be hidden in ensemble averaging. However, at present there are no nanoprobes suitable for directly sensing the weak magnetic fields arising from small numbers of fundamental spins in nanoscale biology, occurring naturally (e.g., free radicals) or introduced (e.g., spin labels). These can be a rich source of information about processes at the atomic and molecular level. Magnetic resonance techniques such as electron spin resonance (ESR) have played an important role in the development of our understanding of membranes, proteins, and free radicals (7); however, ESR sensitivity and resolution are fundamentally limited to mesoscopic ensembles of at least 10 7 spins with a sensitivity of ∼2 × 10 9 spins per Hz 1/2 (8). In a typical ESR application, small electron spin label moieties are attached to the system of interest and their environment is investigated through spin measurements on the labels. Because of the large ensemble required, nanoscopic detail at the few-spin level can be lost in the averaging process. Recently, magnetic resonance force microscopy techniques have demonstrated single-spin detection (9-11), but these require cryogenic temperatures and vacuum. Here, we demonstrate a nanoparticle probe--a nitrogen-vacancy spin in a nanodiamond--which is situated in the target structure itself and acts as a nanoscopic magnetic field detector under ambient conditions with noncontact optical readout. We use this probe to detect near-individual spin labels in an artificial cell membrane at a projected sensitivity of ∼5 Gd spins per Hz 1/2 , effectively bridging the gap between traditional ESR ensemble-based techniques and the ultimate goal of few-spin nanoscale detection...

Diffusionless phase transitions are at the core of the multifunctionality of (magnetic) shape memory alloys, ferroelectrics and multiferroics. Giant strain effects under external fields are obtained in low symmetric modulated martensitic phases. We outline the origin of modulated phases, their connection with tetragonal martensite and consequences for their functional properties by analysing the martensitic microstructure of epitaxial Ni-Mn-Ga films from the atomic to macroscale.Geometrical constraints at an austenite-martensite phase boundary act down to the atomic scale. Hence a martensitic microstructure of nanotwinned tetragonal martensite can form. Coarsening of twin variants can reduce twin boundary energy, a process we could observe from the atomic to the millimetre scale. Coarsening is a fractal process, proceeding in discrete steps by doubling twin periodicity. The collective defect energy results in a substantial hysteresis, which allows retaining modulated martensite as a metastable phase at room temperature.In this metastable state elastic energy is released by the formation of a 'twins within twins' microstructure which can be observed from the nanometre to millimetre scale. This hierarchical twinning results in mesoscopic twin boundaries. Our analysis indicates that mesoscopic boundaries are broad and diffuse, in contrast to the common atomically sharp twin boundaries of tetragonal martensite. We suggest that observed extraordinarily high mobility of such mesoscopic twin boundaries originates from their diffuse nature which renders pinning by atomistic point defects ineffective.